R. Beach

CW and Q-switched performance of a diode end-pumped Yb:YAG laser

Using an end-pumped technology developed at LLNL we have demonstrated a Yb:YAG laser capable of delivering up to 434 W of CW power and 280 W of Q-switched power. In addition, we have frequency doubled the output to 515 nm using a dual crystal scheme to produce 76 W at 10 kHz in a 30 ns pulse length.

Compact fiber laser approach to generating 589 nm laser guide stars

We are developing an all-fiber laser system for generating 589 nm light for laser-guided adaptive optics. If only natural stars can be used to measure the turbulence in the Earths atmosphere, at most a few percent of the sky is accessible to adaptive optics correction. Laser guide stars are therefore crucial to the broad use of adaptive optics, because they facilitate access to a large fraction of possible locations on the sky. In particular, lasers tuned to the 589 nm resonance line of atomic sodium are able to create an artificial beacon at altitudes of 95-105 km, thus coming as close as possible to reproducing the light path of starlight. The deployment of multiconjugate adaptive optics on large aperture telescopes world-wide will require the use of three to five sodium laser guide stars in order to achieve uniform correction over the aperture with a high Strehl value. Current estimates place the minimum required laser power at 10 W per laser for a continuous wave source. In addition, the lasers need to be compact, efficient, robust and turnkey.

First demonstration of a diode-pumped gas (alkali vapor) laser

We report the first diode-pumped gas laser-rubidium vapor. A short cell charged with a Rb/ethane/He mixture pumped at 780 nm produced several mW in a near-confocal cavity. Issues involved in power-scaling will be discussed

Developments toward a reliable diode-pumped hydrocarbon-free 795-nm rubidium laser

We report a 795-nm diode-pumpable Rb laser using a buffer gas of pure 3He. 3He gas enhances mixing of the Rb fine-structure levels. This enables efficient lasing at reduced He pressures and improved thermal management.

Activation of a Spatial, Temporal, and Spectrally Sculpted Front End for the Mercury Laser

We have produced over 500 mJ using a hybrid fiber-based master-oscillator system coupled with a Yb:S-FAP power amplifier. This system is designed with spatial, temporal, and spectral sculpting enabling broadband amplification correctable for gain narrowing.

System operations of mercury; a diode-pumped solid-state laser

The Mercury laser project is part of a national inertial fusion energy program in which four driver technologies are being considered including solid-state lasers, krypton fluoride gas lasers, Z-Pinch and heavy ions. Mercurys operational goals of 100 J, 10 Hz, 10% efficiency in a 5 times diffraction limited spot will demonstrate the critical technologies required for scaling the system to the multi-kilojoule level. Five one hour runs were conducted to assess system stability and reliability; energy fluctuations during the 55 J operations showed a 0.6% rms deviation. Current beam quality during average power operation is approximately 10 times diffraction limited. In the future, active wavefront control, and corrector plates for steady state thermal distortions will be implemented to achieve the 5 times diffraction limited spot.

Ground State Depleted Laser Experiments

Ground state depleted (GSD) lasers have been described in an earlier paper as room temperature, four-level, high energy density lasers with uniform gain when pumped either transversely or longitudinally. Spectroscopic measurements have been performed at Livermore in various Nd doped glass and crystalline materials to extract parameters (stark resolved emission spectra, branching ratios, fluorescence lifetimes, and stimulated emission cross sections) important to the design of a GSD laser. This study has allowed us to identify several systems amenable to experimental demonstration. The results of a demonstration in one of these systems consisting of a sample of Nd doped Y2Si05 which is pumped by a flash lamp pumped dye laser will be presented. Measurements are made to document the degree to which the ground state of the laser has been depleted. An important problem present in GSD lasers, illustrated by the results of our demonstration, is holding off the gain of the Nd 4F3/2 - 4I11/2 transition which typically has an emission cross section 5 to 10 times larger than the desired 4F3/2 - 4I11/2 transition cross section. Several possible techniques for holding off the 4F3/2 - 4I 11/2 transition are discussed. These techniques include segmented laser designs, and the co-doping of laser samples with elements having a large absorption cross section in the 1.06 micron region while being relatively free of absorption in the 0.92 micron region of the spectrum. A system based on Y2SiO5 and co-doped with Nd and Sm will be presented as an example of the latter type GSD design along with available experimental results.