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LASE talks sampler

Because there is just too much going on to see it all: here is a small sampling of presentations heard at SPIE Photonics West 2016.

LASE symposium SPIE Photonics West


From the LASE Symposium


Amplifying metasurface mirrors for THz-Qc lasers

Luyao Xu of the University of California, Los Angeles, (9734-15) in a session Monday afternoon session on novel technologies in the conference on Vertical External Cavity Surface Emitting Lasers (VECSELs) provided interesting insights about breakthrough research on creating the first VECSEL that operates in the terahertz (THz) range.

The results were enabled by using a metasurface reflector array composed of subwavelength antenna-coupled quantum-cascade (QC) cavities, so that when a terahertz wave hits the array, it doesn't see the cavities but instead the mirror amplifies the incoming waves as well as reflecting them.

The system offers several advantages over the conventional THz-QC lasers such as improved beam pattern as well as the ability to continuously tune the output coupling efficiency with the polarization angle until optimized/desired output power is achieved. These new developments in this technology are paving the way towards making VECSEL a functionally versatile system for a plethora of applications in chemical sensing, semiconductor, space exploration, and defense.


Fiber lasers fast moving forward to 2μm

Tuesday morning's opening session on "2μm Laser Components: European ISLA Program session" in the conference on Components and Packaging for Laser Systems (9730) provided updates on major advances in a series of interdependent components accomplished by ISLA, a three-year project supported by the European Commission aiming to push forwards the boundaries of current laser material processing technology.

Gary Stevens, Gooch & Housego (Torquay) Ltd. (9730-1) presented results on the developments of various passive components like ultra-wideband fused fiber couplers and combiners as well as high power PM and non-PM fiber-in fiber-out optical isolators for 2 µm fiber lasers.

Jon Ward, Gooch & Housego PLC (9730-2) discussed the new types of acousto-optic modulators (AOMs) that facilitate extremely narrow resolution capabilities with little or no polarization dependence. Also presented were designs for acousto-optic tunable filters (AOTF) that gave a substantially net zero frequency-shift with very little or no loss of pointing stability in presence of small controlled frequency-shifts.

Kangpeng Wang and his team at Trinity College Dublin (9730-3) exploited the optoelectronic properties of graphene to develop graphene saturable absorber mirrors (SAMs) for application as passive mode-lockers and generate 2 µm ultrashort pulses. Results indicated that graphene SAMs can be fabricated with ease at much lower costs and offer performance comparable with the conventional commercial obtained SESAMs (semiconductor saturable absorber mirrors).

Andrew Clarkson from Univervisty of Southampton (9730-4) reported recent developments on pump laser diodes at 793 nm for optimized high-power applications such as thulium (Tm) doped double-clad fiber pumping. Results revealed that with optimized core composition and doping profile, efficiencies close to the theoretical limit of ~80% can be achieved.


Measuring nonlinear refraction in gases

Eric Van Stryland of CREOL at the University of Central Florida (9731-46) in a keynote talk Tuesday afternoon in the Nonlinear Frequency Generation and Conversion conference Tpresented a technique for measuring and predicting nonlinear responses of gases.

By analyzing the beam deflection of kHz lasers on quad-cell segmented photodiodes, an absolutely calibrated, high-sensitivity measurement of both nonlinear absorption and nonlinear refraction of gases can be achieved. Other techniques, such as optical Kerr effect experiments, are only capable of measuring induced birefringence, and not the nonlinear refractive index, n2.

Van Stryland primarily used the example of carbon disulfide gas, and showed results of the full temporal response function of the deflection as polarization was manipulated. The technique provides a dynamic characterization of materials, and is a natural complement to other experimental processes such as the Z-scan.


Minimizing laser plasma instabilities

"Yes, we blow things up," Matthias Geissel, Sandia National Labs, began his talk (9731-22) Wednesday morning in the conference on Nonlinear Frequency Generation and Conversion.

Sandia is home to the world's most powerful electric x-ray generating device, the Z machine, capable of producing up to 100 TW. The Z machine is used to study energy generation from magnetized linear inertial fusion (MagLIF). Firing the Z machine is a destructive process, meaning all experiments must be carefully designed.

In MagLIF, a discharge current across a gas chamber is used to produce a strong magnetic field. The ionized gas and magnetic field subsequently become "frozen together," so that compression of the gas affects the strength of the magnetic field. In this way, the densities and temperatures required for thermonuclear fusion can be achieved.

Geissel presented recent strategies in reducing laser plasma instabilities (LPIs) in the system, caused by momentum and energy transfer to both ions and electrons in the system (simulated Brillouin scattering and stimulated Raman scattering, respectively).

One such method is pre-heating the fusion targets to inhibit losses to cold walls. While there were improvements, the "puzzle is not yet solved." We "will always have LPI," Geissel concluded, it just a matter of minimization "to be able to live with it."


The rod-type photonic crystal fiber odyssey

Optical fibers have proved to be one of the breakthrough successes of modern-day technology, particularly in telecommunications for transmitting information as short optical pulses over long distances. Yet the basic physics of the conventional optical fibers has not changed much since the 19th century, with new developments only providing incremental improvements to individual components.

Since the technology's invention in 2003, photonic crystal fibers (PCFs) have taken a step forward in revolutionizing the ability of optical waveguides to provide high-power short pulses, by fundamentally changing the way light can be generated, delivered and used.

The Wednesday morning Pioneers session on early development of active PCFs chaired by Fabio Di Teodoro, Raytheon Co., detailed the basic physics behind PCF fabrication and highlighted how new rod-type PCFs could be developed at large-scales (9728 Session 13).

The speakers -- Jens Limpert, Friedrich-Schiller-Univ. Jena; François Salin, MoriaLase/ EOLITE Systems; and Thomas Tanggaard Alkeskjold, NKT Photonics A/S -- discussed the reliability, diffraction-limited beam quality, and high output power of PCFs that make them most ideal for realizing high-power femtosecond laser systems for the next generation.

Giving a snapshot of the current state of the art, the speakers discussed key research and commercialization facets that would govern the translation as well as sustainability of these sophisticated active PCFs in the highly competitive industrial market.


Improving surgery speed and precision with 3D printed templates

In its third year at SPIE Photonics West, the Laser and 3D Manufacturing conference strives to be an effective platform to facilitate crosstalk between disciplines and novel applications. One such innovation was presented by Jimin Chen of Beijing University of Technology (9738-37) Thursday afternoon.

At their 3D printing center, which opened in 2013, Chen and his research group are 3D printing customized, patient-specific surgical guide templates to aid in the placement of radiotherapy treatment seeds.

For this treatment, small 1mm diameter, 4.5mm long radioactive sources (125I) are implanted into tumors in quantities and distributions designed to localize radiation dose to the diseased region. By using the data provided by the CT scan, a 3D-printed template can be produced that sits directly on the skin surface and has marked insertion sites, as opposed to a universal, nonconforming plate. Not only does this increase the surgical precision of placement, but it also reduces the amount of time required for the procedure.

3D printing technology is becoming a large market in medicine, with at least four levels of application:

  • printing of models for surgical planning or training
  • printing of templates or tools for surgical assistance
  • printing parts for implant
  • perhaps 10-15 years down the road, possibly even printing organic tissues directly.

Chen was eager to remind the audience that talented people are urgently needed in this cross-disciplinary area of research.


All photos © SPIE, the international society for optics and photonics, except where noted. Contact for images or permissions.

Contributors: Jacqueline Andreozzi, Khushi Vyas

SPIE Photonics West

13-18 February 2016
San Francisco, California, USA


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