Instantaneous measurement of M2 beam propagation ratio in real-time
Author(s):
Allen M. Cary;
Jeffrey L. Guttman;
Razvan Chirita;
Derrick W. Peterman
Show Abstract
A new instrument design allows the M2 beam propagation ratio to be measured in real time at the update
rate of a standard CCD camera. This allows lasers from single shot to CW to be measured while the laser
cavities are being adjusted. This drastically reduces the test time required for this operation. In this paper
we will discuss the theory behind this innovative approach to the M2 measurement and the methods for the
selection of the proper optical components for use of the system with various laser types and beam shapes.
The authors will show results of numerous measurements of different lasers and laser types, including solid
state diode and traditional gas lasers with M2 values from near 1 to considerably higher values, and show
comparisons these results with other measurement methods.
The instrument design is based on a method of simultaneous capture of the waist and several Rayleigh
ranges, allowing the instantaneous fit of the ISO M2 propagation curve. The authors will discuss the
important considerations necessary to generate accurate results for different laser configurations.
Q-switched lasing on a weak transition: new approach
Author(s):
Anatoliy Khizhnyak;
Vladimir Markov
Show Abstract
This paper discusses an novel strategy in development, design and integration of a high efficient Q-switched laser
operating on weak transitions of the lasing media. A typical example of such operation is lasing on the 946 nm transition
of Nd-doped medium. The proposed approach enables very effective Q-switched operation on this type of weak transitions with the plug-in efficiency better than 10% at a few ns pulse length, as compared to recently reported less than 1% efficiency at pulse length of about 150 ns.
Design and performance of a high-repetition-rate single-frequency Yb:YAG microlaser
Author(s):
Randal L. Schmitt;
Binh T. Do
Show Abstract
We describe the design and performance of a high-repetition-rate single-frequency passively Q-switched Yb:YAG
microlaser operating near 1030 nm. By using short cavity length, an intracavity Brewster polarizer, and an etalon output
coupler, we are able to produce ~1-ns-long single-frequency pulses at repetition rates up to 19 kHz without shot-to-shot
mode hopping. The laser's output spatial mode is TEM00 and its pulse energy varies between 31 μJ and 47 μJ depending
on repetition rate. Its peak optical-to-optical efficiency is 22%.
3-dimensional simulation of the solid state lasers
Author(s):
Christoph Pflaum;
Matthias Wohlmuth
Show Abstract
The optimization of output power and beam quality of a diode pumped solid state laser is a difficult task. In
this paper, we present a method to calculate approximate values of the beam quality factor M2 and the output
power of a laser. Our method is based on the well-known Gauss mode analysis combined with rate equations.
As an application we analyze the beam quality of a Q-switched solid state laser.
Injection seeded Nd:YAG ring laser generating 200 mJ Q-switched pulses
Author(s):
Anatoliy Khizhnyak;
Vladimir Markov;
Frank Wu
Show Abstract
This paper discusses a novel approach in a seeded Q-switched laser capable in oscillating with no mutual adjustment
between cavity resonances and seed emission frequency. The oscillation pulse of such a laser is easy to time-synchronize
to external processes. Oscillation of an injection seeded Q-switched Nd:YAG laser module is demonstrated that can laser
the pulses from several nsec to about 20 nsec long with the energy level higher than 100 mJ from the slave oscillator and
in excess of 200 mJ after a single stage amplification.
Stabilization technique for injection seeding Nd:YAG lasers using microwave range mode beating
Author(s):
Wytze E. van der Veer
Show Abstract
The conventional technique for matching and stabilizing the cavity length of
seeded Q-switched Nd:YAG lasers is to minimize the pulse build-up time in a lock-in
scheme. A disadvantage of this technique is that in order to obtain a robust feedback
signal the opening speed of the Q-switch needs to be reduced, which causes timing
issues, loss of power, and lengthening the generated pulse. Here an alternative method is
presented which mediates these problems. A feedback signal is obtained using
microwave frequency range detection of the beating between the longitudinal cavity
modes. This novel technique can be implemented with only a minimal modification of
the cavity optics and electronics of conventional free-running Nd:YAG lasers.
Very high-efficiency frequency-tripled Nd:YAG MOPA for spaceborne lidar
Author(s):
J. Luttmann;
K. Nicklaus;
V. Morasch;
S. Fu;
M. Höfer;
M. Traub;
H.-D. Hoffmann;
R. Treichel;
C. Wührer;
P. Zeller
Show Abstract
For spaceborne lidar like the atmospheric backscatter lidar (e.g. ATLID on the ESA EarthCARE mission) highly reliable and efficient laser sources are needed. As pre-development model we realized a Nd:YAG MOPA diode pumped at 100 Hz. With more than 21 % optical-optical efficiency the amplifier based on the InnoSlab design raises the 8 mJ pulse energy from the single frequency rod oscillator to more than 70 mJ. Frequency-tripling leads to more than 25 mJ at 355 nm and a beam quality of M2 < 1.7. The total optical-optical efficiency of more than 7.5 % exceeds the efficiency of comparable current lidar transmitter systems at least by a factor of 2. The laser is designed to cope with diode degradation or failure. Moderate pulse intensities in the InnoSlab amplifier offer excellent possibilities to scale the pulse energy to several 100 mJ in a most reliable and efficient way.
Recent progress on single frequency lasers for space and high altitude aircraft applications
Author(s):
F. E. Hovis;
J. Edelman;
T. Schum;
J. Rudd;
K. Andes
Show Abstract
The use of lidars in ground, airborne, and space-based missions can provide earth and planetary science measurements
that were previously unavailable. Our approach to the laser transmitters needed for such systems focuses on
developing environmentally hardened prototypes whose designs can be validated in fielded ground and airborne
remote sensing systems before being used in space-based missions. We are applying this approach to the
development of the injection seeded single frequency lasers that will be needed for a number of the next generation of
airborne and space-based lidar systems. In this paper we describe our most current version of a single frequency
Nd:YAG laser that is designed for use in an unpressurized, high altitude aircraft. It is capable of providing two 20 W
1064 nm output beams at 200 Hz. Temperature controlled ovens that hold the nonlinear crystals needed for frequency
doubling and tripling are included in the output path of one of the beams.
Frequency stabilization of nanosecond deep-ultraviolet coherent light source with injection seeding
Author(s):
Takeshi Yamamoto;
Yasutomo Shiomi;
Hiroshi Kumagai;
Ataru Kobayashi
Show Abstract
We have developed the advanced technology for the frequency stabilization of a nanosecond deep-ultraviolet coherent
light source toward manipulating semiconductor atoms by injection locking with a single-frequency Ti:sapphire laser. In
order to stabilize injection seeding, we utilized the small change of the build-up time of the slave-laser pulse. The injection-locked laser can acquire significant performances of both narrow linewidth and high peak power. As a result, the fluctuation of the wavelength decreases from 2.1 GHz to 10 MHz due to the injection seeding. The laser performance indicates various potentials useful for manipulating semiconductor atoms.
Laser technology developments in support of ESA's earth observation missions
Author(s):
Y. Durand;
J.-L. Bézy;
R. Meynart
Show Abstract
Within the context of ESA's Living Planet Programme, the European Space Agency has selected three missions
embarking lidar instruments: ADM-Aeolus (Atmospheric Dynamics Mission) planed for launch in 2009 with a Doppler
Wind Lidar, ALADIN, as unique payload; EarthCARE (Earth Clouds, Aerosols, and Radiation Explorer) planed for
launch in 2013 including an ATmospheric backscatter LIDar (ATLID); at last, A-SCOPE (Advanced Space Carbon and
Climate Observation of Planet Earth), candidate for the 7th Earth Explorer, relying on a CO2 Total Column Differential
Absorption Lidar.
To mitigate the technical risks for selected missions associated with the different sorts of lidar, ESA has undertaken
critical technology developments, from the transmitter to the receiver and covering both components and sub-systems
development and characterization.
The purpose of this paper is to present the latest results obtained in the area of laser technology that are currently ongoing
in support to EarthCARE, A-SCOPE and ADM-Aeolus.
Advanced pulsed thin disk laser sources
Author(s):
Christian Stolzenburg;
Andreas Voss;
Thomas Graf;
Mikhail Larionov;
Adolf Giesen
Show Abstract
Advanced pulsed thin disk laser sources based on several pulse generation schemes, including regenerative amplification
as well as cavity-dumping, will be presented. These sources are able to produce pulse energies in the multi-millijoule
range at repetition rates of up to several 100 kHz, resulting in average output powers in excess of 100 W. Also the
efficient intra-cavity frequency conversion of these sources will be discussed.
Industrial application of high power disk lasers
Author(s):
Rüdiger Brockmann;
David Havrilla
Show Abstract
Laser welding has become one of the fastest growing areas for industrial laser applications. The increasing cost
effectiveness of the laser process is enabled by the development of new highly efficient laser sources, such as the Disk
laser, coupled with decreasing cost per Watt. TRUMPF introduced the Disk laser several years ago, and today it has
become the most reliable laser tool on the market. The excellent beam quality and output powers of up to 10 kW enable
its application in the automotive industry as well as in the range of thick plate welding, such as heavy construction and
ship building.
This serves as an overview of the most recent developments on the TRUMPF Disk laser and its industrial applications
like cutting, welding, remote welding and hybrid welding, too. The future prospects regarding increased power and
even further improved productivity and economics are presented.
Scaling of thin disk pulse amplifiers
Author(s):
Jochen Speiser;
Adolf Giesen
Show Abstract
In the past decade, the Thin Disk laser design was very successful as a high power laser design for cw lasers with good
beam quality and high efficiency. Several numerical models show that the actually demonstrated output powers are far
below the scaling limits due to amplified spontaneous emission (ASE). Also pulsed lasers based on Thin Disk amplifiers
achieved comparable high average power, but only with medium pulse energies (about 100 mJ). Numerical models show
that ASE effects limit the possible pulse energy to values of a few Joule, using the typical high power cw Thin Disk laser
design.
