Hagop Injeyan

Coherent combination of high-power, zigzag slab lasers

We demonstrate a scalable architecture for a high-power, high-brightness, solid-state laser based on coherent combinations of master oscillator power amplifier chains. A common master oscillator injects a sequence of multikilowatt Nd:YAG zigzag slab amplifiers. Adaptive optics correct the wavefront of each amplified beamlet. The beamlets are tiled side by side and actively phase locked to form a single output beam. The laser produces 19 kW with beam quality <2x diffraction limited. To the best of our knowledge, this is the brightest cw solid-state laser demonstrated to date.

Yb:YAG power oscillator with high brightness and linear polarization

A diode-pumped Yb:YAG laser with a novel end-pumped zigzag slab architecture has been developed. This architecture provides uniform transverse pump profiles, conduction cooling of the laser crystal, mechanical robustness, and ready scalability to higher powers. At room temperature the laser emits 415 W of cw power with 30% optical conversion efficiency. An image-inverting stable resonator permits a high-brightness output of 252 W with linear polarization and an average M(2) beam quality of 1.45. Q-switched pulse energies of as much as 20 mJ and average Q-switched powers of as much as 150 W were obtained while M(2) was maintained at <1.5.

Joint high power solid state laser program advancements at Northrop Grumman

Northrop Grumman Corporation has made significant progress in the development of compact, high power, continuous operation solid state lasers for military applications during the past six years. The Joint High Power Solid State Laser (JHPSSL) program is nearing completion of its third phase; its key objective is to demonstrate a 100kW solid state laser with excellent beam quality. Northrops unique scalable architecture coherently combines modular 15kW lasers to produce power levels of 100kW and beyond with excellent beam quality and run times. This paper describes the JHPSSL program history, Northrops high power solid state laser architecture and our demonstrated results.

Multi-kW near-diffraction-limited single-frequency Nd:YAG laser

Northrop Grumman is developing a laser architecture that can scale to >100 kW with a near-term goal of a 25 kW demonstration. The near-term 25 kW design is based on two chains of four slab amplifiers that produce average power of 12.5 kW each. Adaptive optics sense the output wavefront and piston relative to a reference, then adjust the phase of the master oscillator input to each chain to keep the wavefronts of each chain uniform and in phase. To reach the goal of 12.5 kW per chain, Northrop has demonstrated power scaling of individual amplifiers by extracting 4.5 kW form a single amplifier using a multimode resonator. This is well above the minimum needed to achieve 12.5 kW from a four-amplifier chain.

High Power Conversion to Mid-IR Using KTP and ZGP OPOs

A high average power, OPO based system has been developed for the purpose of generating output in the 2 - 5 µm mid-IR band. The system uses a cw diode array - pumped, Nd:YAG master oscillator power amplifier (MOPA) as the pump source and two tandem OPOs for wavelength conversion to the mid-IR. A Type II degenerate KTP OPO was used to convert the pump beam to 2.13 µm and a Type I near degenerate zinc germanium phosphite (ZGP) OPO was used to generate broadband radiation in the 3.7 - 4.1 and 4.4 - 4.8 µm wavelength range.

High average power Yb:YAG end-pumped zig-zag slab laser

A diode-pumped Yb:YAG laser has been developed with a novel end-pumped zig-zag slab architecture. In cw operation the laser emitted 415 W multimode and 228 W with linear polarization and average M2 beam quality of 1.35.

Active Tracker Laser (ATLAS)

A phase conjugated Nd:YAG amplifier has demonstrated 690 W average power and 1.1 ×DL beam quality. The frequency doubled output was 175 W at 1.5 ×DL and 45% conversion efficiency. This is the highest average green power and highest average brightness reported.

One Joule Per Pulse, 100 Watt, Diode-Pumped, Near Diffraction Limited, Phase Conjugated, Nd:YAG Master Oscillator Power Amplifier

We have assembled and tested a diode-pumped, phase conjugated Nd:YAG master oscillator power amplifier (PC MOPA) operating at an average power of 100 Watts. 1 J per pulse has been extracted at a repetition rate of 100 Hz with a beam quality (BQ) of 1.1 x diffraction limited (D.L.). This combination of average power and beam quality makes this the brightest short pulse solid-state laser reported to date. The optical efficiency of 22% and the overall efficiency of 9.4% also represent record performance for high energy short pulse lasers. Excellent spatial uniformity and a pulse length of 7 ns make this laser ideal for frequency doubling and parametric conversion.

Diode-pumped Nd:YAG laser for precision laser machining

Results are presented on a high power, diode‐pumped, pulsed Nd:YAG laser for precision laser machining. The laser is an unstable resonator with a graded reflectivity outcoupler, generating a beam with excellent beam quality. The gain medium is a single zig‐zag slab, pumped symmetrically by diode arrays. The use of diode arrays minimizes the thermal loading on the slab, and the zig‐zag path averages thermal distortions in the zig‐zag dimension. Measurements of beam divergence as a function of diode duty‐cycle will be presented. Available pulse formats will also be discussed. To date, the laser has produced 720 W at 20% diode duty‐cycle with a stable cavity and 550 W at 20% duty cycle with an unstable cavity in close agreement with model predictions. The beam divergence has been measured to be 1.7 times diffraction‐limited at 20% duty cycle. The laser has been operated with pulse lengths from 20 μs to 1 ms and is being used to obtain laser processing data, with some results shown.

Diode-array-pumped kilowatt laser

The Diode Array Pumped Kilowatt Laser (DAPKL) has demonstrated more than an order of magnitude increase in brightness and average power for short pulse diode-pumped solid-state lasers since its inception in 1991. Significant advances in component technology has been demonstrated, including development of a diffusion bonding process for producing large slabs of Nd:YAG laser material. Phase conjugation by stimulated Brillouin scattering has been demonstrated with high reflectivity and fidelity in a simple focused geometry with input powers of 100 W. Pulse energies at 1.06 μm of up to 10 J per pulse have been demonstrated with a beam quality of 1.25 times diffraction limited at 33 Hz. An average power of 940 Watts at 100 Hz has been obtained with two times diffraction limited beam quality. Efficient frequency doubling with an average power of 165 W has been demonstrated with 5 J per pulse at 0.53 μm. The system has been packaged in a compact brassboard for long term stability and reliability of operation.