Lecture 17. Temperature Lidar (6) Na Resonance-Doppler Lidar Instrumentation

Transcription

1 Lecture 17. Temperature Lidar (6) Na Resonance-Doppler Lidar Instrumentation q Introduction: Requirements for Na Doppler Lidar q Classic Na Doppler Lidar Instrumentation Ø Na Doppler Lidar System Ø Key Technologies in Classic Na Doppler Lidar Ø High-Efficiency Lidar Receivers Ø Narrowband Filters for Daytime Measurements q More Options for Na Doppler Lidar Instrumentation q Summary 1

2 Introduction Interaction between radiation and objects Radiation Propagation Through Medium Transmitter (Radiation Source) Signal Propagation Through Medium Receiver (Light Collection & Detection) Data Acquisition & Control System Data Processing, Analysis & Interpretation q Resonance Doppler lidar has the frequency discriminator in atmosphere - atomic absorption lines! ð Narrowband transmitter, broadband receiver. ð High signal levels and accurate knowledge on the frequency discriminator! 2

3 Recall 3-Frequency Ratio Doppler Tech Effective Cross Section (m 2 ) 1.2 x f - f a f K 200 K 250 K Effective Cross Section (m 2 ) Frequency Offset (Hz) x x f - f a f + 50 m/s 0 m/s +50 m/s Frequency Offset (Hz) x

4 Recall Calibration Curves for 3-Freq q R T is sensitive to temperature, while R W is sensitive to wind. q For given temperatures and winds, we can compute the Doppler lidar calibration curves from atomic physics and lidar physics. -40 m/s Isoline / Isogram 180 K 4

5 Requirements for Na Doppler Lidar q To infer Doppler broadening and shift with sufficient accuracy & precision, the lidar transmitter must provide narrowband laser light at three (at least) independent frequencies that are sensitive to temperature and LOS wind. σ e = σ D 2 + σ L 2 This is because the return Na fluorescence signal s intensity lineshape is a convolution of Na absorption coefficient lineshape with laser lineshape. Ø If σ L σ D, the fluctuation of σ L will dominate the temp errors. Ø If σ L ~σ D /10, σ D dominates the convolution linewidth but laser lineshape still affects the results. So it s important to know laser lineshape well. Ø If σ L ~σ D /100, the convolution linewidth is basically determined by σ D and the laser lineshape doesn t affect the results anymore (minimal). q For temperature measurements, stable and repeatable frequencies must be achieved for all three frequencies. q An extra and critical requirement for wind measurements is to achieve accurate frequencies, i.e., well-calibrated absolute frequencies. 5

6 Classic Na Doppler Lidar Dye-laser-based Na wind and temperature Doppler Lidar (See details in our textbook Chapter 5) 6

7 Na Lidar Transmitter Photo 1 AOM Na Vapor Cell Verdi Laser Wavemeter Ring Dye Laser 7

8 Na Lidar Transmitter Photo 2 Ring Dye Laser PDA Nd:YAG 8

9 Na Wind and Temperature Lidar Na Wind/Temperature Lidar Diagram Receiving Telescope P1 B P2 HV Power Supply Cathode PMT Chiller Power Supply Power Supply Mirror Outgoing Beam 1.5-2W@50pps 589nm Shutter λ/4 Shutter Drive Trigger IN Optical Fiber CH1 Collimation Lens Pulsed Dye Amplifier Trigger IN Crystal Oscillator 315MHz AO Driver CH2 Trigger IN Na Cell Faraday Filter AO Shifter AO Shifter + _ λ/2 Isolator Temperature Control Sensor Interference Filter 17.5W@50pps 532nm Na Vapor Cell PD P.B.S. Heater Current Pre-Amplifier (Optical Power Meter) PMT PMT Housing And Chiller Q-Switch Sync. Collimator Pre-Amplifier Osci. Sync. Frequency Doubled Pulsed Nd:YAG Laser Chopper Anode Neutral Density Filter CW Nd:YVO4 Verdi Laser B.S. 5mW@ 1064nm 532 nm 4-5 W Discriminator Injection Seeder CW YAG Laser λ/2 Wavemeter CW Ring Dye Laser 589nm W Signal In Scaler 3 SRS430 (10) Signal Divider Scaler 2 In SRS430 (9) Signal In Scaler 1 SRS430 (8) Data Computer GPIB GPIB A/D Trigger In Trigger In Trigger In Trigger In Frequency Divider (/50) Shifter Trigger In States Shifter Computer Control Bit In EXT TRIG IN AO - Delay DG535 Selector AO + + T0 Delayed Trigger In Shutter Amplifier Verdi Laser Power Supply Ring Laser Control EXT SCAN X Y Oscilloscope LPFilter I/O Box A/D Shutter 9