To evaluate designs for higher pulse energies a time resolved numerical model of pump absorption and ASE was
developed and combined with a model of pulse amplification. The evaluation is focused on quasi-cw pumped pulse
amplifiers. It includes the analysis of temperature, stress, deformation and thermal lensing, using finite element methods.
This numerical model is used to develop thin disk designs for high output energies.
Erbium-based gas-cooled disk laser
Author(s):
John Vetrovec
Show Abstract
We report on a novel resonantly-pumped, erbium (Er)-based, gas-cooled disk laser (GCDL) scalable to highaverage
power (HAP). The GCDL uses edge-pumped composite laser disks known for their near perfect
pump uniformity and compact configuration. Edge pumping enables a long path for pump absorption, which
permits using low Er concentration and limits upconversion losses. Resonant operation reduces the waste
heat load and enables the use of gas rather than liquid for disk cooling. These attributes make it possible to
engineer a lightweight and compact laser device operating at eye-safer wavelengths. This paper presents a
GCDL concept design and evaluates its performance for several host materials and operating conditions.
Current status and development trends of disk laser technology
Author(s):
Alexander Killi;
Ivo Zawischa;
Dirk Sutter;
Jochen Kleinbauer;
Sven Schad;
Jörg Neuhaus;
Christian Schmitz
Show Abstract
This paper highlights unique advantages of the disk laser technology for converting the moderate brilliance of laser
diodes into excellent solid state laser beam quality with high efficiency. In contrast to traditional diode pumped
solid state lasers, particularly all relevant fluencies remain constant when the power is scaled by increasing the
active area of the disk. The state of the art TRUMPF disk laser family is presented, including latest results.
Theoretical and practical limits are discussed and an outlook over new disk laser generations including high
power cw, q-switched, and amplified systems is given.
Mode dynamics and thermal lens effects of thin-disk lasers
Author(s):
J. Mende;
J. Speiser;
G. Spindler;
W. L. Bohn;
A. Giesen
Show Abstract
In principle, the thin-disk laser concept opens the possibility to demonstrate high power, high efficiency and good beam
quality, simultaneously. For this purpose, a very homogeneous pump power distribution on the disk is necessary as well
as very low phase distortions of the disk itself.
Spatial mode structure and thermal lens effects in an Yb:YAG thin-disk laser have been investigated as function of the
pump power in linear and folded resonators. Whereas thermal lens is shown to be very weak due to the thin disk
geometry, a strong correlation of the laser mode with respect to the power density distribution of the pump radiation is
exhibited. The experimental results are compared with numerical simulations of the field distribution within the
resonator as well as in the far field demonstrating the excellent homogeneity of the disk as laser active medium.
Rotary disk lasers in the UV, the visible, and the infrared
Author(s):
Santanu Basu
Show Abstract
Rotary disk laser technology enables high-power nonlinear optics and laser machining. Due to the
wavelength dependence of laser-material interaction, the ability to scale laser power across the spectrum is
always in great demand in laser processing of materials. Rotary disk laser technology has enabled high-power
nonlinear optics by being able to produce in excess of 200 W in single-mode Q-switched laser power
at 1 micron. This breakthrough has led to the power scaling of single-mode visible lasers at 515 nm to 88 W
and single-mode UV lasers at 343 nm to 53 W which have set power performance record at their respective
wavelengths. In this paper, we will present the results of the rotary disk laser sources in the UV, the visible
and the infrared. We will also present record-breaking results in dicing and scribing of silicon, single crystal
sapphire and PCBs, and in hole drilling of stainless steel.
Concepts, features, and developments of slab laser oscillators and amplifiers
Author(s):
Keming Du
Show Abstract
Resulting from the optimal combination of slab shaped laser crystal, line shaped diode laser beam,
large area and one dimensional conduction cooling and hybrid-resonator design, slab lasers unify
features: high beam quality, short pulse duration, high pulse energy and high peak power, high
pulse repetition rate and average power and scalability at superior performances. In this paper,
concepts, features and developments of slab laser oscillators and amplifiers will be presented and
discussed.
Circular output from a high power Nd:YLF slab laser
Author(s):
J. I. Mackenzie;
W. A. Clarkson
Show Abstract
Neodymium-doped Yttrium Lithium Fluoride (YLF) lasers have traditionally been power-limited by the relatively
low tensile strength of the crystal. When power-scaling solid-state lasers, the choice of the gain media geometry, the
doping level, and the pumping scheme is dictated by minimizing the impact of thermally induced stress. To date the slab
architecture has been the most successful for scaling the average-power of Nd:YLF lasers due to its favorable thermal
management. However, for efficient high-radiance laser action it is also necessary to have a good overlap between the
cavity mode and the planar gain volume. We present the performance characteristics for an end-pumped slab-laser
utilizing a stable low-loss resonator configuration that transforms a circular cavity mode at the output coupler into a very
high aspect ratio elliptical beam in the slab gain element to match the pumped volume. The optical arrangement for
transforming the beam shape is also suitable for a double-pass slab amplifier configuration.
A polarized CW output power of 50W, on the weaker Nd:YLF 1053nm transition was obtained with a single slab
gain element and 110W of incident pump power from three spatially multiplexed diode bars. Laser threshold was around
7W and the slope efficiency, with respect to incident power, 46%.
Development of edge pumped Yb:YAG planar waveguide lasers
Author(s):
H. J. Baker;
J. F. Monjardin;
I. Thomson;
N. Trela;
J. D. R. Valera;
D. R. Hall
Show Abstract
A waveguide with 150 μm core height of 2% Yb:YAG between sapphire claddings is core-pumped at 480W by diode
bars coupled into the 13 mm long edge-facet. The pump unit has custom correction of collimation errors and lens
aberrations. Using a 6mm width and 7° edge-facet angle, power is limited by competing ASE loss or parasitic oscillation
along TIR-trapped internal paths, giving 40 W output for stable and 25 W for unstable resonators. Ray-tracing shows a
20° facet angle is necessary to successfully out-couple ASE from the core. Preliminary operation at 90W and an
increased threshold for the parasitic oscillation are obtained.
High-power slab-based Tm:YLF laser for in-band pumping of Ho:YAG
Author(s):
S. So;
J. I. Mackenzie;
D. P. Shepherd;
W. A. Clarkson
Show Abstract
Several remote sensing applications require pulsed sources in the mid-infrared spectral regime with high average
powers and good beam quality. Ho:YAG lasers have a number of attractive features for high power generation at
2.1microns, either for direct applications or as a pump source for parametric conversion to longer infra-red wavelengths.
Unfortunately, direct diode pumping of Ho:YAG is not practical, so a two-step process is generally employed in which
one or more diode-pumped thulium-doped lasers are used to directly pump (in-band) the Ho:YAG laser. In response, we
have investigated a slab-based architecture for scaling the output power of a Tm:YLF laser to the 100W power regime at
1.91microns, corresponding to a strong Ho:YAG absorption line. Multiple slab lasers with moderate beam quality in the
plane of the slab can be combined to efficiently end-pump a low-doping concentration Ho:YAG rod in a pump-guided
configuration. In a preliminary demonstration, two 2at.% doped Tm:YLF slab lasers with a spatially multiplexed output
of 74W were employed to end-pump a 1.5mm diameter, 80mm long, 0.25at.% Ho:YAG barrel-polished rod. A two-mirror
plano-concave cavity, with 11% output coupling transmission, produced a CW output of 38W with a slope
efficiency of 60% with respect to the incident power. Q-switched operation at a repetition rate of 20Hz with two intra-cavity
Brewster plate polarizers and a 60% transmitting output coupler produced 14mJ pulses with a pulse duration
(FWHM) of 18ns. This architecture offers an attractive route for future high-power 2micron lasers.
Pulsed passively mode locked operation of diode pumped Nd:GdVO4 and Nd:YVO4 in a bounce geometry
Author(s):
Václav Kubeček;
Michal Drahokoupil;
Helena Jelínková;
Andreas Stintz;
Jean-Claude Diels
Show Abstract
The operation of pulsed diode pumped Nd:GdVO4 and Nd:YVO4 slab lasers in a bounce geometry in a free running
and a passively mode-locked regime using a semiconductor saturable absorber was demonstrated. Higher efficiency of
Nd:GdVO4 in both regimes was achieved. In the free running regime the optical to optical efficiency of 28.3% was
obtained with Nd:YVO4 and 39.3% with Nd:GdVO4 crystal in spatial mode close to TEM00. In the passively mode
locked regime the Q-switched and mode locked single trains containing 5 pulses were generated for a pump energy of 11
mJ from Nd:YVO4 while the pump energy for Nd:GdVO4 was only 5.5 mJ. The pulse duration was 48 ps and 65 ps
respectively. Our results clearly demonstrate the advantage of using Nd:GdVO4 in a pulsed free running and also a
passively mode locked diode pumped regime in a bounce geometry.
Power scaling of fiber-based amplifiers seeded with microchip lasers
Author(s):
Paul E. Schrader;
Jean-Philippe Fève;
Roger L. Farrow;
Dahv A. V. Kliner;
Randal L. Schmitt;
Binh T. Do
Show Abstract
We summarize the performance of mode-filtered, Yb-doped fiber amplifiers seeded by microchip lasers with
nanosecond-duration pulses. These systems offer the advantages of compactness, efficiency, high peak power,
diffraction-limited beam quality, and widely variable pulse energy and repetition rate. We review the fundamental limits
on pulsed fiber amplifiers imposed by nonlinear processes, with a focus on the specific regime of nanosecond pulses.
Different design options for the fiber and the seed laser are discussed, including the effects of pulse duration,
wavelength, and linewidth. We show an example of a microchip-seeded, single-stage, single-pass fiber amplifier that
produced pulses with 1.1 MW peak power, 0.76 mJ pulse energy, smooth temporal and spectral profiles, diffractionlimited
beam quality, and linear polarization.
