This PDF file contains the front matter associated with SPIE Proceedings Volume 11724, including the Title Page, Copyright information and Table of Contents

Diode lasers emitting at longer wavelengths between 1500 nm and 2500 nm open a wide range of defence applications as compact and efficient light sources in the fields of infrared countermeasures (IRCM), light detection and ranging (LIDAR) at so-called eye-safe wavelengths, or pumping of solid-state and optically pumped semiconductor lasers emitting in the 2-4 μm regime. Whereas for wavelengths below 1850 nm, InGaAsP/InP is naturally predestined for highpower diode lasers, beyond 1900 nm the GaSb-based (AlGaIn)(AsSb) material system offers clear advantages compared to InP-based diode lasers in terms of output power and wall-plug efficiency. Beside high output power, most of the applications request high beam quality. This so-called brightness can be realized in a cost-efficient and compact way by the tapered resonator concept which has been successfully established already in the 1 μm wavelength regime. For three specific wavelengths (1.5μm, 1.9μm, 2.3μm), broad-area lasers with 100 μm stripe width as well as 1 mm long ridge-waveguide lasers have been processed. Based on these results, an optimized resonator geometry has been derived for tapered devices aiming 1 W in CW operation and 2W in pulsed mode. For narrow-linewidth operation, the tapered devices are provided with anti-reflection coatings of less than 0.01% on both facets and can be spectrally stabilized with an external grating. Beside the electro-optical characterization, beam quality has been characterized in terms of near field and far field distribution and M2.

‘Space-time’ (ST) wave packets are propagation-invariant pulsed optical beams whose group velocity can take on arbitrary values in free space. Such unique behavior is a consequence of tight spatio-temporal spectral correlations introduced into the field, which in turn results in a correlation between the temporal bandwidth and numerical aperture. Utilizing large temporal bandwidths or creating ultraslow group velocities both require excessively large numerical apertures. We introduce a methodology for spectral recycling that circumvents this obstacle, and confirm experimentally that the unique characteristics of the ST wave packet are retained. Furthermore, we synthesize a ST wave packet having a group velocity of c/14.3 at a low numerical aperture by exploiting spectral recycling.

Refraction of an optical beam is a spatial phenomenon involving changes in the wave momentum while conserving energy. Although Snell’s law applies to monochromatic plane waves, its consequences are generally extended to a pulsed beam with an implicit assumption of separability of spatial and temporal degrees of freedom. Certain expectations are built into the law of refraction – that the speed of the transmitted light pulse is solely determined by the refractive index, hence independent of the angle of incidence to the interface. Here we show that introducing spatio-temporal correlation into a pulsed beam unveils a remarkable refractive phenomenon – tunable group velocity by varying angle of incidence. We present theoretical formulation as well as the experimental demonstration of this remarkable behavior by making use of 'space-time' wave-packets – propagation-invariant pulsed beam endowed with tight correlations between spatial and temporal frequencies.

We introduce a new effect that we call the ‘space-time’ (ST) Talbot effect in which an optical field lattice that is periodic in both space and time undergoes periodic axial revivals after propagation in free space. Although the purely spatial and purely Talbot effects have been observed separately in optics, they have not been realized simultaneously due to the disparity between the spatial and temporal Talbot lengths. Indeed, the temporal Talbot effect has been observed to date in only single-mode fibers. By identifying a new pulsed beam configuration that we call a V-wave whose diffraction and dispersion lengths are intrinsically equal, we obtain a periodic spatio-temporal lattice by discretizing the spatio-temporal spectrum of a V-wave, and consequently observe the first example of self-imaging in space and time using an optical field.

Space-time (ST) wave packets are propagation-invariant pulsed beam endowed with a tight correlation between the underlying spatial and temporal frequencies. We present a theoretical formulation and experimental demonstration of sub-millimeter incoherent ST light sheets traversing 110 m without significant diffraction. We synthesize ST fields of beam width ~ 0.7 mm from a superluminescent diode with a bandwidth of ~20 nm centered at 840 nm and observe propagation-invariant behavior across a distance of over 100-m distance in free-space. Finally, we study the effect of the aperture on the propagation distance and far-field beam size of ST light sheets.

The blue laser diode technology that is now emerging as the next generation high power laser source when evaluated at the system level has several distinct advantages over the infrared lasers making it an interesting candidate for high power laser development. Blue laser diodes are capable of operating at high temperatures (80C) which is a major advantage when determining the system’s size weight and power, and the shorter wavelength has a higher absorption characteristic than the infrared on all materials reducing the energy on target required to destroy the target. There are two main issues associated with using a high-power blue laser as a directed energy weapon, 1) the atmospheric transmission is challenging, especially at sea level and 2) the blue wavelength is not considered an eye safe wavelength. This paper will address the maturity of the blue laser technology, what the system operating parameters would be and the system performance under a range of atmospheric conditions. Initial studies indicate that a blue laser weapon system will indeed be very effective under a wide range of operating conditions.