10 Na Doppler Lidar Transmitter Pulsed 589 nm W Pulsed Dye Amplifier 532 nm 16.5 W Pulsed Frequency-Doubled Nd:YAG Laser 1064 nm 5 mw CW Injection Seeder Laser Optical Isolator Acoustic-Optic Frequency Shifter ± 630 MHz Na Vapor Cell Wavemeter Photo Detector CW Frequency-Doubled Nd:YVO 4 Laser 532 nm 4 W CW Ring Dye Laser 589 nm W 10

11 Steerable Na Doppler Lidar [Chu et al., JGR, 2005] Large-Aperture (3.5m) Steerable Na Doppler Lidar Led by Professor Chester S. Gardner of UIUC 11

12 LIDAR REMOTE SENSING PROF. XINZHAO CHU CU-BOULDER, SPRING 2016 Large-Aperture Na Doppler Lidar 12

13 Key Technologies in Classic Na Doppler Lidar 1. How to achieve single-frequency CW laser source? -- Ring Dye Laser (RDL) with sophisticated design 2. How to lock the CW laser frequency to well-calibrated reference? -- Phase-sensitive detection and servo loop for freq. locking 3. How to achieve an absolute frequency reference? -- Na vapor cell and Doppler-free saturation-absorption spectroscopy 4. How to achieve wing frequencies after achieving the peak freq? -- Acousto-Optic Modulators (AOMs), dual channel, double-pass 5. How to amplify the CW laser to generate quasi-pulsed laser? -- Pulsed Dye Amplifier (PDA) pumped by injection-seeded Nd:YAG laser 6. How to compress background to enable daytime measurements? -- Faraday filter or Fabry-Perot etalon with narrowband interference filter 13

14 Ring Dye Laser: Single-Frequency ICA 589nm 532nm Brewster Plate From Verdi 1. Four mirror + Dye jet form the laser resonance cavity. 2. Unidirectional lasing prevents spatial hole-burning. 3. Rhomb compensates the astigmatism effect. 4. Optical diode forces the unidirectional lasing. 5. BRF + ICA (etalons) select frequency and narrow bandwidth. 6. Brewster plate + RCA + M3 PZT actively control frequency. 14

15 Frequency Selection in Ring Laser (FWHM=200 GHz) (FWHM=2 THz) (FWHM=5 GHz) 15

16 Master Oscillator and Freq Locking with Doppler- Free Spectroscopy [Smith et al., OE, 2009] See detailed explanations on Na Doppler-free saturation-fluorescence spectroscopy in Textbook Chapter

17 Doppler-Free Na Spectroscopy f - f a f + See detailed explanation on Na Doppler-free saturation-fluorescence spectroscopy in Textbook Chapter e a ν a ν c ν b ν c =(ν a +ν b )/2 b 17