Hybrid fiber MOPA-bulk amplifier system for frequency conversion
Author(s):
Andrei N. Starodoumov;
Dave Dudley;
Stuart McLean;
Alexander Steinmetz;
Norman Hodgson
Show Abstract
We report on a hybrid fiber MOPA + solid-state amplifier for frequency conversion and compare a hybrid
scheme versus all- fiber MOPA. Using a thoroughly designed master oscillator and optimized fiber amplifiers we were
able to achieve 15-30ns long pulses at average powers above 20 W with a good spectral quality and suppressed SBS.
Bulk Vanadate amplifiers boosted the 1064nm output power to greater 65W at pulse repetition rates of 300-500 kHz.
More than 35 W in green and 20 W of UV light has been obtained at pulse repetition rates above 300 kHz and pulse
energies of 30-100 μJ.
Impact of energy-transfer-upconversion on the performance of hybrid Er:YAG lasers
Author(s):
Ji Won Kim;
J. K. Sahu;
W. A. Clarkson
Show Abstract
Using a hybrid fiber-bulk laser scheme based on Er:YAG, we have achieved ~60 W and ~30 W of continuous-wave
output at 1645nm and 1617nm respectively, and Q-switched pulse energies up to ~30 mJ (limited by coating damage).
Investigation of various factors influencing laser performance has revealed that energy-transfer-upconversion can have a
very detrimental impact on efficiency, even in continuous-wave mode of operation. In this paper we report on the results
of this study, discuss various measures for reducing energy-transfer-upconversion and its effect on laser performance,
and consider the prospects for further increase in output power and pulse energy.
High-power laser with Nd:YAG single-crystal fiber grown by micro-pulling down technique
Author(s):
Damien Sangla;
Nicolas Aubry;
Julien Didierjean;
Didier Perrodin;
François Balembois;
Kheirredine Lebbou;
Alain Brenier;
Patrick Georges;
Jean Marie Fourmigue;
Olivier Tillement
Show Abstract
We designed single-crystal fibers to combine excellent spectroscopic and thermo-mechanical properties of bulk crystals
and ability of pump guiding and good heat repartition of doped glass fibers. Such single-crystal fibers of excellent optical
quality were grown by the micro-pulling-down technique. A remarkable advantage of this technique is that pump
guiding is achieved in the directly grown fiber without additional polishing on the cylinder. We designed 0.2%-Nd doped
YAG crystal fibers sample of 50 mm and 1 mm diameter and AR coated on both end faces. It was longitudinally pumped
by a fiber-coupled laser diode with a maximum output power of 120 W at 808 nm. Laser emission at 1064 nm was
achieved inside a two concave mirrors cavity. We obtained 20 W of laser emission with a M2 quality factor of 6, for an
incident pump power of 120 W and a slope efficiency of 18% without any thermal management problems. Besides, a
power of 16 W with linearly polarized laser emission has been obtained under the same pump power by introducing a
thin plate polarizer in the cavity. An acousto-optical modulator was inserted inside the cavity and 360 kW of peak power
with 12 ns pulses at 1 kHz repetition rate were achieved under 60 W of pump power. This work shows real
improvements of laser performances in directly grown single crystal fibers. A complete thermal study confirms a good
heat management and demonstrates scalability to high average power laser sources.
Hybrid bulk/fibre MOPA system based on Yb:KYW laser
Author(s):
Sergey Kobtsev;
Sergey Kukarin
Show Abstract
In the present work we present results of studies of hybrid sub-picosecond systems based on a solid-state
Yb:KYW laser and a side-pumped fibre ytterbium amplifier manufactured using GTWave technology, which makes it
possible to remove completely from the fibre amplification path any discrete optical elements. When the system was
pumped with 12 W of CW radiation at 980 nm 0.9-ps output pulses with energy 40 nJ were generated at the repetition
frequency of 100 MHz and the average radiation power 4 W. The centre wavelength of the system could be detuned
within 1035-1055 nm (pulsed mode) and 1030-1070 nm (CW mode). Details are given of the layout of the femtosecond
Yb:KYW laser developed with the use of saturable absorber mirror and chirped mirrors. For the first time gain coefficients
of fibre GTWave Yb amplifier were measured within the generation range of the Yb:KYW laser. The developed
system is a promising source of controlled super-continuum radiation, since the radiation pulse wavelength may be
tuned around the zero dispersion wavelength of standard holey fibres (1040 nm) designed for super-continuum generation
when pumped in this spectral range.
High-performance optically pumped GaSb-based semiconductor disk lasers for the 2.Xum wavelength range
Author(s):
M. Rattunde;
N. Schulz;
B. Rösener;
C. Manz;
K. Köhler;
J. Wagner;
J.-M. Hopkins;
D. Burns
Show Abstract
We report on recent advances in the performance of GaSb-based optically pumped semiconductor disk lasers
(OPSDLs), emitting in the 2.0 - 2.3 μm wavelength range. Both barrier pumped OPSDL (using 980 nm laser
diodes as pump source) and in-well pumped OPSDL (using 1.96 μm pump radiation) have been fabricated
and characterized. Using alternative SiC or diamond intracavity heatspreader, multiple-watt CW-output
powers have been achieved (e.g. >3W at 2.3 μm and >5W at 2.0 μm), with power efficiencies in the range of
18 % - 25 %. For an optimised resonator setup, the beam profile is close to the diffraction limit with M2
values around 1.2; and even for the highest power levels, M2 is in the range of 2-5.
VECSEL subcavity design and optimization for targeted wavelengths
Author(s):
Hongbo Li;
Jörg Hader;
Jerome V. Moloney;
Stephan W. Koch
Show Abstract
Optically pumped semiconductor (OPS) vertical-external-cavity surface-emitting lasers (VECSELs) offer the first truly high-brightness high power laser sources with serious power scaling potential to multiple kW levels and flexible spectral coverage from IR to mid-IR. Due to the fact that the semiconductor chip (or subcavity) of a VECSEL serves as both the gain medium and a cavity mirror, the design and optimization of the semiconductor subcavity is key to achieve high power operation and consequently high power extraction via pump area scaling. A fundamental microscopic quantum design approach, allowing for calculating the electro-optical properties of QWs such as the optical gain/absorption and carrier recombination rates, is combined with a coupled optical-thermal-carrier analysis scheme to design and optimize VECSEL chips for wavelengths in the IR. We will describe the design and optimization procedure and present simulation results on VECSEL chips at wavelengths of 980 nm, 1178 nm, and 2 μm.
Interfacial misfit dislocation array based growth of III-Sb active regions on GaAs/AlGaAs DBRs for high-power 2 um VECSELs
Author(s):
G. Balakrishnan;
T. J. Rotter;
A. Jallipalli;
L. R. Dawson;
D. L. Huffaker
Show Abstract
This presentation will overview the growth of an IMF based VECSEL structure operating at 2 μm with an InGaSb QW
active region (a0 = 6.09 Å) on GaAs/AlGaAs distributed bragg reflectors (DBR) (a0 = 5.65 Å). The use of the GaAs
substrate instead of GaSb results in a significant reduction in the surface defect density while allowing the use of a
mature GaAs/AlGaAs DBR technology. We shall provide photoluminescence results from 2 μm IMF based active
regions grown on GaAs substrates and compare the results with the same active regions grown on GaSb substrates. We
shall also provide extensive transmission electron microscopy, surface morphology and high-resolution x-ray diffraction
analysis of the material grown.
Single-frequency tunable VECSEL around the cesium D2 line
Author(s):
B. Cocquelin;
G. Lucas-Leclin;
P. Georges;
I. Sagnes;
A. Garnache
Show Abstract
This work reports on an optically-pumped vertical external-cavity surface-emitting laser (VECSEL) emitting around
852 nm for Cesium atomic clocks experiments. We describe the design and the characterization of a VECSEL
semiconductor structure suitable for these applications. The parameters of the structure have been optimized in order to
have a low threshold and a high gain structure emitting around 852 nm. We achieved an output power of 330 mW for
1.1 W of incident pump power. We are able to simulate the laser emission variations with the temperature of the
substrate, the pump radius on the semiconductor structure and the losses inside cavity. A compact and robust setup was
built to obtain a stable single-frequency emission. We obtained a 17-mW single frequency emission exhibiting broad and
fine tunability around the Cesium D2 line.
Quantum design of active semiconductor materials for targeted wavelengths: a predictive design tool for edge emitters and OPSLs
Author(s):
Jerome V. Moloney;
Joerg Hader;
Stephan W Koch
Show Abstract
Performance metrics of every class of semiconductor amplifier or laser system depend critically on semiconductor QW
optical properties such as photoluminescence (PL), gain and recombination losses (radiative and nonradiative). Current
practice in amplifier or laser design assumes phenomenological parameterized models for these critical optical properties
and has to rely on experimental measurement to extract model fit parameters. In this tutorial, I will present an overview
of a powerful and sophisticated first-principles quantum design approach that allows one to extract these critical optical
properties without relying on prior experimental measurement. It will be shown that an end device L-I characteristic can
be predicted with the only input being intrinsic background losses, extracted from cut-back experiments. We will show
that textbook and literature models of semiconductor amplifiers and lasers are seriously flawed.
Comparison of thermal management techniques for semiconductor disk lasers
Author(s):
S. Giet;
A. J. Kemp;
D. Burns;
S. Calvez;
M. D. Dawson;
S. Suomalainen;
A. Harkonen;
M. Guina;
O. Okhotnikov;
M. Pessa
Show Abstract
Semiconductor Disk Lasers (SDLs) are compact lasers suitable for watt to multi-watt direct generation in the 670-
2350nm waveband and frequency-doubled operation in the ultraviolet and visible regions. This is, however, critically
dependent on the thermal management strategy used as, in this type of laser, the pump is absorbed over micrometer
lengths and the gain and loss are temperature sensitive. In this paper, we compare the two heat dissipation techniques that
have been successfully deployed to-date: the "thin device" approach where the semiconductor active mirror is bonded
onto a heatsink and its substrate subsequently removed, and the "heatspreader" technique where a high thermal
conductivity platelet is directly bonded onto the active part of the unprocessed epilayer. We show that for SDLs emitting
at 1060nm with pump spots of ~80µm diameter, the heatspreader approach outperforms the thin-device alternative, with
the best results being obtained with a diamond heatspreader. Indeed, the thermal resistances are measured to be 4.9, 10.4
and 13.0 K/W for diamond-bonded, SiC-bonded and flip-chip devices respectively. It is also observed, as expected, that
the thermal management strategy indirectly affects the optimum output coupling and thus the overall performance of
these lasers.
