Continuous-wave and passively Q-switched cladding-pumped planar waveguide lasers.

Greater than 12 W of average output power has been generated from a diode-pumped Yb:YAG cladding-pumped planar waveguide laser. The laser radiation developed is linearly polarized and diffraction limited in the guiding dimension. A slope efficiency of 0.5 W/W with a peak optical-optical conversion efficiency of 0.31 W/W is achieved. In a related structure, greater than 8 W of Q -switched average output power has been generated from a Nd:YAG cladding-pumped planar waveguide laser by incorporation of a Cr(4+): YAG passive Q switch monolithically into the waveguide structure. Pulse widths of 3 ns and pulse-repetition frequencies as high as 80 kHz have been demonstrated. A slope efficiency of 0.28 W/W with a peak optical-optical conversion efficiency of 0.21 W/W is achieved.

Consideration of Stimulated Raman Scattering in Yb:Sr(5)(PO(4))(3)F Laser Amplifiers.

The stimulated Raman-scattering (SRS) gain coefficient has been measured quantitatively for the first time to our knowledge in Yb:Sr(5)(PO(4))(3)F to be 1.23 ? 0.12 cm/GW at 1053 nm. These data, along with surface and bulk losses, feedback that is due to surface reflections, gain saturation, and bandwidth, have been applied to a quantitative model that predicts the effects of SRS within a laser amplifier system where the laser gain media show SRS gain. Limitations and impact to the laser amplifier performance are discussed, along with possible techniques to reduce SRS loss.

Three-level Q-switched laser operation of ytterbium-doped Sr(5)(PO(4))(3)F at 985 nm.

Ytterbium-doped Sr(5)(PO(4))(3)F was successfully lased at 985 nm in quasi-cw mode with a slope efficiency of 74% and an absorbed threshold energy of 18 mJ. Q-switched slope efficiencies of 21% were obtained with a maximum energy of 9.4 mJ in 8.8-ns pulses.

High-power dual-rod Yb:YAG laser.

We describe a diode-pumped Yb:YAG laser that produces 1080 W of power cw with 27.5% optical optical efficiency and 532 W Q-switched with M(2)=2.2 and 17% optical-optical efficiency. The laser uses two composite Yb:YAG rods separated by a 90 degrees quartz rotator for bifocusing compensation. A microlensed diode array end pumps each rod, using a hollow lens duct for pump delivery. By changing resonator parameters we can adjust the fundamental mode size and the output beam quality. Using a flattened Gaussian intensity profile to calculate the mode-fill efficiency and clipping losses, we compare experimental data with modeled output power versus beam quality.

183-W, M(2) = 2.4 Yb:YAG Q-switched laser.

We have fabricated a diode-array end-pumped Yb:YAG rod laser with output powers greater than 200 W cw and 195 W Q -switched at 5 kHz. At an output power of 183 W and a repetition rate of 5 kHz, the beam quality was measured to be M(2)=2.4 . The laser design incorporates a hollow lens duct to concentrate the diode pump light for delivery to the end of the laser rod while maintaining access to the laser beam. This configuration provides increased flexibility for the resonator design and permits the use of birefringence compensation in the cavity to yield polarized output with increased efficiency. Using the recently described birefringence compensation method of Clarkson et al. [in Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C., 1998), paper CTuI3], we obtained 112 W of cw power with a polarized beam of M(2)=3.2.

Analysis of an intracavity-doubled diode-pumped Q-switched Nd:YAG laser producing more than 100 W of power at 0.532 microm.

A diode-pumped Nd:YAG laser was frequency doubled to 0.532 microm with an intracavity KTiOPO(4) crystal in a V-cavity arrangement, achieving an output power of 140 W. Acousto-optic Q switching was employed at repetition rates of 10-30 kHz, and the beam quality was assessed at M(2) approximately 50. It was deduced on the basis of our model that the strength of the nonlinear frequency conversion is the main parameter determining the pulse width.

1.1-W cw Cr:LiSAF laser pumped by a 1-cm diode array.

We demonstrate 1.1-W cw output power from a diode-laser array-pumped Cr:LiSAF laser based on a concept that allows for pumping low-gain solid-state lasers at reduced temperature rise. We discuss scaling to higher powers as a function of diode power and define a figure of merit for evaluating given diode lasers as pump sources for low-gain solid-state lasers.

Theory and optimization of lens ducts.

Lens ducts are simple optical devices that have found application in the coupling of pump radiation from extended two-dimensional semiconductor laser diode arrays into solid-state laser gain media. The operation of these devices relies on the combined effects of lensing at their curved input surface and channeling by total internal reflection off their canted planar sides, to contain and couple semiconductor diode laser light efficiently to the input face of a solid-state laser crystal or glass. The lens duct provides a robust method for amplifying the irradiance of laser diode array pump sources and has made possible a scalable diode end-pumping architecture that offers the opportunity to expand significantly the number of ions and transitions that can be practically engaged in diode-pumped solid-state laser systems. An analytic model that describes the transfer efficiency of lens ducts and aids in the optimization of their design is presented.

1-W average power levels and tunability from a diode-pumped 2.94-microm Er:YAG oscillator.

A tunable Er:YAG laser, side pumped by a quasi-cw InGaAs diode array, generates > 500 mW of power at 2.936 microm. The cavity is a 4-cm plano-concave resonator that uses total internal reflection on the pump face of the Er:YAG crystal to couple the diode emission into the resonating modes of the oscillator. Tuning is accomplished by angle tuning a 300-microm-thick YAG étalon. The tuning range is 2.933-2.939 microm. Thermal lensing limits the duty factor to 4% or 8%, depending on the Er:YAG crystal thickness (2 or 1 mm). A 2.5-cm-long resonator operates at an 11% duty factor and generates 1.3 W of average power.

Properties of Cr:LiSrAIF(6) crystals for laser operation.

We have performed several physical and optical measurements on the Cr:LiSAF (LiSrAlF(6)) laser material that are relevant to its laser performance, including thermal and mechanical properties, water durabilities, and Auger upconversion constants. The expansion coefficient, Young's modulus, fracture toughness, thermal conductivity, and heat capacity are all used to determine an overall thermomechanical figure of merit for the crystal. An investigation of the water durability suggests that the cooling solution should be maintained at pH = 7 to ameliorate problems associated with water dissolution. The Auger constant was found to become much more significant at higher Cr doping, in which excited-state migration leads to a substantial increase in the upconversion rate. We propose a design for a 50-W Cr:LiSAF laser system that is based on a detailed knowledge of all the relevant material parameters.

Laser driver for soft-x-ray projection lithography.

A design of a diode-pumped Nd:YAG laser for use as the driver for a soft-x-ray projection lithography system is described. This laser will output up to 1 J per pulse with a 2- to 5-ns pulse duration and a 400-Hz pulse repetition rate. The design employs microchannel-cooled diode laser arrays, zigzag slab energy storage, a regenerative amplifier cavity that uses phase conjugator beam correction for near-diffraction-limited beam quality, and stimulated Brillouin scattering pulse compression to achieve the required pulse length.