Mark Weber

IRCS : Infrared Camera and Spectrograph for the Subaru Telescope

A 1-5 micrometers IR camera and spectrograph (IRCS) is described. The IRCS will be a facility instrument for the 8.2 m Subaru Telescope at Mauna Kea. It consists of two sections, a spectrograph and a camera section. The spectrograph is a cross-dispersed echelle that will provide a resolving power of 20,000 with a slit width of 0.15 arcsec and two-pixel sampling. The camera section serves as a slit viewer and as a camera with two pixel scales, 0.022 arcsec/pixel and 0.060 arcsec/pixel. Grisms providing 400-1400 resolving power will be available. Each section will utilize an ALADDIN II 1024 X 1024 InSb array. The instrument specifications are optimized for 2.2 micrometers using the adaptive optics and the tip-tilt secondary systems of the Subaru Telescope.

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.

Coherently coupled high-power fiber arrays

A four-element fiber array has demonstrated 470 watts of coherently phased, linearly polarized light energy in a single far-field spot. Each element consists of a single-mode fiber-amplifier chain. Phase control of each element is achieved with a Lithium-Niobate phase modulator. A master laser provides a linearly polarized, narrow linewidth signal that is split into five channels. Four channels are individually amplified using polarization maintaining fiber power amplifiers. The fifth channel is used as a reference arm. It is frequency shifted and then combined interferometrically with a portion of each channels signal. Detectors sense the heterodyne modulation signal, and an electronics circuit measures the relative phase for each channel. Compensating adjustments are then made to each channels phase modulator. This effort represents the results of a multi-year effort to achieve high power from a single element fiber amplifier and to understand the important issues involved in coherently combining many individual elements to obtain sufficient optical power for directed energy weapons. Northrop Grumman Corporation and the High Energy Laser Joint Technology Office jointly sponsored this work.

Diffractive-optics-based beam combination of a phase-locked fiber laser array

A diffractive optical element (DOE) is used as a beam combiner for an actively phase-locked array of fiber lasers. Use of a DOE eliminates the far-field sidelobes and the accompanying loss of beam quality typically observed in tiled coherent laser arrays. Using this technique, we demonstrated coherent combination of five fiber lasers with 91% efficiency and M2=1.04. Combination efficiency and phase locking is robust even with large amplitude and phase fluctuations on the input laser array elements. Calculations and power handling measurements suggest that this approach can scale to both high channel counts and high powers.

Brightness-Scaling Potential of Actively Phase-Locked Solid-State Laser Arrays

Recent progress in developing phased arrays of high-brightness solid-state lasers is summarized. We address the prospects for continued brightness-scaling via a model that extrapolates measured results to large numbers of array elements and provides a quantitative illustration of the features of coherent beam combination. This demonstrates that with present-day technology, both slab and fiber lasers have the capability to scale to unprecedented brightness levels.

Current performance and on-going improvements of the 8.2 m Subaru Telescope

An overview of the current status of the 8.2m Subaru Telescope constructed and operated at Mauna Kea, Hawaii, by the National Astronomical Observatory of Japan is presented. The basic design concept and the verified performance of the telescope system are described. Also given are the status of the instrument package offered to the astronomical community, the status of operation, and some of the future plans. The status of the telescope reported in a number of SPIE papers as of the summer of 2002 are incorporated with some updates included as of 2004 February. However, readers are encouraged to check the most updated status of the telescope through the home page, http://subarutelescope.org/index.html, and/or the direct contact with the observatory staff.

Coherently coupled high power fiber arrays

A four-element fiber array has demonstrated 470 watts of coherently phased, linearly polarized light. The results of this experiment as well as comparisons to other fiber array approaches will be presented

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 have been demonstrated, including: development of a diffusion bonding process for producing large slabs of Nd:YAG laser material. Phase conjugation by stimulated Brillouin scattering (SBS) has been demonstrated with high reflectivity and fidelity in a simple focused geometry with input powers of 100 W. Pulse energies at 1.06 /spl mu/m of 10 J have been demonstrated with a beam quality of 1.5 times diffraction limited at the 500-W level. An average power of 875 W at 100 Hz has been obtained. Efficient frequency doubling with a record power of 165 W has been demonstrated with 5 J per pulse at 0.53 /spl mu/m. Work is ongoing to enclose the system in a compact brassboard with improved performance and long term stability.

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.

Active tracker laser (ATLAS)

A high brightness diode-pumped, Nd-YAG solid state laser has been designed, fabricated, and tested. This phase conjugated master oscillator/power amplifier (MOPA) device produces 20-ns Q-switched pulses at 2500 Hz at an average power of 690 W and a beam quality of 1.1/spl times/DL when the pump diodes are operated at 27.5% duty cycle. With an external KTP doubler, this device has produced 175 W of green average power at a beam quality of 1.5 /spl times/ DL and a conversion efficiency of 45% over continuous operating times as long as one hour. This 1.06 /spl mu/m result is believed to be the highest average power brightness achieved, and the 532-nm performance is both the highest average green power and the highest average brightness ever reported.