Ultrashort pulse Ti:sapphire oscillators pumped by optically pumped semiconductor (OPS) pump lasers
Author(s):
Bojan Resan;
Estelle Coadou;
Scott Petersen;
Aurelie Thomas;
Peter Walther;
Rimas Viselga;
Jean-Marc Heritier;
Juan Chilla;
William Tulloch;
Alan Fry
Show Abstract
Ultrashort pulse (USP) Ti:Sapphire oscillators are constantly improving in cost, performance, and reliability. These
improvements have been driven in part by improvements in the CW lasers used to pump the Ti:Sapphire gain medium.
Recent development of optically-pumped semiconductor (OPS) lasers heralds a USP pump source that reduces cost and
complexity while maintaining a high standard of performance and reliability. OPS lasers offer significant advantages
with respect to traditional diode-pumped solid state (DPSS) lasers in regards to wavelength flexibility, broad pump
tolerance, efficient spectral and spatial brightness conversion and high power scaling. In this paper, we report the
performance of different types of ultrashort pulse Ti:Sapphire oscillators pumped by OPS lasers: broad bandwidth
(approximately 100 nm) negative dispersion mirror based, broad bandwidth (approximately 100 nm) prism based, and
narrower bandwidth (approximately 10 nm) tunable prism based oscillator. We analyze the impact of multimode spatial
mode operation of the OPS pump laser on the mode quality, bandwidth and intensity noise of the USP oscillator output.
We compare the performance of USP oscillators pumped by multiple transverse mode OPS lasers with traditional single
transverse mode Nd:YVO4 DPSS lasers. We demonstrate excellent regenerative amplifier seeding with the OPS
pumped Ti:Sapphire oscillator.
Green laser modules to fit laser projection out of your pocket
Author(s):
U. Steegmüller;
M. Kühnelt;
H. Unold;
T. Schwarz;
R. Schulz;
S. Illek;
I. Pietzonka;
H. Lindberg;
M. Schmitt;
U. Strauss
Show Abstract
Among enabling key components for mobile laser projection, the green laser plays an outstanding role: We present green
laser modules based on frequency doubled optically pumped semiconductor disk lasers. In these lasers with twofold
conversion, from 808nm over 1060nm to 530nm, active semiconductor components and second harmonic generation
have to be carefully optimized to realize good efficiency at moderate output powers. The concept was developed not
only to meet power and efficiency targets, but also to provide simple operation and control by pump diode current. The
latest concept targets green output powers of more than 50mW at wall plug efficiencies >7%, limiting total electrical
power consumption to less than 1W. Consequent use of micro optical components allows for a package volume of less
than 0.5cm3.
1 W 488 nm cw air-cooled optically pumped semiconductor laser
Author(s):
Vasily Ostroumov;
Christoph Simon;
Heiko Schwarze;
Ruediger von Elm;
Wolf Seelert;
Jukka Lindfors
Show Abstract
We present an air-cooled optically pumped semiconductor laser that provides a cw output power of 1W at 488
nm. This performance was achieved via intracavity frequency doubling at a laser diode pump power of 2.5
Watts. The increased efficiency was realized by optimizing the OPS chip design and improving the heat
extraction from the OPS chip. Efficient cooling of the OPS chip and a compact and mechanically stable folded
resonator provide maintenance-free long life laser operation with an M2 of less than 1.1 and a noise of less than
0.25% rms. The size of the laser head is the same as for the 20 mW commercially available version, namely
125 x 70 x 34 mm.
Highly strained InGaAs/GaAs vertical-external-cavity surface-emitting laser for the generation of coherent yellow-orange light
Author(s):
Li Fan;
Chris Hessenius;
Mahmoud Fallahi;
Jörg Hader;
Hongbo Li;
Jerome V. Moloney;
Wolfgang Stolz;
Stephan W. Koch
Show Abstract
Optically pumped semiconductor vertical-external-cavity surface-emitting laser (VECSEL) potentially provides an
innovative approach to low-cost frequency agile lasers engineered for specific applications in infrared and visible range.
In this paper, we report on the development and demonstration of a multi-Watt highly strained InGaAs/ GaAs vertical-external-
cavity surface-emitting laser (VECSEL), which can be tuned from 1147 nm to 1197 nm. Based on this tunable
InGaAs/GaAs VECSEL and intracavity frequency doubling, we develop multi-Watt frequency-doubled tunable
VECSEL in a wide yellow-orange band (579 ~595 nm). This compact high-power yellow-orange laser provides an
innovative approach to an affordable guidestar laser (~589.1 nm) solution, and has a lot of important applications in
biomedicine.
1-W red light generation by intracavity doubling in a 1240 nm GaInNAs semiconductor disk laser
Author(s):
Jussi Rautiainen;
Antti Härkönen;
Pietari Tuomisto;
Janne Konttinen;
Lasse Orsila;
Mircea Guina;
Oleg G. Okhotnikov
Show Abstract
Owing to their good beam quality and high output power, near-infrared semiconductor disk lasers provide an attractive
opportunity for visible light generation via frequency conversion. The typical cavity arrangement of a semiconductor
disk laser, consisting of a semiconductor multiple quantum well gain mirror and one or more external mirror, offers a
convenient configuration for intracavity frequency doubling. Recent progress in the disk laser development has led to
demonstrations of multi-watt green-blue-yellow sources. These achievements have been enabled by the possibility to
integrate high performance InGaAs/GaAs gain media and Al(Ga)As/GaAs Bragg reflectors operating in the 940-1160
nm wavelength range. In order to achieve ~620 nm red emission, a laser emitting near the fundamental wavelength of
1240 nm is needed. To achieve this spectral range we have developed GaInNAs/GaAs gain mirrors and we have
achieved 1 W of output power at 617 nm by frequency doubling in a BBO crystal. This is to our knowledge the highest
power reported to date for intracavity doubled disk laser based on dilute nitride gain material.
80 W ultrafast CPA-free disk laser
Author(s):
J. Kleinbauer;
D. Eckert;
S. Weiler;
D. H. Sutter
Show Abstract
We present a CPA-free picosecond laser that will pave the way to cost effective industrial micromachining by operating
not only at high pulse energy but also at significantly higher average output power than previously achieved in commercial
ultrafast systems. The laser is based on a regenerative amplifier using a state-of-the art thin-disk laser head, and
includes an external modulator for user-adjustable pulse energy. 80 W of average power are demonstrated at a repetition
rate of 200 kHz and a duration of about 7 ps.
High average power Nd:YVO based pico-second regenerative amplifier
Author(s):
David A. Clubley;
Angus S. Bell;
Graham Friel
Show Abstract
We report on the development of a Nd:YVO4 based regenerative amplifier, producing more than 25W of average power
at 200kHz, with a pulse length of 10ps at 1064nm. The amplifier is seeded by a low power, mode-locked fiber laser. The
amplifier output has been used for the generation of high energy second and third harmonics with up to 80% conversion
to 532nm and 40% to 355nm. The average power of the amplifier has been increased further using a single pass linear
amplifier to produce 54W at 200kHz.
Design of transverse Nd doping profiles in transparent YAG ceramics for edge-pumped laser geometries
Author(s):
Jeffrey A. Wisdom;
Romain Gaume;
Roger Route;
Yan Lin Aung;
Akio Ikesue;
Robert L. Byer
Show Abstract
Edge-pumping Nd:YAG laser gain media is a convenient method to couple pump power into a laser cavity. A difficulty with this geometry is that for uniformly doped materials, pump power deposited near the edge of the gain medium cannot be efficiently extracted by a diffraction-limited beam. However, ceramic Nd:YAG with smooth changes in neodymium doping level (doping profiles) can now be fabricated to ameliorate this problem. A slab engineered with a doping profile that has a higher concentration of Nd in the center, and less at the edges, would allow more pump power to be efficiently extracted by a diffraction-limited laser beam. Yet this solution poses its own problem because variations in Nd concentration introduce optical path length distortions that can significantly reduce beam quality. The variations in optical path length are predominantly from changes in the refractive index of the host due to Nd doping and spatially varying temperatures. A genetic-algorithm-based approach is presented that balances improvement in mode-overlap between excited state distribution and the signal laser beam against optical path length distortions. A doping profile was found for an edge-pumped, zig-zag slab amplifier that is expected to yield a 39% improvement in extracted power delivered into a diffraction-limited spot compared to a uniformly doped slab.
1 W of 261 nm cw generation in a Pr3+:LiYF4 laser pumped by an optically pumped semiconductor laser at 479 nm
Author(s):
Vasiliy Ostroumov;
Wolf Seelert
Show Abstract
The lack of blue pump sources for Pr-doped materials has been overcome with the recent progress in optically
pumped semiconductor lasers (OPS) operating at 479 nm. The availability of reliable high power OPS pump lasers,
makes Pr3+-doped crystals ideal gain media for compact and efficient ultraviolet solid-state lasers with output power
in the Watt range.
We report on the scalability of a 522/261 nm Pr:YLF cw laser that is dual-end-pumped by two OPS lasers at 479 nm.
At 9.6 W of incident pump power more than 4 W were obtained at 522 nm with a slope efficiency of 45%.
Intracavity frequency doubling of 522 nm resulted in 1 Watt of cw UV output at 261 nm.
