Text of Kana Iwakuni a,b,c, Sho Okubo b,c, Hajime Inaba b,c, Kazumoto Hosaka b,c, Atsushi Onae b,c, Hiroyuki...
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Kana Iwakuni a,b,c, Sho Okubo b,c, Hajime Inaba b,c, Kazumoto Hosaka b,c, Atsushi Onae b,c, Hiroyuki Sasada a,c, Feng-Lei Hong b,c Keio University a, NMIJ, AIST b, ERATO Minoshima Intelligent Optical Synthesizer Project, JST c 69 th International Symposium on Molecular Spectroscopy, 17 June 2014, Champaign-Urbana, the University of Illinois 1 TJ03 Dual-Comb Spectroscopy of C 2 H 2, CH 4 and H 2 O over 1.0 1.7 m
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Outline 1.Optical frequency comb as a light source for spectroscopy 2.Principle of dual-comb spectroscopy 3.Observed spectra and absolute frequency measurements 2
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Optical frequency comb Fourier transformation n th mode frequency n = f ceo + n f rep : Repetition rate 0 3 T rep 1 m 2 m
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A few tens - MHz mode spacing Over 1 octave Accurate mode frequency A number of comb modes High resolution Broad bandwidth Absolute frequency measurement Rapid data acquisition 4 Application of combs - Direct frequency comb spectroscopy -
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f rep = 50 MHz 1/f rep = T rep = 20 ns f rep = 10 Hz 1/f rep = 100 ms T rep = 4 fs f rep = 50 MHz 1/f rep = T rep = 20 ns f rep = 10 Hz 1/f rep = 100 ms T rep = 4 fs Principle of dual-comb spectroscopy Detector I. Coddington et. al, PRL, 100, 013902 (2008) 5 Typical values in our experiment LO
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f rep 6 RF Principle of dual-comb spectroscopy - frequency domain - Signal comb LO comb f rep,S f rep,L f rep 2f rep f rep = f rep,S f rep,L f 2f rep f rep 0
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To observe broad spectrum f rep /2 One-to-one correspondence between signal and RF comb modes Observable spectral bandwidth 7 f rep RF f f rep /2 0 Aliasing
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To observe broad spectrum f rep /2 One-to-one correspondence between signal and RF comb modes Observable spectral bandwidth 8 f rep RF f f rep /2 0 Aliasing Observable spectral bandwidth
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To observe broad spectrum f rep /2 One-to-one correspondence between signal and RF comb modes Observable spectral bandwidth Observable spectral bandwidth 9 f rep must be small.
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To observe broad spectrum f rep /2 One-to-one correspondence between signal and RF comb modes Separate comb modes f rep < f rep Observable spectral bandwidth The relative linewidth of the two combs 10 Observable spectral bandwidth RF Relative linewidth f
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To observe broad spectrum f rep /2 One-to-one correspondence between signal and RF comb modes f rep The relative linewidth must be narrow. 11 Observable spectral bandwidth RF Relative linewidth f < f rep Observable spectral bandwidth The relative linewidth of the two combs Separate comb modes
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Fiber-based optical frequency comb EDF f rep = 48 MHz EOM /2 /4 LD 1480 nm PZT Peltier element /4 Y. Nakajima et. al, Opt. Express, 18, 1667 (2010) K. Iwakuni et. al, Opt. Express, 20, 13769 (2012) Average power: a few mW 0.5 MHz 12 Delay line output
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13 RBW: 1Hz VBW: 1Hz Less than 1 Hz 5 Hz Measurement of the relative linewidth Signal / arb. unit (linear scale) Relative frequency / Hz
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Experimental setup CW 1535 nm RF 30 MHz Signal comb LO comb f ceo detector f rep,LO = 48.000 000 MHz f rep,S = 48.000 007 MHz Bandwidth 100 MHz Spectrum Bandwidth 1.0-1.7 m White cell Digitizer LPF f rep 7 Hz /2 PBS 14 Reference signals 12 C 2 H 2, 20 Torr
