Dennis D. Lowenthal

High-power laser source with spectrally beam-combined diode laser bars

Aculight has demonstrated spectral beam combining of four diode laser bars in a single optical cavity; each 1 cm wide diode bar included 200 individual single mode laser emitters. The beam combining was accomplished in the plane of the diode bar -- slow direction. In earlier work, Aculight has reported near diffraction limited performance from single diode laser bars where we have spectrally beam combined 200 laser emitters while maintaining a beam quality near the diffraction limit. Without spectral beam combination these diode laser bars will have a beam quality, in the plane of the bar, corresponding to an M2 of 1000. In current work, Aculight is extending this technology to demonstrate a spectrally beam combined, diode laser system of 50 Watts, with near diffraction limited beam quality. To accommodate multiple diode laser bars, optical modeling was used to design and complete sensitivity analysis of a unique optical cavity based on the Schmidt telescope principal to remove off-axis aberrations. Error trees have been developed for beam quality and efficiency that illustrates just how the efficiency and beam quality have been maintained within this system.

Solid state lasers for 193-nm photolithography

Advances in technology now make possible solid-state 193 nm lasers. Solid-state can operate with pulse repetition rates of > 10 kHz, minimizing peak-power damage to stepper optics. Furthermore, solid-state lasers are potentially more reliable and could have lower operating costs than ArF excimer lasers. Achievement of spectral linewidths < 0.1 pm for use with refractive lens systems is straightforward in solid-state laser systems. Ultraviolet solid-state laser technology is much less mature than excimer laser technology; so while there is far to go, there is much more potential for rapid progress in solid-state lasers than in excimer lasers. Aculight has begun a program to develop a multiwatt, 10 kHz solid-state 193 nm laser. Although efficient conversion from 1064 nm to 193 nm is easier for high peak power pulses, minimization of lens damage requires low peak power. Eventual goals for the technology are to achieve output powers 10 - 20 W at > 20 kHz repetition rate in > 10 ns pulses, limiting peak powers to < 200 kW. High pulse repetition rates will permit excellent dose control, and facilitate decoherence of the high-coherence beam from the solid-state laser system.

Novel cavity design for a high-efficiency, high-energy near-infrared β-BaB 2 0 4 parametric generator

In this paper, we report on a novel cavity design for optical parametric generators that removes the cavity mode constraints present in conventional parametric oscillators. A conversion efficiency of 30% is obtained in a 532-nm pumped BBO oscillator using this design.

Efficient mid-infrared conversion technologies

Average power scaling of mid-infrared Optical Parametric Oscillators are presently limited by nonlinear material bulk absorption and resulting thermal gradients and thermally induced focusing and higher order aberrations. We discuss an optical correction scheme that corrects higher order aberrations typically present in gaussian intensity profile beams used for pumping OPOs to reduce the nonlinear dephasing by one- half. While correction of thermal focus has been shown to improve the power scaling in an OPO, further improvements can be made by correcting the remaining higher order aberrations. Such reduction in dephasing should significantly improve the power scaling potential of solid state lasers and OPOs.

Fully stabilized single-frequency Ti:Al2O3 laser oscillator

Single-longitudinal-mode (SLM), pulsed operation is demonstrated on a tunable Ti:Al2O3 oscillator that utilizes a glancing-incidence cavity configuration. The oscillator is tunable over 720-915 nm, and the output has a bandwidth that is near transform-limited at equal to or less than 500 MHz. Beam walk-off and diffraction effects define cavity configurations for which SLM operation is possible. Stable SLM operation, without any active stabilization, is achieved with a 6.5-cm long cavity in which the separation between the tuning mirror and the grating is kept small (1.5 cm). The oscillator is actively stabilized by a feedback mechanism that monitors small changes in the direction of the output beam that result from small wavelength deviations. Single-longitudinal-mode operation over several hours has been demonstrated. The temporal jitter of the oscillator is reduced to + or - 1.2 ns while maintaining SLM operation.

Optical Parametric Oscillator-Based Laser Source Continuously Tunable from 250 to 400 nm

Efficient generation of ultraviolet radiation tunable over the 240-410 nm range has been achieved in a practical, effective system. The signal or idler from an Optical Parametric Oscillator/Amplifier tuning in the 0.7-2.1 μm range is mixed with the second or third harmonic from a Nd:YAG laser to produce approximately 30 mJ of ultraviolet output.

Ti:Al2O3 laser amplifier design study

In this work, the issues of broadband tuning in the design of a high average power Ti:Sapphire amplifier for a chromatic scanning lidar system are addressed. A novel pump delay and staging scheme is used to maintain high extraction efficiency with flat temporal and spatial pulse profiles while tuning over a 700-900 nm range. The effects of the chromatic scanning scheme on ASE suppression and beam pointing are discussed in relation to the amplifier optical system. The average power scaling for three power amplifier geometries (zigzag slabs, parallel plates, and active mirrors) was investigated to determine the limitations of each. Pump light is provided by diode laser-pumped Nd:GGG slab lasers which make up over 60 percent of the system weight. Predicted electrical to light laser efficiency was 3-4 percent over the wavelength tuning range.

Diode-End-Pumped, Q-Switched Nd:YLF Laser

A Q-switchedNd:YLF laserpumped by two quasi-cw diode laser bars has been developed. The laser produces 5-mJ, 12- ns pulses at 1.047 μm, and has been frequency doubled and quadrupled to 1.5 mJ and 0.35 mJ, respectively. Repetition rates of 500 Hz will be attainable when driven by 20% duty factor diode laser bars.