Fiber amplified and frequency doubled diode lasers as a highly flexible pulse source at 532nm
Author(s):
Kristian Lauritsen;
Sina Riecke;
Martin Langkopf;
Dietmar Klemme;
Christopher M. Kaleva;
Christopher Pallassis;
Shirley McNeil;
Rainer Erdmann
Show Abstract
Diode lasers provide a high degree of flexibility in signal shaping. Picosecond pulses with repetition rates from single shot to 80 MHz or arbitrary modulation formats with GHz bandwidth can be achieved through appropriate electrical drivers without changing the optical configuration. The limitations, however, of single mode diode lasers are low (mW) power levels and a lack of emission wavelengths between 470 and 630 nm. Optical amplification can extend single mode diode lasers to higher power levels where frequency doubling becomes a suitable option e.g. for producing green light at 530 nm. Ytterbium-doped fiber amplifiers (YDFA) show robust and stable operation at 1064 nm with amplifications of about 20 dB. We present a fiber amplified and frequency doubled diode laser that emits green picosecond pulses at variable repetition frequencies with an average output power of several milliwatts. Compared to existing semiconductor-amplified systems, higher stability at significantly smaller size and lower power consumption is achieved.
Continuous wave single longitudinal mode SHG with two stages of intra-cavity power enhancement at fundamental frequency
Author(s):
Fedor Karpushko
Show Abstract
In common intra-cavity SHG schemes, the requirement for high(st) level of fundamental frequency power inside the
non-linear crystal contradicts with the condition for extracting the maximum power available from the laser active
medium. This impedance mismatch problem is removed by using the fundamental frequency power enhancement in two
steps, the first one being optimized for maximum power outcoupling while at the second step the circulating inside
nonlinear crystal power is further increased for maximum efficiency of SHG process. Experimentally proved this
approach allows 3-5 times higher SH output power from DPSS lasers at given pump as compared with traditional
schemes.
High-power gain-enhanced internally frequency-converted Q-switched Nd:YAG lasers
Author(s):
Loren A. Eyres;
James J. Morehead;
Jeffrey Gregg;
Shannon Gomes
Show Abstract
Optimization of nonlinear coupling and use of aggressive Q-switch clipping on the pulse falling edge has enabled high
beam quality, internally frequency-converted, Nd:YAG lasers with output powers greater than 35 W at both green and
ultraviolet wavelengths. By retaining more energy in the rod after the pulse, such lasers operate with enhanced gain
levels and achieve greater nonlinear conversion. Operation in this gain-enhancement regime has enabled lasers with
highly variable pulse-widths. We demonstrate here that gain-enhanced laser operation with variable pulse energy and/or
delay between pulses is also possible. This combination of features and flexibility available in gain-enhanced,
frequency-converted lasers allows optimization of laser processing for a wide range of candidate materials.
Intracavity pumped Yb:SFAP crystal emitting at 985 nm and second harmonic generation
Author(s):
Marc Castaing;
François Balembois;
Patrick Georges;
Thierry Georges;
Kathleen Schaffers;
John Tassano
Show Abstract
We present what is, to the best of our knowledge, the first experiment of intracavity pumping at 914 nm of an
Yb:SFAP crystal emitting at 985 nm on the three-level laser transition. This configuration enabled us to indirectly
diode-pump this ytterbium doped crystal, and to obtain 1.4 W output power at 985 nm for 20 W of incident pump
power at 808 nm. Intracavity second harmonic generation has also been demonstrated in a KNbO3 crystal with a
total of 120 mW linearly polarized output power at 492.5 nm on two output beams.
Diode pumping of Nd:ASL and its frequency doubling for blue emission around 450 nm
Author(s):
David Paboeuf;
Gaëlle Lucas-Leclin;
Patrick Georges;
Bernd Sumpf;
Götz Erbert;
Cyrille Varona;
Pascal Loiseau;
Gérard Aka;
Bernard Ferrand
Show Abstract
We present the diode pumping of a Nd-doped strontium and lanthanum (Nd:ASL) crystal Sr1-xLax-yNdyMgxAl12-xO19 (0.05 ≤ x ≤ 0.5; y = 0.05) for second harmonic generation around 450 nm. In order to fulfill the pumping requirements of this
crystal, we have developed a high-brightness pump source based on a tapered amplifier in an extended cavity with a
volume Bragg grating for wavelength stabilization. A pump brightness of 110 MW.cm-2sr-1 has been obtained with a
linewidth lower than 80 pm at 798 nm. This laser source has been used to pump a Nd:ASL crystal to obtain 300 mW at
906 nm and 53 mW at 453 nm by intracavity doubling with a LBO crystal.
A diode-pumped Rb laser at 398 nm
Author(s):
A. B. Petersen;
R. J. Lane
Show Abstract
The CW diode-pumped alkali laser (DPAL) based on the rubidium resonance transition at 794.8 nm has been
investigated. The pump sources for these experiments are commercially available 780 nm fiber-coupled diode modules,
incorporating volume holographic gratings for wavelength control. Operating characteristics, pump architecture, power
scaling and lifetime limitations have been studied. To date, lasers pumped by single 20 W diode bars have produced
over 1 W output at 794.8 nm and 100 mW at the 397.4 nm harmonic. Lasers pumped by two 40 W diodes generate
almost 8 W at 794.8 nm.
Narrow linewidth ring laser with frequency doubling for titanium:sapphire and dye operation
Author(s):
Sven Hädrich;
Paulus Jauernik;
Lee McCrumb;
Philippe Feru
Show Abstract
We present a ring laser system that offers convenient exchange between titanium:sapphire and dye operation. Different
approaches reduce the short-term linewidth of the system, such as lock to the side of a fringe of a reference etalon and
using a Pound-Drever-Hall scheme, can be used for both configurations and are evaluated. Furthermore, titanium:sapphire and dye versions are compared regarding: efficiency, tuning range, linewidth, single-mode scan range, amplitude-noise and second harmonic generation.
Mid-infrared tunable laser based on the Cr:ZnSe active crystal
Author(s):
Petr Koranda;
Helena Jelínková;
Michal Nemec;
Jan Šulc;
Maxim E. Doroshenko;
Tasoltan T. Basiev;
Vitaly K. Komar;
Andriy S. Gerasimenko;
Vyacheslav M. Puzikov;
V. V. Badikov;
D. V. Badikov
Show Abstract
Broadly tunable mid-infrared laser sources operated at room-temperature are desired in many technological and
medical applications. The aim of the project was to design and construct broadly tunable powerful Cr:ZnSe laser.
The investigated Cr:ZnSe various shaped bulk crystals were grown by the Bridgman method or by the floating zone method. The absorption spectrum was measured to be from 1500 to 2000 nm and the emission spectrum was from 2100 to 2800 nm. Three different lasers were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser (generated wavelength 1660 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm) and diode-pumped Tm:YAP laser (generated wavelength 1980 nm). The constructed Cr:ZnSe laser operated in pulsed as well as in continuous-wave regime. In the first case the Cr:ZnSe crystal grown by the floating zone method was studied. The maximal output power in continuous-wave regime was 310 mW with the slope-efficiency 73% for the Tm:YAP laser pumping. In the second case the Cr:ZnSe prism grown by the Bridgman method which served simultaneously as laser active medium and intracavity dispersive element was investigated. For the Er:YAP laser pumping the maximal output energy was 20 mJ with the slope-efficiency 36%. The output radiation was tunable in the range from 2050 nm up to 2750 nm. For the Tm:YAP laser pumping the maximal output power in continuous-wave regime was 175 mW with the slope-efficiency 24%. The output radiation was tunable in the interval from 2220 nm up to 2680 nm. The generated radiation beam spatial structure was close to TEM00.
Tunable lasers based on diode pumped Tm-doped vanadates Tm:YVO4, Tm:GdVO4, and Tm:LuVO4
Author(s):
Jan Šulc;
Petr Koranda;
Pavel Černý;
Helena Jelínková;
Yoshiharu Urata;
Mikio Higuchi;
Witold Ryba-Romanowski;
Radosław Lisiecki;
Piotr Solarz;
Grażina Dominiak-Dzik;
Marcin Sobczyk
Show Abstract
Thulium doped vanadates Tm:YVO4 (5 at.% Tm/Y, grown by the Czochralski technique), Tm:GdVO4 (2 and
6 at.% Tm/Gd, grown by the floating-zone technique), and Tm:LuVO4 (3 at.% Tm/Y, grown by the floating-zone
technique) were investigated as an active medium for diode pumped tunable laser operating around 1.9 μm. For
thulium laser tuning single 1.5mm thick Brewster-angled birefringent quartz plate (Lyot filter) was placed in
simple 80mm long linear quasi-hemispherical resonator. For thulium doped vanadates pumping a fibre-coupled
(core diameter 400 μm) temperature-tuned laser diode operating in range from 799 up to 810nm was used
(max available power 20 W). All tested crystals were investigated under CW and pulsed pumping. Under pulsed
pumping (4% duty-cycle, reduced heat generation) lasing and laser tuning was demonstrated with all available
samples. Lasers were tunable in following wavelength ranges: Tm:YVO4 5 at.% Tm/Y (1841 - 1927 nm),
Tm:GdVO4 2 at.% Tm/Gd (1830 - 1982 nm), 6 at.% Tm/Gd (1850 - 2010 nm), and Tm:LuVO4 3 at.% Tm/Lu
(1860 - 1940 nm). Under CW pumping only Tm:GdVO4 crystal was lasing (lasing of Tm:YVO4 and Tm:LuVO4
was not reached under elevated pumping duty factor). Using Tm:GdVO4 (2 at.% Tm/Gd) the power up to 2.6W
and slope effciency ~ 30% (with respect to absorbed power at 808nm under lasing condition) was obtained at
wavelength 1.91 μm. Tunable operation with greater that 1W output and 130nm tuning range (1842 - 1972 nm)
was demonstrated for Tm:GdVO4 (2 at.% Tm/Gd) pumped at 802 nm.
High-power tunable external cavity quantum cascade laser in the 5-11 micron regime
Author(s):
Michael Pushkarsky;
Miles Weida;
Timothy Day;
David Arnone;
Russ Pritchett;
David Caffey;
Sam Crivello
Show Abstract
Daylight Solutions is currently developing field deployable, high power, wavelength agile, external cavity quantum
cascade lasers (EC-QCLs). These devices are finding uses as IR sources for applications such as remote gas sensing,
imaging, and illumination. Progress in three specific areas of development will be discussed: (i) miniaturization of a fast
tunable, moderate resolution, pulsed QCL for gas sensing, (ii) demonstration of high power mod hop free tunable CW
QCL's for high resolution spectroscopy, and (iii) progress in development of battery powered high efficiency fixed
wavelength EC-QCL light sources for molecular imaging and detection.
