Nd:YAG Laser Power Cycling. The Direct Detection Doppler Lidar uses a frequency tripled Nd:YAG laser, the same laser technology used in MOLA, GLAS, MLA, CALIPSO. Significantly higher pulse energy/ average power is required for the Doppler measurement. - PowerPoint PPT Presentation
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Nd:YAG Laser Power Cycling • The Direct Detection Doppler Lidar uses a frequency tripled Nd:YAG laser, the same laser technology used in MOLA, GLAS, MLA, CALIPSO. Significantly higher pulse energy/ average power is required for the Doppler measurement. • GWOS DD laser has nominal pulse energy of 360 mJ @ 355 nm at a repetition frequency of 100 pps 36W optical power. • Assuming 4.4% wall plug efficiency to 355 nm the electrical power draw is about 820W. • Since only about 9% of the electrical power is converted to photons the remaining power (750W) will need to be dissipated by the thermal system. • 3.15 billion shots/year. • Question: What are the benefits of operating the laser at a lower duty cycle on a per orbit
Transcript
Nd:YAG Laser Power Cycling
• The Direct Detection Doppler Lidar uses a frequency tripled Nd:YAG laser, the same laser technology used in MOLA, GLAS, MLA, CALIPSO. Significantly higher pulse energy/ average power is required for the Doppler measurement.• GWOS DD laser has nominal pulse energy of 360 mJ @ 355 nm at a repetition frequency of 100 pps 36W optical power.
• Assuming 4.4% wall plug efficiency to 355 nm the electrical power draw is about 820W. • Since only about 9% of the electrical power is converted to photons the remaining power (750W) will need to be dissipated by the thermal system.• 3.15 billion shots/year.
• Question: What are the benefits of operating the laser at a lower duty cycle on a per orbit basis? 10%< duty cycle < 100%.
• Laser lifetime improves – Operation at a duty cycle of N% reduces the shot count
proportionally – Recent testing of 808 nm pump diodes at 30% duty cycle shows
little or no degradation of the output. Tests are up to 6B shots
• Supposition: If power is cycled on every orbit, the orbit averaged electrical power can be reduced by some fraction. – When not acquiring science data we will assume 10% of total
average power is required to maintain the laser in standby mode.– For duty cycle N, the orbit averaged power = (N*Total power)+ (1-
N)*0.1*Total Power– Orbit averaged thermal load is also reduced.
AverageThermal=0.91*AveragePower. Note – to take advantage of this the thermal system must be able to operate with variable heat load to avoid significant over-cooling of the laser when in standby mode.
Potential Savings from Laser Power Cycling
GWOS DD Laser Power Cycling
Duty cycle (%) Orbit Avg Power Thermal load Shots/year
Two sets of HOMER LDA’s installed on in-house lifetest station, operated at HOMER’s 17 mJ pulse energy specs @ 242 Hz.
• Set A: (top) Power Cycled Operation- 4 G4’s, 25C, 50A, 80us- > 5.74 B shots - > 21900 cycles- no measureable decay (within 2% cumulative instrument noise)
• Set B: (top) Continuous Operation- 4 G4’s, 25C, 50A, 80us- > 6.43 B shots- no measureable decay (within 2% cumulative instrument noise)
Early Conclusions: 1. Extensive in-house screening procedures are proving accurate and repeatable.2. Proper derating insures long life: >> 10B shots3. Power cycling high power QCW arrays does NOT reduce liftime, under these conditions.
Research jointly funded by Biomass Monitoring Mission (BioMM) and Laser risk reduction program (LRRP)