18 Excited State LIDAR REMOTE SENSING PROF. XINZHAO CHU CU-BOULDER, SPRING 2016 Doppler-Free Spectroscopy: Ground-state Cross-over vs. Excited-state Cross-over 4 3 #(,# #(+' #(+#!"#$%&'$%()*"+,-)'.%()*"#./0%'&1"$%"2-3 Ground State 2 1 4*%/*-(%5"6$7"&78 - #(*' #(*# #()' #()# #(''!"##!$##!%##!&## # &## %## $## "## '## 9'/:&/*05";<<-/%"6=>? %(8*#,/*#&9"(:;%9/<#&9"(8<$1#/,=(*#(>,?* ( 7%(8*#,/*#&9"(:;%9/<#&9"(8<$1#/,=(*#(> )?; ( #'" ('# #'+ #'$ #'&!"#$"%&#'()*+(,+-, #'* #'% #') #'& #'(,!"#$"%&#'()*+(,+- ) #'" #'$ #'% ) #'#!"##!$##!%##!&## # &## %##./$0,$"1'(233%$#()456-, [Chu et al., ILRC, 2008] #'#!"##!$##!%## # %## $## "## &##./$0,$"1'(233%$#()456- ) 18

19 Hardware LIDAR REMOTE SENSING PROF. XINZHAO CHU CU-BOULDER, SPRING 2016 Acousto-Optic Modulator (AOM) Mirror λ/4 Waveplate Shutter Shutter Drive L 3 AO Shifter + CH1 L 2 Crystal Oscillator 315MHz AO Driver AO Shifter _ CH2 To PDA L 1 λ/2 Waveplate Optical Isolator Polarized Beam Splitter Ring Laser Light Explanation: Doppler shift or Photon/Phonon Annihilation Diffracted Beam Ultrasonic Transducer θ Electric Input λs AO Crystal θ Sound wave fronts Incident Beam Diffracted Beam Ultrasonic Transducer θ λs Sound wave fronts Electric Input AO Crystal θ Incident Beam (b) (a) 19

20 Pulsed Amplification: PDA Fast Photo-Diode Linear Phase Amplifier Digitizer Computer λ/2 cw PBS AOM Mirror ND Filter Optical Isolator λ/2 Injection-Seeded Frequency-Doubled Nd:YAG Laser CL1 CL2 PDA DC1 DC2 DC3 1. Amplified Spontaneous Emission (ASE) 2. Injection-seeded Nd:YAG laser 3. PDA chirp caused by pulsed amplification 20

21 Na Doppler Lidar Control System and Data Acquisition Recent improvements: 1) Seed laser frequency locking: phase-sensitive 2) Computer-card based multichannel scalers 3) High-QE PMTs (issues with max count rate) 4) Primary-focus larger aperture telescope 5) LabVIEW-based DAQ 6) Daytime capability 21

22 STAR Na LIDAR Modernized DAQ, System Control, and Receiver Receiver PMT Discriminated PMT Signal PC Data Acquisition & Control < Mirror Control (RS -485) > < Camera Control (USB) > Newtonian > Q-Switch Trigger > TTL B N C > Locking Feedback > Analog/Digital/Counter Channel Connections Transmitter SHG 532 nm 1064 nm Frequency-Doubled Nd:YAG Pulsed, Q-Switched Laser Shutter Driver Oscilloscope Doppler Free Spectroscopy AOM Driver Photodiode Hot Na Vapor Cell ND Filter SM Fiber Wavemeter λ/2 λ/4 Shutter 20 cm AOM 10 cm AOM 20 cm Acousto-Optic Modulation Periscope Pulsed Dye Amplifier λ/2 To Sky CMOS Optical isolator Master Oscillator CW 532 nm Pump Laser Collimator Single-Mode Ring Dye Laser Iris Ring Dye Laser Control Box Actuated Steering Mirror [J. A. Smith, W. Fong, X. Chu, et al., University of Colorado] 22

23 LIDAR REMOTE SENSING PROF. XINZHAO CHU CU-BOULDER, SPRING 2016 STAR Na Doppler Lidar Receiver MM fiber CU-Boulder STAR Na Doppler Lidar Primary Focus Telescope Fiber Coupling Chopper PMT Prime-focus telescope s primary mirror ê Multimode Optical Fiber Receiver Chain 23