High-speed micromachining with high-power picosecond ultraviolet lasers
Author(s):
Ralf Knappe;
Achim Nebel
Show Abstract
Highest precision and minimal thermal impact is achieved, using picosecond laser pulses for micromachining. Virtually
any material can be processed with outstanding quality. The use of ultraviolet (UV) pulses can provide additional
benefits in higher throughput and improved edge quality for materials like metals, glasses, semiconductors or ceramics.
The advanced oscillator-amplifier (MOPA) laser design, based on reliable Nd:YVO4-systems, enables power scaling of
IR-pulses, and led to a series of laser systems with a repetition rate as high as 1 MHz and average power levels ranging
from 10 W to well above 50 W. Harmonic generation to the visible (532 nm) and the UV (355 nm) reaches efficiencies
of 50%, providing powerful beams for cost effective high-speed micromachining with high throughput.
Picosecond laser micromachining of advanced semiconductor logic devices
Author(s):
Jeffrey A. Albelo;
Peter Y. Pirogovsky;
James N. O'Brien;
Brian W. Baird
Show Abstract
Advanced semiconductor logic devices are increasingly complex, typically composed of multiple layers of dielectric,
metal, and semiconductor materials. Laser micromachining is employed on these devices to form cut-outs, microvias,
and perform partial material removal, including scribing and dicing operations. The recent development of high average
power (> 10 W), < 20 ps, 1064 nm diode-pumped mode-locked solid state lasers, operating at pulse repetition
frequencies > 100 KHz, enables an attractive short pulsewidth laser process alternative to existing nanosecond process
technologies, particularly for laser micromachining of complex alloy structures. Emerging 45 and 65 nm node logic
devices may contain greater than eight metal layers, typically aluminum and copper. They may also contain advanced low K layers which have proven difficult to process using conventional mechanical techniques, such as dicing saws. Efficient operation at 355 nm was readily achieved using extracavity conversion by employing non-critically phasematched LBO for SHG and critically phase-matched LBO for THG. Over 3 W at 355 nm at 100 KHz was achieved with an input of 8.5 W at 1064 nm. Preliminary micromachining results on advanced logic devices containing multiple low k and Cu layers at harmonic wavelengths (532 nm and 355 nm) yielded micromachining rates of > 300 mm/s with good workpiece quality.
High power UV q-switched and mode-locked laser comparisons for industrial processing applications
Author(s):
Michael Kauf;
Raj Patel;
Jim Bovatsek;
Wolfgang Gries
Show Abstract
It has been shown that micromachining of polymer materials using mode-locked, high repetition rate, 355nm picosecond
lasers is more efficient in respect to ablation rates and processing speeds, than using q-switched lasers at the same
wavelength and same average power level. In this study we present a systematic comparison of application results
obtained with q-switched nanosecond and mode-locked picosecond ultraviolet (UV) lasers. From the results, guidelines
are derived as to which laser type to use for best results depending upon material type and thickness. Additionally, recent
results obtained using a high power mode-locked UV picosecond laser - the PanteraTM - are described, along with
implications of how scaled-up power can significantly enhance processing efficiency in manufacturing environments.
Glass processing using q-switched ns INNOSLAB lasers
Author(s):
Keming Du;
Peng Shi
Show Abstract
In this talk we will present a novel glass processing technique using q-swicthed INNOSLAB lasers.
The mJ laser beam of some ns pulse length and beam quality of M2 < 1,3 from INNOSLAB laser is
focused into the glass to a very small spot. Because of the nonlinear absorption at high intensity
the laser energy is absorbed near the focus. This leads to micro cracks inside glass or localized
ablation, if the focus is on the glass surface. Using this mechanism glass can be proceeded at high
precision and speed.
Advanced Q-switched DPSS lasers for ID-card marking
Author(s):
Michael Hertwig;
Martin Paster;
Ralf Terbrueggen
Show Abstract
Increased homeland security concerns across the world have generated a strong demand for forgery-proof ID documents. Manufacturers currently employ a variety of high technology techniques to produce documents that are difficult to copy. However, production costs and lead times are still a concern when considering any possible manufacturing technology. Laser marking has already emerged as an important tool in the manufacturer's arsenal, and is currently being utilized to produce a variety of documents, such as plastic ID cards, drivers' licenses, health insurance cards and passports. The marks utilized can range from simple barcodes and text to high resolution, true grayscale images. The technical challenges posed by these marking tasks include delivering adequate mark legibility, minimizing substrate burning or charring, accurately reproducing grayscale data, and supporting the required process throughput. This article covers the advantages and basic requirements on laser marking of cards and reviews how laser output parameters affect marking quality, speed and overall process economics.
Nonlinear excitation fluorescence microscopy: source considerations for biological applications
Author(s):
David L. Wokosin
Show Abstract
Ultra-short-pulse solid-state laser sources have improved contrast within fluorescence imaging and also opened new
windows of investigation in biological imaging applications. Additionally, the pulsed illumination enables harmonic
scattering microscopy which yields intrinsic structure, symmetry and contrast from viable embryos, cells and tissues.
Numerous human diseases are being investigated by the combination of (more) intact dynamic tissue imaging of cellular
function with gene-targeted specificity and electrophysiology context. The major limitation to more widespread use of
multi-photon microscopy has been the complete system cost and added complexity above and beyond commercial
camera and confocal systems. The current status of all-solid-state ultrafast lasers as excitation sources will be reviewed
since these lasers offer tremendous potential for affordable, reliable, "turnkey" multiphoton imaging systems. This
effort highlights the single box laser systems currently commercially available, with defined suggestions for the ranges
for individual laser parameters as derived from a biological and fluorophore limited perspective. The standard two-photon
dose is defined by 800nm, 10mW, 200fs, and 80Mhz - at the sample plane for tissue culture cells, i.e. after the
full scanning microscope system. Selected application-derived excitation wavelengths are well represented by 700nm,
780nm, ~830nm, ~960nm, 1050nm, and 1250nm. Many of the one-box lasers have fixed or very limited excitation
wavelengths available, so the lasers will be lumped near 780nm, 800nm, 900nm, 1050nm, and 1250nm. The following
laser parameter ranges are discussed: average power from 200mW to 2W, pulse duration from 70fs to 700fs, pulse
repetition rate from 20MHz to 200MHz, with the laser output linearly polarized with an extinction ratio at least 100:1.
Solid state laser applications in photovoltaics manufacturing
Author(s):
Corey Dunsky;
Finlay Colville
Show Abstract
Photovoltaic energy conversion devices are on a rapidly accelerating growth path driven by increasing government and
societal pressure to use renewable energy as part of an overall strategy to address global warming attributed to
greenhouse gas emissions. Initially supported in several countries by generous tax subsidies, solar cell manufacturers
are relentlessly pushing the performance/cost ratio of these devices in a quest to reach true cost parity with grid
electricity. Clearly this eventual goal will result in further acceleration in the overall market growth. Silicon wafer
based solar cells are currently the mainstay of solar end-user installations with a cost up to three times grid electricity.
But next-generation technology in the form of thin-film devices promises streamlined, high-volume manufacturing and
greatly reduced silicon consumption, resulting in dramatically lower per unit fabrication costs. Notwithstanding the
modest conversion efficiency of thin-film devices compared to wafered silicon products (around 6-10% versus 15-20%), this cost reduction is driving existing and start-up solar manufacturers to switch to thin-film production. A key
aspect of these devices is patterning large panels to create a monolithic array of series-interconnected cells to form a low
current, high voltage module. This patterning is accomplished in three critical scribing processes called P1, P2, and P3.
Lasers are the technology of choice for these processes, delivering the desired combination of high throughput and
narrow, clean scribes. This paper examines these processes and discusses the optimization of industrial lasers to meet
their specific needs.
Tandem photonic amplifier employing a pulsed master oscillator fiber power amplifier with programmable temporal pulse shape capability
Author(s):
B. W. Baird;
X. Peng;
W. Ren;
D. M. Hemenway;
L. Xu;
P. Deladurantaye;
Y. Taillon
Show Abstract
We report on recent advances in the development of a 1064 nm pulsed master oscillator fiber power amplifier (MOFPA) with integrated modulators enabling programmable temporal pulse shapes and its employment in a tandem photonic amplifier. The MOFPA amplifier chain is seeded by a laser diode operated in the CW regime, yielding very stable spectral characteristics that are independent of the pulse repetition rate and pulse shape. The use of 3 GHz integrated LiNbO3 electro-optic modulators in conjunction with high speed digital electronics results in an excellent pulse shaping capability, a fine pulse amplitude stability and high repetition rate operation (100 kHz-1MHz) with fast rise times (<1ns). Energy per pulse of 8-10 μJ with good beam quality characteristics are obtained using advanced large mode area (LMA) fiber designs in the final power amplifier stage. The output is linearly polarized with a spectral bandwidth of < 0.1 nm. When employed in a tandem amplifier configuration, in which the MOFPA output is input to a single-stage, single-pass Nd:YVO4 amplifier pumped by a single 30 W fiber-coupled 808 nm diode, a 600 mW average power at 100 KHz signal input from the MOFPA was amplified to 6 W with faithful amplification of the input temporal pulse profile while achieving excellent beam quality (M2<1.1) and pulse amplitude stability (< ±3%, 3σ). A model of tandem amplifier performance shows good agreement with experimental results and indicates prospective performance of advanced tandem photonic amplifier configurations.
Optics performance at high-power levels
Author(s):
Ola Blomster;
Magnus Pålsson;
Sven-Olov Roos;
Mats Blomqvist;
Felix Abt;
Friedrich Dausinger;
Christoph Deininger;
Martin Huonker
Show Abstract
High laser power levels combined with increasing beam quality bring optics performance into focus. The subject of
optics performance is a hot topic, but lack of a common nomenclature, as well as of proper measurements, makes the
situation confusing. This paper will introduce a nomenclature for comparing the performance of different types of optics.
