nd:yag laser power cycling the direct detection doppler lidar uses a frequency tripled nd:yag laser,...
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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 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
10 156W 142W 315 million
30 303.4W 276W 945 million
50 451W 410W 1.58 billion
70 600W 546W 2.20
100 820W 750W 3.15 billion
Laser Power Cycling Backups
D. Barry Coyle 554/601 [email protected]
HOMER Diode Arrays’ Long Term Performance
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)
FIBERTEK, INC. Raytheon 1 J Risk Reduction Laser Optical Layout
Final System Optical Configuration
Both the original NASA Ozone amplifiers and the power amplifier have been shown to be capable of 100 Hz operation
Power amplifier
Expansiontelescope
Amplifier #2
Amplifier #1
LBO doubler
355 nm output
LBO tripler
Fiber port
Ring Resonator
Fiber-coupled 1 m seed laser
Optical isolator
FIBERTEK, INC. Raytheon Laser Transmitter Alternate Duty Cycle Operation
Measured 1064 nm output during typical Off/On cycle
“Off” operation is in Armed mode (87 W)
“On” operation in HPWR mode (687 W)
88% of full power is reached in 1.5 minutes
93% of full power is reached in 2 minutes
10% duty cycle - 147 W average power - 687 W peak power
50% duty cycle - 387 W average power - 687 W peak power
100% duty cycle - 687 W average power - 687 W peak power
1064 nm power vs. time after Armed to High Power transition
Time (minutes)
0 2 4 6
1064 nm output power (W)
0
10
20
30
40
50
FIBERTEK, INC.
COLD1
WARMUP2
FAULT3
HPWR6
LPWR5
DIAG7
ARMED4
Power-up WARMUPFAULTARMEDLPWRHPWRDIAG
ARMEDLPWRHPWRDIAG
LPWRHPWRDIAG
CNTRL INITIALIZE
CNTRL LASERDISARMCNTRL HTRSON
CNTRL CLRINT
CNTRL LASERARM CNTRL LPWRMODE
CNTRL HPWRMODE
CNTRL DIAGMODE
CNTRL LPWRMODE
CNTRL HPWRMODE
CNTRL STOP
WARMUPARMEDLPWRHPWRDIAG
Any activefault
“1”
“4”
“-” (hyphen)
“D”
“7”
“2”
“8”
“C”
“C”
“A”
“A”
Blue text indicates alternative command characters when operating laser system from Hyperterminal serial interface
Raytheon Laser TransmitterModes and Power Consumption
28 W
32 W
687 W
687 W
687 W
87 W
FIBERTEK, INC.
COLD:Control electronics onHeaters offFaults suppressedDiode power supplies offAll diode & QS pulses off
WARMUP:THG and SHG heaters onFaults acknowledgedDiode power supplies offAll diode & QS pulses off
FAULT:Active fault detected/latchedHeaters on (unless heater fault is active)Diode power supplies offAll diode & QS pulses off
ARMED:THG and SHG heaters onTHG and SHG at nominal temperaturesFaults acknowledgedSeed laser onDiode power supplies onAll diode & QS pulses off
HPWR:Heaters onFaults acknowledgedDiode power supplies onAll diode pulses on, nominal PWQS onFull optical output power (after ramp-up)
LPWR:Heaters onFaults acknowledgedDiode power supplies onAll diode pulses on, nominal PWQS onLow optical output power
DIAG:Heaters onFaults acknowledgedDiode power supplies onAll diode pulses onQS offNo significant optical output
Raytheon Laser TransmitterState Definitions
FIBERTEK, INC. Raytheon Laser Transmitter Measured System Performance
Current system, 100% duty cycle, 50 Hz operation
Total DC power consumption (nominal 28 V) at 45.6 W (912 mJ/pulse @ 50 Hz) 1064 nm
output was 687 W (27.7 V, 24.8 A)
6.6% system level wall plug efficiency @ 1064 nm
Laser mass - 43 kg
Laser volume - 10 cm x 42 cm x 69 cm = 29,000 cm3
Preliminary 355 nm results - 300 mJ @ 50 Hz
2.2% system level wall plug efficiency @ 355 nm
Expected 355 nm results - >410 mJ @ 50 Hz (>45% THG)
>3% system level wall plug efficiency @ 355 nm