Jay A. Skidmore

115-W Tm:YAG diode-pumped solid-state laser

A compact diode-pumped Tm:YAG laser capable of generating greater than 100 W of CW power at 2 /spl mu/m has been demonstrated. A scalable diode end-pumping architecture is used in which 805-nm radiation, coupled to the wing of the Tm/sup 3+3/H/sub 6/-/sup 3/H/sub 4/ absorption feature, is delivered to the end of the laser rod via a lens duct. To facilitate thermal management, undoped YAG end caps are diffusion bonded to the central doped portion of the laser rod. For 2% and 4% Tm-doped rods of the same length, the lower doping level results in higher power, indicating that cross relaxation is still efficient while offering lower thermal stress and reduced absorption at the laser wavelength. Output powers for various output coupler reflectivities are compared to the predictions of a quasi-three-level model. Thermal lensing, cavity stability, and stress-induced birefringence measurements are described. The beam quality was analyzed with the 2% Tm-doped rod and a flat output coupler, yielding M/sup 2/ values of 14-23.

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 M2=2.2 and 17% optical–optical efficiency. The laser uses two composite Yb:YAG rods separated by a 90° 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.

High-average-power 1-/spl mu/m performance and frequency conversion of a diode-end-pumped Yb:YAG laser

Using a diode-end-pumped technology, a Yb:YAG laser capable of delivering up to 434 W of CW power has been demonstrated. The system incorporates a unique composite rod design which allows for high-average-power operation while simultaneously suppressing parasitic oscillations. Modeling and experimental data to support the quenching of parasitics are discussed. Beam quality measurements for CW operation with several cavity configurations are presented. In particular, beam quality measurements at 340-W CW yielded a beam quality factor of M/sup 2/=21. Predictions of a quasi-three-level model are compared with the experimental data for several output coupler reflectivities. An observed dependence of the cavity mode fill as a function of output coupler reflectivity is discussed. Employing a single acoustooptical switch, the system was Q-switched at 10 kHz and generated output powers up to 280 W with a measured beam quality of M/sup 2/=6.8 at 212 W, With an external dual-KTP crystal configuration, the Q-switched output was frequency converted to 515 nm and produced up to 76 W at 10 kHz in a 30-ns pulse length.

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

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.

Diode-pumped ytterbium-doped Sr/sub 5/(PO/sub 4/)/sub 3/F laser performance

The performance of the first diode-pumped Yb/sup 3+/-doped Sr/sub 5/(PO/sub 4/)/sub 3/F (Yb:S-FAP) solid-state laser is discussed. An InGaAs diode array has been fabricated that has suitable specifications for pumping a 3/spl times/3/spl times/30 mm Yb:S-FAP rod. The saturation fluence for diode pumping was deduced to be 5.5 J/cm/sup 2/ for the particular 2.8 kW peak power diode array utilized in our studies. This is 2.5/spl times/ higher than the intrinsic 2.2 J/cm/sup 2/ saturation fluence as is attributed to the 6.5 nm bandwidth of our diode pump array. The small signal gain is consistent with the previously measured emission cross section of 6.0/spl times/10/sup -20/ cm/sup 2/, obtained from a narrowband-laser pumped gain experiment. Up to 1.7 J/cm/sup 3/ of stored energy density was achieved in a 6/spl times/6/spl times/44 mm Yb:S-FAP amplifier rod. In a free running configuration, diode-pumped slope efficiencies up to 43% (laser output energy/absorbed pump energy) were observed with output energies up to /spl sim/0.5 J per 1 ms pulse. When the rod was mounted in a copper block for cooling, 13 W of average power was produced with power supply limited operation at 70 Hz with 500 /spl mu/s pulses.

Silicon monolithic microchannel-cooled laser diode array

A monolithic microchannel-cooled laser diode array is demonstrated that allows multiple diode-bar mounting with negligible thermal cross talk. The heat sink comprises two main components: a wet-etched Si layer that is anodically bonded to a machined glass block. The continuous wave (cw) thermal resistance of the 10 bar diode array is 0.032 °C/W, which matches the performance of discrete microchannel-cooled arrays. Up to 1.5 kW/cm2 is achieved cw at an emission wavelength of ∼808 nm. Collimation of a diode array using a monolithic lens frame produced a 7.5 mrad divergence angle by a single active alignment. This diode array offers high average power/brightness in a simple, rugged, scalable architecture that is suitable for large two-dimensional areas.

High-power InAlGaAs-GaAs laser diode emitting near 731 nm

High-power, reliable operation of an InAlGaAs-based QW laser diode structure emitting near 731 nm and having a strained InAlGaAs active region is described. Threshold currents for coated 100 /spl mu/m/spl times/1000 /spl mu/m devices are 281 mA, and a peak power conversion efficiency of 41% is measured. Internal losses are measured to be 1.2 cm/sup -1/. A system for fiber-coupling two-dimensional continuous-wave (CW) arrays of these devices is demonstrated.

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.

High-average-power diode-pumped Yb:YAG lasers

A scaleable diode end-pumping technology for high-average- power slab and rod lasers has been under development for the past several years at Lawrence Livermore National Laboratory (LLNL). This technology has particular application to high average power Yb:YAG lasers that utilize a rod configured gain element. Previously, this rod configured approach has achieved average output powers in a single 5 cm long by 2 mm diameter Yb:YAG rod of 430 W cw and 280 W q-switched. High beam quality (M2 equals 2.4) q-switched operation has also been demonstrated at over 180 W of average output power. More recently, using a dual rod configuration consisting of two, 5 cm long by 2 mm diameter laser rods with birefringence compensation, we have achieved 1080 W of cw output with an M2 value of 13.5 at an optical-to-optical conversion efficiency of 27.5%2. With the same dual rod laser operated in a q-switched mode, we have also demonstrated 532 W of average power with an M2 less than 2.5 at 17% optical-to-optical conversion efficiency. These q-switched results were obtained at a 10 kHz repetition rate and resulted in 77 nsec pulse durations. These improved levels of operational performance have been achieved as a result of technology advancements made in several areas that will be covered in this manuscript. These enhancements to our architecture include: (1) Hollow lens ducts that enable the use of advanced cavity architectures permitting birefringence compensation and the ability to run in large aperture-filling near-diffraction-limited modes. (2) Compound laser rods with flanged-nonabsorbing-endcaps fabricated by diffusion bonding. (3) Techniques for suppressing amplified spontaneous emission (ASE) and parasitics in the polished barrel rods.

High-efficiency AlGaAs-based laser diode at 808 nm with large transverse spot size

Lasers diodes having a large transverse spot size have been fabricated from a modified graded index separate confinement heterostructure with an active region consisting of two 70 /spl Aring/ Al/sub 0.15/In/sub 0.10/Ga/sub 0.75/As strained quantum wells. The catastrophic optical damage threshold for these large transverse mode devices is increased by more than two times over that of conventional devices while still maintaining good device performance.