Further, the paper will present a test setup for characterizing optics, along with test results for different optics materials
and designs. The main influence of high power levels on optics is a focal shift along the optical axis. In industrial
applications, this might influence the performance of the process, especially if the focal shift is in the range of the
Rayleigh length. In the test setup that is to be presented, the optics are exposed to a high power beam, and a pilot beam is
used for measuring the change in focal position. For a proper description of optics performance, the laser beam
parameters should not influence the measured results. In the nomenclature that will be presented, the performance is
related to the Rayleigh length for a fundamental mode beam. The performance of optics when used with multimode
beams will be presented.
Advances in fiber delivery of ultrashort pulses at 800 nm
Author(s):
T. Le;
M. Hofer;
Z. Cheng;
A. Stingl;
J. Darmo;
D. P. Kelly;
K. Unterrainer
Show Abstract
Latest advances in femtosecond technology have strongly emphasized the control of ultra-short pulses in many
applications where the preservation of the pulse duration is most important. Recently, the delivery of ultra-short pulses
through optical fibers has become possible which opens up remarkable chances for simplifying optical setups or reaching
inaccessible regions. In this study we report on fiber delivery of 2 nJ and sub 65 fs pulses from a Ti:Sapphire laser
through 1.5 m LMA photonic crystal fiber. Application of such a fiber in an all-integrated THz imaging system to obtain
contactless information on the doping concentration of semiconductor wafers is shown.
Solid state saturable absorbers for Q-switching at 1 and 1.3 um: investigation and modeling
Author(s):
Jan Šulc D.D.S.;
Pavel Arátor;
Helena Jelínková;
Karel Nejezchleb;
Václav Škoda;
Milan R. Kokta
Show Abstract
Yttrium and Lutecium garnets (YAG and LuAG) doped by Chromium or Vanadium ions (Cr4+ or V3+) were
investigated as saturable absorbers potentially useful for passive Q-switching at wavelengths 1 μm and/or 1.3 μm.
For comparison also color center saturable absorber LiF:F-2 and Cobalt doped spinel (Co:MALO) were studied.
Firstly, low power absorption spectra were recorded for all samples. Next, absorbers transmission in dependence
on incident energy/power density was measured using the z-scan method. Crystals Cr:YAG, Cr:LuAG, V:YAG,
and LiF:F-2 were tested at wavelength 1064 nm. Therefore Alexandrite laser pumped Q-switched Nd:YAG laser
was used as a radiation source (pulse length 6.9 ns, energy up to 1.5 mJ). Crystals V:YAG, V:LuAG, and
Co:MALO were tested at wavelength 1338 nm. So diode pumped Nd:YAG/V:YAG microchip laser was used as a
radiation source (pulse length 6.2 ns, energy up to 0.1 mJ). Using measured data fitting, and by their comparison
with numerical model of a "thick" saturable absorber transmission for Q-switched Gaussian laser beam, following
parameters were estimated: saturable absorber initial transmission T0, saturation energy density ws, ground state
absorption cross-section σGSA, saturated absorber transmission Ts, excited state absorption cross-section σESA,
ratio γ = σGSA/σESA, and absorbing ions density. For V:YAG crystal, a polarization dependence of Ts was also
investigated. With the help of rate equation numerical solution, an impact of saturable absorber parameters on
generated Q-switched pulse properties was studied in plane wave approximation. Selected saturable absorbers
were also investigated as a Q-switch and results were compared with the model.
Big solar furnace as pumping source for high power lasers
Author(s):
Sh. Payziyev;
S. Bakhramov;
Sh. Klichev;
A. Kasimov;
T. Riskiev;
A. Abdurakhmanov;
A. Fazilov
Show Abstract
For effective conversion of the energy of the concentrated solar flux of 1 MW Big Solar Furnace of the Scientific and
Production Association "Physics-Sun" (Tashkent) with focal spot size of about 40 cm into the coherent laser radiation,
the several designs of the multi-element secondary concentrators for various active mediums with different thermal and
optical characteristics were considered. For calculations of parameters of secondary concentrators the Ray tracing and
Monte-Carlo methods were used and the numerical experiments were performed.
Power scaling and optimum crystal orientation in continuous-wave diode-pumped Yb:KLu (WO4)2 lasers
Author(s):
Junhai Liu;
Valentin Petrov;
Xavier Mateos;
Huaijin Zhang;
Jiyang Wang
Show Abstract
Monoclinic potassium double tungstates are biaxial laser materials characterized by strong anisotropy of the spectroscopic properties. KLu(WO4)2 is the most attractive of them in the case of Yb-doping because of the close ionic radii of Yb and Lu. In this work we compare crystals of equal dimensions and doping level but different cuts, under the same pumping conditions. Special emphasis is placed on the polarization behavior. We present substantial power scaling with KLu(WO4)2 in the continuous-wave regime by longitudinal fiber-coupled diode laser pumping. Slope efficiency of roughly 80% is achieved while the naturally selected laser polarization is parallel either to the Np or Nm principal optical axes. A maximum output power of 11.0 W was produced from a 2 mm thick uncoated crystal with Ng-cut, the corresponding optical-to-optical efficiency was 68%.
Ceramic Nd3+:Cr3+:YAG laser pumped by high-power concentrated solar flux
Author(s):
Sh. Payziyev;
S. Bakhramov;
H. Yagi;
A. Abdurakhmanov;
A. Fazilov
Show Abstract
Recently, fabrication of new laser materials with broadband absorption spectrum by ceramic technology allowed to
receive the effective generation of coherent lights at lamp pumping. Due to this has appeared the new perspective
opportunities for creation of high-efficient solar pumped lasers on the Nd3+:Cr3+:YAG ceramics.
In this paper the possibility of application of the Nd3+:Cr3+:YAG ceramics for pumping by concentrated solar flux of the
Big Solar Furnace with 1 MW power is considered.
Long-term frequency stabilisation of a CW single-frequency laser using a high-precision wavelength meter
Author(s):
Sergey Kobtsev;
Stepan Kandrushin;
Andrey Potekhin
Show Abstract
In the present paper it has been demonstrated that the suggested and for the first time experimentally tested method
for considerable reduction in long-term radiation frequency drift of CW single-frequency Ti:Sapphire and dye lasers
based on a fast high-precision radiation wavelength meter and a digital-analogue feed-back system can present an
efficient alternative to conventional methods for long-term frequency stabilisation. Long-term frequency drift of the
lasers was improved from ~450 MHz/h in free-running regime to less than 40 MHz/h in the regime of frequency stabilisation.
Application of a wavelength meter as a spectral reference allows reduction in the long-term frequency drift down
to the level of residual drift inherent in the wavelength meter. An interesting prospective feature of the suggested method
is the possibility to use a wavelength meter for periodical operative wavelength correction of more than one laser, which can also be performed remotely when a laser and the wavelength meter are connected with a long optical waveguide and the wavelength value is transmitted though the Internet. The proposed method of stabilisation can be used for single-frequency lasers of any type (solid-state, diode, fibre, dye lasers, etc.), in which continuous controlled radiation frequency detuning is possible.
Output characteristics of a passively Q-switched diode-laser pumped ceramic Nd:YAG laser
Author(s):
Duck-Lae Kim;
Beom-Seok Lee;
Hee-Sang Yoo;
Jae-Yong Jeong;
Yeong-Sik Kim
Show Abstract
A passively Q-switched diode-laser pumped ceramic Nd:YAG laser has been constructed and the output characteristics
has been investigated. The output efficiency of 36.1 % has been obtained with 1.1 at.% of neodymium concentration in
the ceramic YAG. For the case of neodymium concentration of 2.0 at.%, the output power decreases as the pump power
increases over 6 W. The output power has rapidly decreased more than 10 W of pumping, and the laser output has finally
disappeared at pumping power of 13 W. This phenomenon can be explained by the thermal lens effect in the laser
material. Passive Q-switching has been carried out using a Cr:YAG crystal in the resonator. The pulse width is 61.2 ns
and the repetition rate is 10.1 kHz at the pump power of 1 W. The beam propagation factor M2 has been measured to be
1.2, which shows good beam quality of the Q-switched pulse.
High-peak-power diode-pumped actively Q-switched Nd:YAG intracavity Raman laser with an undoped YVO4 crystal
Author(s):
K. W. Su;
Y. T. Chang;
Y. F. Chen
Show Abstract
The efficient stimulated Raman scattering conversion in a diode-pumped actively Q-switched Nd:YAG laser was
achieved with an undoped YVO4 crystal as a Raman shifter. With an incident pump power of 16.2 W, 1176-nm first
Stokes average output power of 2.97 W was generated at a pulse repetition rate of 50 kHz. The maximum pulse energy
is higher than 83 μJ at both 20 kHz and 30 kHz. With mode-locked modulation, the effective pulse width far above
threshold is usually below 5 ns. With an incident pump power of 7.62 W, the peak-power of 43.5 kW was demonstrated
at 20 kHz.
AlGaInAs quantum-well 1.3-μm laser by a diode-pumped actively Q-switched Nd:GdVO4 laser
Author(s):
S. C. Huang;
K. W. Su;
A. Li;
S. C. Liu;
Y. F. Chen;
K. F. Huang
Show Abstract
We report a high-peak-power AlGaInAs 1.36-μm vertical-external-cavity surface-emitting laser (VECSEL)
optically pumped by a diode-pumped actively Q-switched Nd:GdVO4 1.06-µm laser under room-temperature operation.
The gain medium is an AlGaInAs quantum wells (QWs)/barrier structure grown on a Fe-doped InP substrate by
metalorganic chemical-vapor deposition. With an average pump power of 1.9 W, an average output power of 340 mW
was obtained at a pulse repetition rate of 40 kHz, corresponding to an optical-to-optical conversion efficiency of 18.76%.
With a peak pump power of 7.9 kW, the highest peak output power was 1.3 kW at a pulse repetition rate of 10 kHz.