24 High-Efficiency Lidar Receiver Dr. John Smith s Excellent PhD Research [Smith and Chu, AO, 2015] AO_SmithChu_HighEfficiencyLidarArchitecture.pdf 24

25 STAR Na Doppler Lidar DAQ Shots/Freq Chopper PMT Multimode Optical Fiber Receiver Chain 25

26 High-Efficiency Lidar Leading to New Science Inquiries Chopper PMT Multimode Optical Fiber [Smith and Chu, Applied Optics, 2015] Receiver Chain 26

27 Narrowband Daytime Filter: Faraday Filter for Na Doppler Lidar Set up of Na Faraday Filter eiving scope P 1 B P 2 Na Cell HV Power Supply Cathode PMT A Collimation Lens Transmission Faraday Filter Interference Filter See textbook Chapter 5 f 0 PMT Housing And Chiller PMT Receiver Chain Frequency 27

28 STAR Na Doppler LIDAR Transmitter Transmitter Doppler Free Spectroscopy SHG Frequency-Doubled Nd:YAG Pulsed, Q-Switched Laser Oscilloscope Photodiode Hot Na Vapor Cell ND Filter 532 nm 1064 nm Shutter Driver AOM Driver SM Fiber Wavemeter λ/2 λ/4 Shutter 20 cm AOM 10 cm AOM 20 cm Acousto-Optic Modulation Periscope Pulsed Dye Amplifier λ/2 To Sky CMOS Optical isolator Master Oscillator CW 532 nm Pump Laser Collimator Single-Mode Ring Dye Laser Iris Ring Dye Laser Control Box Actuated Steering Mirror 28

29 Options for Na Doppler Lidar q Conventional: Ring Dye Laser + PDA q Hybrid: Solid-state cw 589nm source + PDA -- CW Nd:YAG lasers SFG (1064 and > 589 nm) -- CW fiber lasers SFG (1583 and 938 -> 589 nm) -- Raman shifted fiber laser SHG (1178->589 nm) -- ECDL/DFB + Fiber Amplifier + SHG (1178->589 nm) Toptica q Full solid-state pulsed 589nm laser -- Flashlamp pumped Nd:YAG lasers SFG -- Diode-laser pumped Nd:YAG laser SFG -- Self-Raman Nd:YVO 4 pulsed laser: 1064->1178->589 nm q Solid-state cw 589nm laser + pseudorandom modulation or cw 589nm laser + bistatic configuration 29

30 Solid-State Na Doppler Lidar q Japanese Shinshu system by Kawahara et al.: Frequency mixing of two Nd:YAG lasers at 1064 and 1319 nm 30

31 Solid-State Na Doppler Lidar Based on Diode-Laser- Pumped Nd:YAG Lasers [Kawahara et al., ILRC, 2008] 31

32 Summary q A state-of-the-art Na Doppler lidar is the dye-laser-based Na wind and temperature lidar -- ring dye laser + pulsed dye amplifier configuration. STAR Na Doppler lidar is a modern version of it. q A main feature is the narrowband Na lidar transmitter with accurate and precise frequency control and narrowband laser: Na Doppler-free spectroscopy for frequency calibration and locking, acousto-optic frequency modulator for generating two wing frequencies with high stability and fast switching, pulsed amplification with very low ASE. q The lidar receiver (broadband) and DAQ subsystems have various styles and forms. They are also progressing rapidly. High-efficiency lidar receiver design enables the very high-resolution lidar measurements for new science endeavors. q Daytime filters based on Faraday filter enable full diurnal cycle measurements, which makes the Na Doppler lidar a golden standard. q Na Doppler lidar can be realized with many other laser configurations, and its technologies will continue evolving with advancement of laser, electronics, fiber optics, detector, data acquisition, etc. technologies. 32