AAWSAP DIRD, Laser Lightcraft Nanosatellites, November 2010

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Average power limited by low thermal conductivity of host material.
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Wavelengths propagate extremely well in clear weather:
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Very low absorption.
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Higher scattering.
The requirements for high average power bulk solid-state lasers are [30]:
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Efficient optical pumping of gain medium:
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Flash lamp or laser diode well matched to absorption band.
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Small wavelength difference between pump and lasing ➔ low quantum defect.
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Efficient heat removal from gain medium:
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Improved heat removal techniques from host.
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Large surface area per unit volume.
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Or, large volume to store heat with low duty cycle operation.
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Gain medium must retain good (correctable) optical quality.
The typical properties of widely used Nd :YAG lasers are [30]:
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4 nm absorption line width.
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24% heating from quantum loss.
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Saturation intensity~ 3 kW/cm 2 (at~ 2% dopant).
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Multi-kilowatt average power demonstrated.
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Maximum average power potential ~several hundred kilowatts:
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Heat removal makes continuous running a challenge at this power.
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Current high-energy SSLs produce great amounts of heat (e.g., 600 kW of
electrical power in and 100 kW of beam power out equals 500 kW of waste
heat).
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Must store the waste heat and reject it from the system at a lower rate, thus
requiring storage and limited duty cycle.
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Quantum defect = pump light photon energy minus laser light photon energy.
The typical properties of widely used Yb:YAG lasers are [30]:
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18 nm absorption line width.
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Indium gallium arsenide (InGaAs) pump laser diodes at 0.941 µm wavelength:
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8.6% heating from quantum loss.
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Saturation intensity ~ 9. 7 kW/cm 2 (at ~ 25% dopant).
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Multi-kilowatt average power demonstrated.
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Maximum average power potential is perhaps 5 x Nd:YAG laser.
A new technology that enables the scaling-up of BSSSL beam power is a recently
developed thermal management system that is used to remove and store the waste
heat produced by BSSSL devices. General Atomics' Advanced Power Systems Division
recently announced* that it has completed testing of an advanced thermal energy
' Reported in Space War Newsletter, June 7, 2010.
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