High-power Kerr-lens mode-locked ytterbium lasers
Author(s):
F. M. Bain;
A. A. Lagatsky;
C. T. A. Brown;
W. Sibbett
Show Abstract
Progress in the development of efficient and reliable diode-pumped ytterbium femtosecond laser systems based on Kerr-lens
mode locking effect is reported. Average output power of up to 1 W is demonstrated in a Kerr-lens mode locked
Yb:YVO4 laser with pulse durations as short as 80 fs at a pulse repetition frequency of 79 MHz. Measurements of the
nonlinear refractive indexes of the Yb3+:YVO4 crystal, n2, were performed and were determined to be 39×10-16 cm2/W
and 49×10-16 cm2/W for E||c and E⊥c polarizations, respectively. These results were found to be in a good agreement
with those calculated using both the Kramers-Krönig relation and Boling, Glass and Owyoung formula.
Keywords: Mode-locked lasers, diode-pumped lasers
1.
High-peak-power flashlamp-pumped passively Q-switched Nd:YAG laser with AlGaInAs quantum wells as a saturable absorber
Author(s):
H. C. Liang;
J. Y. Huang;
S. C. Huang;
K. W. Su;
Y. F. Chen;
K. F. Huang
Show Abstract
We demonstrate an AlGaInAs saturable absorber with a periodic quantum wells (QWs)/barrier structure that can be
used to achieve an efficient high-peak-power and high-pulse-energy passively flashlamp-pumped Q-switched Nd:YAG
laser at 1.06 um. The barrier layers are designed to locate the QW groups in the region of the nodes of the lasing standing
wave to avoid damage. With an incident pump voltage of 14.5 J, a single pulse was generated with a pulse energy of 14
mJ and a Q-switched pulse width of 13 ns. The maximum peak power was greater than 1.08 MW.
Diode pumped Tm:YAP laser for eye microsurgery
Author(s):
Helena Jelínková;
Petr Koranda;
Jan Šulc;
Michal Nemec;
Pavel Černý;
Jiří Pašta M.D.
Show Abstract
Pulsed tunable diode-pumped Tm:YAP laser was characterized and used for preliminary investigation in eye
microsurgery. By means of Lyot filter, the laser emission was tuned between a high (120 cm-1 @ 1940 nm) and two
times lower (50 cm-1 @ 2040 nm) value of radiation absorption in water.
In the interaction experiment, the eye tissue (in vitro) was irradiated with tunable Tm:YAP laser radiation, and the effects
of cutting and coagulation depth in wavelength range from 1940 nm up to 2040 nm were investigated. The results were
documented by optical microscope.
Ultrashort lasers: identifying the "perfect" pulse
Author(s):
Daniel A. Bender;
Mansoor Sheik-Bahae
Show Abstract
Sensitive, real-time chirp and spectral phase diagnostics along with full field reconstruction of femtosecond laser pulses
are performed using a single rapid-scan interferometric autocorrelator. Single shot diagnostics are possible when the
second-harmonic spectrum is available. A novel graphical representation distinguishes between temporal and spectral
phase distortions. Examples are presented that illustrate the sensitivity and fidelity of the scheme even with low signal-to-
noise.
Tunable pulsed forsterite laser operating at room temperature
Author(s):
Frank F. Wu
Show Abstract
Pumped by a Q-switched Nd:YAG laser operating at 1064 nm and its frequency-doubled 532 nm, a maximum energy of 2.5 mJ
and a tuning range of 1206-1315 nm were obtained experimentally for a forsterite laser at room temperature. A theoretical
analysis and calculation including the tunable and output characteristics of this chromium-doped forsterite laser is presented in
this paper.
A new compact laser source for portable LIBS applications
Author(s):
J. Goujon;
O. Musset;
A. Giakoumaki;
V. Pinon;
D. Anglos;
E. Georgiou
Show Abstract
We present LIBS experimental results that demonstrate the use of a newly compact, versatile pulsed laser source in
material analysis in view of research aiming at the development of portable LIBS instrumentation. LIBS qualitative
analyses were performed on various samples and objects, and spectra were recorded in gated and non-gated modes. The
latter is important because of advantages arising from size and cost reduction when using simple, compact spectrograph-CCD detection systems over the standard ICCD-based configurations. The new Nd3+:YAG laser source exhibited very
reliable performance in terms of laser pulse repeatability, autonomy and interface. Indeed, it can deliver a 45 mJ for 4.5 ns
pulse and work at 1 Hz. Having the ability to work in double-pulse mode, it provided versatility in the measurements
leading to increased LIBS signal intensities, improved the signal noise ratio and stabilized spectra. The first test results are
encouraging and demonstrate that this new laser is suitable for integration in compact, portable and low cost LIBS sensors
with a wide spectrum of materials analysis applications.
Room-temperature mid-infrared Cr2+:ZnSe and Cr2+:ZnS random powder lasers
Author(s):
C. Kim;
D. V. Martyshkin;
V. V. Fedorov;
S. B. Mirov
Show Abstract
We report a simple method for fabricating transition metal (TM) doped II-VI powders with average size of about 10-
20μm as well as room temperature mid-infrared (2-3 μm) random lasing based on Cr2+-doped ZnSe and ZnS powders
prepared without crystal growth stage under optical intra-shell excitation of chromium. Fabrication of Cr2+-doped ZnSe
and ZnS powders involved two simple stages. At the first stage, pure ZnSe, (ZnS) and CrSe, (CrS) (with a concentration
of Cr2+ ion 2×10-19 cm-3 and 5 × 10-19 cm-3 for ZnSe and ZnS respectively) chemicals with an average grain size of 10μm were uniformly mixed by means of a mechanical shaker. At the second stage the obtained ZnSe/CrSe mixture was sealed into evacuated (~10-4 Torr) quartz ampoule and annealed either at 1200°C for 15 minute, or 1000°C for 3 days. In
the case of ZnS/CrS mixtures the annealing was performed in evacuated quartz ampoule at 1000 °C for 14 days. After
annealing, under 1560 nm excitation, the powders demonstrated room temperature middle-infrared luminescence of Cr2+
similar to Cr2+ emission in bulk ZnSe and ZnS. Moreover, the output-input characteristic clearly demonstrated the
threshold-like behavior of the output signal with the threshold pump energy density of ~44.5 mJ/cm2 ~7.46 mJ/cm2, and 63.6 mJ/cm2 for Cr:ZnSe annealed for 15 min, 3 days, and Cr:ZnS respectively.
Q-switched laser operation of Yb-doped NaGd(WO4)2 and NaY(WO4)2 crystals
Author(s):
Junhai Liu;
Valentin Petrov;
Huaijin Zhang;
Jiyang Wang;
Minhua Jiang
Show Abstract
The tetragonal double tungstates NaGd(WO4)2 and NaY(WO4)2 are uniaxial crystals which can be grown from the melt
by the Czochralski method and exhibit disordered crystalline structure. The structural disorder leads to additional
inhomogeneous broadening of the spectral features of the doping rare-earth ions. We report on passive Q-switching of
Yb:NaGd(WO4)2 and Yb:NaY(WO4)2 lasers operating near 1 μm using a Cr4+:YAG saturable absorber in a simple,
diode end-pumped plano-concave resonator. With both crystals average powers of roughly 2 W were obtained for pulse
durations of ≈30 ns and single pulse energy of ≈150 μJ at kilohertz repetition rates (roughly from 1 kHz to above
10 kHz). The maximum slope efficiency achieved in the Q-switched mode of operation was 40%.
Iron doped CdxMn1-xTe crystals: new gain media for mid-IR room temperature lasers
Author(s):
W. Mallory;
V. V. Fedorov;
S. B. Mirov;
U. Hömmerich;
W. Palosz;
S. B. Trivedi
Show Abstract
The objective of this study is to determine feasibility of ternary Fe:CdMnTe crystals for room temperature lasing in the
mid-infrared spectral range. Fe:CdMnTe samples were grown with a modified Bridgman technique. At room temperature, Fe:CdMnTe features wide (2800-6000nm) absorption and emission (3700-6500nm) bands. The kinetics of the photoluminescence were measured over 14K-300K temperature range under 2920nm and 532nm excitation. The low temperature (14K) kinetic of luminescence under 2920nm excitation was a single exponential with a decay time of 75μs. The room temperature emission cross-section was estimated to be 2x10-18cm2.
Two-stage concentrating systems for pumping of solar lasers
Author(s):
Sh. Klichev;
S. Bakhramov;
A. Abdurakhmanov;
A. Fazilov;
Sh. Payziyev;
A. Ismanjanov;
K. Bokoev;
J. Dudko;
Z. Klichev
Show Abstract
One of the ways to increase the concentrating ability of solar concentrators used for pumping of lasers is an additional
concentration of a sunlight by a secondary concentrator allocated in a focal area of the primary concentrator. Limiting
concentrations of those compound systems on the basis of non-imaging optics have been received by Winston. However
more detailed calculations on the basis of irradiance integral are necessary for designing and practical realization of such
systems. It is especially important for the systems including generally compound of two secondary concentrators. The
full design procedure for concentration by systems of type compound parabolic concentrator or Winston concentrator
(focon) and a cone concentrator is developed in the work in view of real distribution of brightness on a solar disk and
discrepancies of primary concentrator geometry. The generalized dependences of efficiency of compound systems for
the maximal and mean concentration in a focal plane of the primary paraboloidal concentrator depending on its
disclosing angle U0 and discrepancies of geometry are received.
It is shown, that focon only up to U0 < 30° is more effective, than the cone and further their efficiencies are identical. It is
shown, that secondary concentrator allows to increase the pumping efficiency not less, than 30%.
Generalized phase synchronization in unidirectionally coupled LD pumped Nd:YAG lasers
Author(s):
Dae-Sic Lee;
Guang-Hoon Kim;
Seung Yup Lee;
Chil-Min Kim
Show Abstract
We experimentally investigate phase synchronization between two detuned response chaotic laser systems coupled to a
slightly different drive oscillator. Our result is that phase synchronization can occur between response laser systems
when they are electronically driven by correlated (but not identical) inputs from the drive oscillator. We call this
phenomenon generalized phase synchronization and clarify its characteristics using temporal behaviors and phase
portraits.