Transparent ceramic fabrication via solid state sintering is opening a path to a new category of laser gain media with tailor-made doping and index profiles. Techniques such as assembly of green structure pieces, direct ink writing, and Ink jet printing allow the fabrication of a wide variety of tailored optics including; slabs, rods, gradient doping, thin disks, ceramic-clad single-crystal fibers, and planar waveguides. The potential for 3D printed gain media to have a profound impact on new laser design and integrated optics is yet untapped. This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-816729

Extending solid-state laser technology to longer wavelengths is difficult because the transitions that lead to mid-IR emission experience strong competition from the multiphonon-relaxation (MPR) which reduces the emission quantum efficiency. In this work, a comparative study of mid-IR (3-5 μm) spectroscopic properties on RE³⁺ ions doped in various low-phonon fluoride and chloride based crystals were explored. Obtained experimental results, including temperature dependent absorption and fluorescence, transition cross-sections, and fluorescence dynamics are discussed and the potential for efficient laser operation is evaluated. Ultimately, the chloride materials demonstrated more favorable laser parameters than the fluoride materials, including significantly longer upper laser level lifetimes.

The increased interest in lasers operating in the mid-infrared spectral region has prompted the development of new gain materials with low maximum phonon energy. Fluorites (calcium fluoride [CaF2], strontium fluoride [SrF2], and barium fluoride [BaF2]) have emerged as promising laser host crystals due to their low phonon energies, high thermal conductivities, and ability to incorporate RE dopants. Dy3+ has been studied in CaF2 and SrF2 but its spectroscopic properties are largely unexplored in BaF2. In this work, dysprosium-doped barium fluoride was explored for its mid-infrared laser potential in the 3-μm spectral region. Results of absorption and fluorescence measurements were used to generate stimulated-emission cross sections, and the gain characteristics were determined at both room temperature and 77 K.

There are only a few commercially available nonlinear optical materials in the spectral window of 3-20 μm, creating technological gaps that require new materials to address them. Alkali-metal chalcoarsenates (AAsQ2) are a promising class because of their high second harmonic generation (SHG) coefficients with γ-NaAsSe2(d33 = 169 pm/V) and β-LiAsS2(d33 = 98 pm/V). The AAsQ2 (A = Li, Na and Q = S, Se) compounds are made up of 1-dimensional (1/∞)[AQ2]— chains, connected by pyramidal AQ3 units as observed in the two structures. The chains are parallel and engage in inter-chain interactions via long As···Se contacts. γ-NaAsSe2 (Pc) undergoes a phase transition to the centrosymmetric δ-NaAsSe2 (Pbca) upon melting, making it a challenge to grow large single crystals for NLO applications. Here we report the crystal growth of γ-NaAsSe2 and β-LiAsS2 used for single crystal SHG measurements. We studied the structural effects of substituting with Na atoms with K in γ-NaAsSe2.

The γ-NaAsSe2 has attracted much attention as the next-generation infrared (IR) nonlinear optical (NLO) crystal. It has demonstrated one of the highest second harmonic generation (SHG) efficiencies as polycrystal. However,the full optical properties of single crystal have not been studied yet, which is required to understand its potential for future IR laser applications. Here, its linear and nonlinear optical properties are examined using spectroscopic ellipsometry and optical second harmonic generation (SHG).

We present the performance of a thulium:holmium-codoped fiber amplifier operating at 2050 and 2090 nm signal wavelength. This amplifier is built with polarization-maintaining fibers and is clad-pumped at 793 nm. We demonstrate more than a watt of signal power for both signal wavelengths. We compare the performance of this amplifier with a previously developed holmium-doped fiber amplifier operating at the same signal wavelengths. The amplifiers are compared in view of their optical-to-optical efficiency, optical bandwidth, gain, and noise figure.

Hollow core fibers have been investigated for several use cases relating to both single mode and multi-mode operation. Single mode, low-loss operation is a desired commodity in telecommunications and high-power delivery applications. Hollow core fibers can be designed with a structure that guides multiple modes in the core at low loss while also exhibiting strong stress sensitivity. In these anti-resonant hollow core fibers, perturbations to the structure such as micro-bending can efficiently couple core guided modes in short sections of fiber. This high sensitivity to structural distortion can be exploited for higher order mode generation, sensing, and for developing multimode nonlinear light sources. This work presents an investigation on using anti-resonant hollow-core fibers as a higher-order mode converter by inducing mechanical stress on the structure of the fiber.

Coherent light sources in the short- and mid-wave infrared spectral regions have many applications. We introduce a compact, hollow core fiber-based, quasi-phase-matched, electric field induced optical parametric amplifier (OPA). We numerically and analytically compute the spatially varying electrostatic fields within the pressurized xenon-filled core, which result from patterned electrodes with modulated voltages. We incorporate electrostatic fields, numerically modeled fiber transmission, and voltage thresholds into high fidelity modeling of OPA conversion efficiency. The required tens of meters of fiber are wrapped between two concentric cylinders printed with electrodes for experimental characterization of the OPA design.

Today, industry is accelerating the use of laser technologies. Laser technologies are one of the areas of material machining with high-energy energy flows. This actualizes monitoring of the performance of laser technologies, because it creates the preconditions for similar research in other areas. In this article, we present the results of experiments that make it possible to determine relationships between the vibroacoustic signals accompanying the action of laser pulses on a workpiece, and the intensity and duration of individual pulses. Analysis of experimental data has lead to identification of the main mechanisms of the formation of wave processes in the workpiece exposed to laser pulses and became the foundation for assessing the role of sublimation processes. The results obtained in this work can be used to develop monitoring system of laser processing for use in automated control systems.