The utility of military mid-IR lasers, particularly in the area of countermeasures, is well understood and practical laser
systems have been fielded which currently provide protection to a wide number of military platform types. Technical
performance, efficiency and power for these lasers, has driven current production designs to utilise diode pumped solid
state lasers (DPSSLs) with wavelength conversion through non-linear crystals. In this paper, we review the development
of laser technologies which have potential to form the basis of the next generation of IRCM lasers, in particular, fibrepumped
solid state lasers, optically pumped semiconductor lasers (OPSLs) and quantum cascade lasers (QCLs). Moreover, this review will focus on the relative merits of the technologies for engineering and productionisation of a military laser system, and address those issues most relevant for design and manufacture for the military environment. These include not only technical performance, power and efficiency, but also thermal management, mass, volume, cost and overall complexity for manufacture.

Development of Military Lasers for Optical Countermeasures in the Mid-IR

Performance requirements for laser sources, operating in the mid-IR, providing protection of airborne platforms from heat-seeking missiles are reviewed. The critical performance charact eristic for a countermeasures laser is useful energy on target, which requires the laser to generate high brightness output in the appropriate spectral bands with rapid turn-on time. Integration with a comp act beam director places an upper limit on th e beam quality of the laser output. The key driver for the detailed laser design is to maximise the overall wallplug efficiency in order to minimise the complexity and volume, in turn maximising the reliability and reducing the cost. In particular routes to reduce the thermal management system for the laser produce the single largest improvement in overall wallplug efficiency, with the ultimate goal of realising a truly athermal laser. Candidate technologi es for IR countermeasures lasers are briefly reviewed. Keywords: IRCM laser, thulium fibre laser, Ho:Y AG laser, OPO, ZGP, OPGaAs, OPSL, QCL

Performance Requirements for Countermeasures Lasers

A quasicontinuous tuning range of 65 nm at 3.2 μm was obtained for continuous wave, single-longitudinal-mode operation at 77 K of an optically pumped distributed-feedback laser with a chirped grating. Interferometric lithography with spherical wavefronts was used to fabricate a large-area chirped grating whose period varied continuously in the direction of the grating lines. Tuning was achieved by translating the optical pump stripe relative to the device to activate regions with different grating periods. Methane absorption spectra, obtained using this tunable distributed-feedback laser, closely match the high-resolution transmission molecular absorption database simulations.

Widely tunable distributed-feedback lasers with chirped gratings

We explore the accessible wavelength range offered by InP/AlGaInP quantum dots (QD)s grown by metal–organic vapour phase epitaxy and explain how changes in growth temperature and wafer design can be used to influence the transition energy of the dot states and improve the performance of edge-emitting lasers. The self assembly growth method of these structures creates a multi-modal distribution of inhomogeneously broadened dot sizes, and via the effects of state-filling, allows access to a large range of lasing wavelengths. By characterising the optical properties of these dots, we have designed and demonstrated dual-wavelength lasers which operate at various difference-wavelengths between 8 and 63 nm. We show that the nature of QDs allows the difference-wavelength to be tuned by altering the operating temperature at a rate of up to 0.12 nm K−1 and we investigate the factors affecting intensity stability of the competing modes.

https://iopscience.iop.org/article/10.1088/0268-1242/30/4/044002/pdf

Exploring the wavelength range of InP/AlGaInP QDs and application to dual-state lasing

We present a study of a dual wavelength optically pumped midinfrared semiconductor laser. In order to control the outcoupled power of each wavelength, the modal overlap between the adjacent gain regions was minimized while the pump absorbance for each gain region was balanced. The nominal power expectation, based solely on the absorbed power per gain region, was observed to be generally in good agreement with measurement. Improved power accounting can be accomplished if the waveguide loss and internal efficiency at each operational wavelength is known.

Controlling the outcoupled power in a dual wavelength optically pumped semiconductor laser

We demonstrate optically pumped semiconductor lasers that are capable of simultaneously emitting at two different midinfrared wavelengths. The wavelengths can be independently chosen and designed into the heterostructure. The epitaxial III-V antimonide structure employs two sets of type-II quantum wells in a waveguide that is partitioned by a thin electrical barrier that is transparent to the pump radiation. Two-color devices emitting at wavelengths as far apart as ~4.0 and ~5.4 mum are reported.

Optically Pumped Midinfrared Laser With Simultaneous Dual-Wavelength Emission

An optically pumped edge-emitting semiconductor laser emitting near 4.1 μm was designed with weak transverse mode confinement resulting in an exceptionally large transverse optical mode size. Consequently, a laser device is reported that exhibits a fast-axis divergence angle of ~4.2° full-width at half-maximum (FWHM). More notably, a large reduction of the lateral axis divergence is also observed as a result of the increased lateral coherency. The reduced confinement factor and differential gain serves to suppress lateral filamentation. Despite the higher threshold and lower power, a lateral divergence angle of ~3.2° FWHM and increased lateral brightness is achieved.

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Ultralow Beam Divergence and Increased Lateral Brightness in Optically Pumped Midinfrared Laser

We describe high peak-power, broad area mid-infrared semiconductor lasers. The laser structures incorporated 14 type-II quantum wells imbedded in thick waveguide/absorber regions composed of InGaAsSb. The Fabry-Perot lasers were optically pumped with the output from a passively-Q-switched Ho:YAG laser capable of delivering 100 kW at 2.09 um. The emission from the optically pumped semiconductor laser (OPSL) was near 4.1 um. The emission was spectrally and temporally resolved and showed evidence for the creation of a hot-carrier population at the higher pump powers. A roll-over in the OPSL output power curve was observed at pump-powers greater than ∼20 kW. The maximum single-ended OPSL power was near 470W.

High-peak power from optically-pumped mid-IR semiconductor lasers

In this paper, we briefly review optically pumped type-II "W" quantum-well semiconductor lasers that emit in the midinfrared
wavelengths. In addition, we demonstrate on-chip unstable resonator cavity devices that exhibit excellent lateral
beam quality.

High performance optically pumped antimonide mid-infrared lasers

The molecular beam epitaxy of advanced heterostructures containing mixed arsenide/ antimonide layers presents a number of special challenges. A 5 /spl mu/m thick laser designed to emit mid-infrared radiation of 4 /spl mu/m wavelength, for example, may incorporate thick (/spl sim/2 /spl mu/m) lattice-matched AlGaAsSb layers for optical confinement, thinner (/spl sim/0.1 /spl mu/m) lattice-matched InGaAsSb layers for electrical confinement, and extremely thin (/spl sim/20 /spl Aring/) InAs and InGaSb layers as quantum wells. Such structures highlight the need for precise control of alloy composition over time on the one hand, and reproducible manipulation of the interfacial chemistry across very thin III-As and III-Sb layers on the other.

G. C. Dente

Papers

Optically Pumped Midinfrared Laser With Simultaneous Dual-Wavelength Emission

Ultralow Beam Divergence and Increased Lateral Brightness in Optically Pumped Midinfrared Laser

High-peak power from optically-pumped mid-IR semiconductor lasers

High performance optically pumped antimonide mid-infrared lasers

Modulated beam growth and interface control in III-AsSb laser heterostructures