George F. Albrecht

High average powers diode pumped slab laser

The authors have developed and tested stackable microchannel cooled laser bar diode pump packages suitable for direct pumping of slab lasers at high duty factor. A stack of 41 diode packages gives a pump array of 13.5 cm/sup 2/ and produces a peak power of 4000 W and an average power of 1000 W for an average irradiance of 75 W/cm/sup 2/. A high average power, total internal reflection face pumped Nd:YAG laser using 80 diode packages has been constructed. Preliminary testing of the slab laser using a 20% subset of diode packages arranged to pump a 4 mm*4 mm*80 mm volume of the slab has been completed. Seventy watts average power is obtained at 2.5 kHz pulse repetition rates and 100 mu s pulse widths. >

Characterization of the heat loading of Nd-doped YAG, YOS, YLF, and GGG excited at diode pumping wavelengths

The parameter /spl xi/ (xi) is proposed as an alternative to the traditional solid-state laser media heating parameter, /spl chi/ (chi). /spl xi/ is the ratio of heat produced to energy absorbed, and /spl chi/ is the ratio of heat produced to the maximum stored energy in the upper laser level. The parameter /spl xi/ is particularly relevant to diode pumped systems. We demonstrate an experimental /spl xi/ characterization based on the determination of the steady state cooling rate (hence heating rate) of small sample crystals subjected to pump laser heating. Using measured fluorescent lifetimes of the samples and near zero doping (intrinsic) values, the doping independent (zero doping or zero quenching) parameters /spl chi//spl phi/ and /spl xi//spl phi/ are determined. The results for all samples are in excellent agreement with calculations based solely on energy defect and nonradiative quenching of the upper level. >

Solid state heat capacity disk laser

This paper describes a solid state laser concept that scales to MW levels of burst power and MJ of burst energy and burst durations measured in seconds. During lasing action, waste heat is purposely stored in the heat capacity of the active medium. The paper outlines the principal scaling laws of key operational features and arrives at a conceptual design example of the laser head as well as a mobile laser system.

24-W average power at 0.537 μm from an externally frequency-doubled Q-switched diode-pumped Nd:YOS laser oscillator

A diode-pumped single Nd:YOS rod laser is operated at 110 Hz with 830-mJ free-lase pulses and 380-mJ, 13-ns (FWHM) Q-switched pulses. External doubling with an 8-mm-long KTP crystal results in 24 W at 0.537 µm after thermalization.

Simple analytical method to calculate the radial energy deposition profile in an isotropic diode-pumped solid-state laser rod

We provide an approximate but simple analytical solution to the radial distribution of deposited energy in a diode-array-pumped laser rod, subject to some assumptions that are naturally fulfilled for most applications of practical interest. The solution is useful to survey quickly irradiance distributions for a wide variety of pumping geometries and to find the radially most uniform energy deposition. We find that the radial deposition profile, as well as the pump light absorption efficiency, is largely controlled by just two dimensionless parameters: the number of absorption depths and the ratio of the width of the unabsorbed pump beam at the rod center divided by the rod radius. A side-by-side comparison with a numerical model is given. Results describing the best achievable trade-off between absorption efficiency and pumping uniformity are presented in the form of a recipe that can be followed without studying our research in detail. Finally, the model equations are applied to a practical side-pumped geometry.

One-kilowatt average-power diode-pumped Nd:YAG folded zigzag slab laser

High average power Nd:YAG lasers are increasingly interesting for industrial applications such as drilling and machining. Diode pumping of this solid state medium offers longer services intervals, reduced thermal optical distortions, higher system efficiency and more compact packaging than lamp pumping. The zigzag slab geometry is well suited for applications where the average power exceeds a few hundred watts and a good beam quality is desired, particularly if the laser pumping level is to be varied. We present the status of our latest upgrade to our (originally 300 watt1) diode pumped slab laser. In what follows we first describe the diode pump source. We then discuss the zigzag slab laser design and its present performance.

100 W average power at 0.53 μm by external frequency conversion of an electro‐optically Q‐switched diode‐pumped power oscillator

We have generated approximately 100 W of frequency doubled light from the output of an electro‐optically Q‐switched diode‐pumped Nd:YAG slab laser oscillator operating at an average power of 200 W (2.5 kHz repetition rate, 80 mJ/pulse, 30 ns pulsewidth). The Q‐switch was a compensated z‐axis propagation LiNbO3 electro‐optic modulator, and the frequency conversion crystal was a thin slab of KTP. In addition, Q‐switched operation at an average power of approximately 250 W with 26 ns pulsewidths has been demonstrated.

Flash-lamp-pumped laser operation of Nd 3+ :Y 2 SiO 5 at 1.074 μm

Flash-lamp-pumped laser operation of Nd3+:Y2SiO5 by use of the Nd3+ 4F3/2−4F11/2 transition at 1.074 μm is obtained and compared with that from an identically pumped standard-doped Nd3+:YAG rod. Higher free-laser performance in Nd3+:Y2SiO5 is attributed to its higher doping. Approximately 2.5 times more energy in Q-switched pulses is generated in the Nd3+:Y2SiO5 rod than in the prelase-limited Nd:YAG rod.

Q-switched laser at 912 nm using ground-state-depleted neodymium in yttrium orthosilicate.

A ground-state-depleted laser is demonstrated in the form of a Q-switched oscillator operating at 912 nm. By using Nd(3+) as the active ion and Y(2)SiO(5) as the host material, the laser transition is from the lowest-lying Stark level of the Nd(3+4)F(?) level to a Stark level 355 cm(-1) above the lowest-lying one in the (4)I(9/2) manifold. The necessity of depleting the ground (4)I(9/2) manifold is evident for this level scheme as transparency requires a 10% inversion. To achieve the high excitation levels required for the efficient operation of this laser, bleach-wave pumping using an alexandrite laser at 745 nm has been employed. With KNbO(3), noncritical phase matching is possible at 140 degrees C using d(32) and is demonstrated.

Thermal management in inertial fusion energy slab amplifiers

As the technology associated with the development of solid-state drivers for inertial fusion energy (IFE) has evolved, increased emphasis has been placed on the development of an efficient approach for managing the waste heat generated in the laser media. This paper addresses the technical issues associated with the gas cooling of large aperture slabs, where the laser beam propagates through the cooling fluid. It is shown that the major consequence of proper thermal management is the introduction of simple wedge, or beam steering, into the system. Achieving proper thermal management requires careful consideration of the geometry, cooling fluid characteristics, cooling flow characteristics, as well as the thermal/mechanical/optical characteristics of the laser media. Particularly important are the effects of cooling rate variation and turbulent scattering on the system optical performance. Helium is shown to have an overwhelming advantage with respect to turbulent scattering losses. To mitigate cooling rate variations, we introduce the concept of flow conditioning. Finally, optical path length variations across the aperture are calculated. A comparison of two laser materials (S-FAP and YAG) shows the benefit of a nearly a-thermal material on optical variations in the system.