Laser Research and Development Studies for Laser Guide Star Systems Page: 4 of 34
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SECTION I
Introduction
The generation of sodium guide stars for adaptive optics requires very precise control of the
frequency and bandwidth of the laser to maximize the brightness of the generated guide star.
Several laser technologies have been investigated to generate visible light at the sodium D-line
for laser guide-star applications. Dye lasers can generate 589 nm light directly but are limited to
a few watts in the CW mode due to thermal issues in the dye jet, as well as the limited pump
power available. Pulsed dye lasers have been scaled to the kilowatt level with excellent beam
quality and tunable single line output. However, these lasers are complex and have high
operation and maintenance costs. There are also issues with the toxicity and flammability of the
dye mixture. The ruggedness, efficiency and ease of use of a solid state laser system has great
potential for improving the reliability and power of the laser guide star over the dye laser systems
currently used. Solid-state lasers generating 589 nm light have been demonstrated by using sum
frequency mixing in a non linear material.-8 The systems to date have had a pulsed format,
requiring very precise timing of the two independent cavities, as well as high power to generated
sufficient intensity in the nonlinear crystal external to the laser cavity. The resulting systems are
extremely complicated, high cost and easily damaged, limiting their acceptance in the adaptive
optics community. In addition, the high pump powers required for efficient external cavity sum-
frequency generation make it challenging to maintain near diffraction limited beam quality.
In this white paper we consider two CW solid state laser approaches to a 589 nm LGS system.
Both are based on the technique of sum-frequency generation, but differ in the cavity
architecture. Both technologies are very promising and are worth of further consideration. This
preliminary proposal is intended to encompass both designs. A down select shall be performed
early in the project execution to focus on the most promising option. The two design options
consist of:
1) A dual-frequency resonator with intra-cavity doubling in LBO offers the promise of a simple
architecture and may scale more easily to high power. This design has been shown to be highly
reliable, efficient and high power when used in frequency-doubled Nd:YAG lasers for programs
at LLNL and in commercial products. The challenge in this design is the demonstration of a
high power1318 rnm oscillator with adequate suppression of the 1064 nm line.
2) A MOPA based design uses commercial low power oscillators to produce both wavelengths,
then amplifies the wavelengths before doubling. This design requires the demonstration of a
1318 nm amplifier, though the design is scaled from a kW CW amplifier already delivered to a
customer at a different wavelength. The design must also demonstrate high power scaling of
sum-frequency generation in the relatively new nonlinear material, PPLN.
The first step in the process would be to further evaluate the two conceptual options for technical
feasibility, cost and constructability. Then a down selection to one design would be conducted.
Finally, R&D on that design would then proceed. Minimal testing should be required for this
selection. The majority of the funding received would be allocated to development of the design
selected.
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Pennington, D.; Beach, R.; Ebbers, C.; Erbert, G.; Nguyen, H.; Page, R. et al. Laser Research and Development Studies for Laser Guide Star Systems, report, February 23, 2000; California. (https://digital.library.unt.edu/ark:/67531/metadc742826/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.