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Observed interferogram f rep = 9 Hz Minimum acquisition time to observe whole spectrum: 110 ms Average: 50,000 times Total measurement time: 90 min Free Induction Decay (FID) 12 C 2 H 2, 20 Torr, White cell (15cm, 13 round trips ) Time / ns 0 2040 - 20 - 40 Time / ns 0 2 4 68 10 Time / ns 0.360.37 0.38 0.39 0.4 1 / 2B
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16 Observed spectrum f rep = 7 Hz Minimum acquisition time to observe whole spectrum : 140 ms Average: 400, 000 times Total measurement time: 16 h 12 C 2 H 2, 20 Torr, White cell (15cm, 13 round trips ) CH 4, 20 Torr, Cell (50cm) 6,000 8,000 10,000 Wavenumber (cm -1 ) 180 200 220 240 260 280 300 Frequency (THz) CH 4, 20 Torr White cell 50 cm 12 C 2 H 2, 20 Torr 15 cm, 13 round trips Detector LO
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17 Observed spectrum f rep = 7 Hz Minimum acquisition time to observe whole spectrum : 140 ms Average: 400, 000 times Total measurement time: 16 h 12 C 2 H 2, 20 Torr, White cell (15cm, 13 round trips ) CH 4, 20 Torr, Cell (50cm) 6,000 8,000 10,000 Wavenumber (cm -1 ) 180 200 220 240 260 280 300 Frequency (THz) Transmitted power (arb. unit) 10 1 0.1 0.01
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180 200 220 240 260 280 300 18 Frequency (THz) 176 178 180 182 184 Transmitted power (arb. unit) 40 30 20 10 Observed spectrum 12 C 2 H 2, 20 Torr, White cell (15cm, 13 round trips ) CH 4, 20 Torr, Cell (50cm) 0 CH 4, 2 3 1.67 m 6,000 8,000 10,000 Wavenumber (cm -1 ) Transmitted power (arb. unit) 10 1 0.1 0.01
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180 200 220 240 260 280 300 19 30 20 10 0 Frequency (THz) 194 196 198 200 Observed spectrum 12 C 2 H 2, 20 Torr, White cell (15cm, 13 round trips ) CH 4, 20 Torr, Cell (50cm) 12 C 2 H 2, 1 3 Transmitted power (arb. unit) 1.53 m 6,000 8,000 10,000 Wavenumber (cm -1 ) Transmitted power (arb. unit) 10 1 0.1 0.01
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180 200 220 240 260 280 300 20 6 4 2 0 8 10 200 205 210 215 220 225 Frequency (THz) Observed spectrum 12 C 2 H 2, 20 Torr, White cell (15cm, 13 round trips ) CH 4, 20 Torr, Cell (50cm) Transmitted power (arb. unit) 1.46 m H 2 O, 2 2 + 3 6,000 8,000 10,000 Wavenumber (cm -1 ) Transmitted power (arb. unit) 10 1 0.1 0.01
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180 200 220 240 260 280 300 21 Transmitted power (arb. unit) 10 1 0.1 0.01 Observed spectrum 12 C 2 H 2, 20 Torr, White cell (15cm, 13 round trips ) CH 4, 20 Torr, Cell (50cm) 3 2 1 4 5 286 287 288 289 290 291 292 Frequency (THz) 0 Transmitted power (arb. unit) 12 C 2 H 2, 2 1 + 3 1.03 m 6,000 8,000 10,000 Wavenumber (cm -1 )
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22 Transmitted power (arb. unit) Observed spectrum 12 C 2 H 2, 20 Torr, White cell (15cm, 13 round trips ) CH 4, 20 Torr, Cell (50cm) 12 C 2 H 2 1.46 m H2OH2O 12 C 2 H 2 1.53 m 1.03 m CH 4 1.67 m Wavenumber (cm -1 ) 6,000 8,000 10,000 Transmitted power (arb. unit) 10 1 0.1 0.01
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Sensitivity 23 10 times avg. (Measurement time: 1 s) 100 times avg. (Measurement time: 10 s) 1000 times avg. (Measurement time: 100 s) S/N 5S/N 11S/N 38 (without fringes) S/N 15 (with fringes) 1 + 3 vibration band 12 C 2 H 2, 20 Torr, White cell (15cm, 13 round trips ) f rep = 9 Hz Minimum acquisition time to observe whole spectrum: 110 ms Limited by background fringes
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Absolute frequency measurement 24 ( 194 742 519. 0 2.6 ) MHz P(23) Frequency / THz Transmitted signal ( 194 742 536. 722 9 0.0018 ) MHz Determined frequency from the fitting Previous work (sub-Doppler resolution) The discrepancy comes from the pressure shift and the residual fringes. A. Madej et. al, JOSA B, 23, 2200 (2006) 12 C 2 H 2, 20 Torr, White cell (15cm, 13 round trips ) f rep = 9 Hz Minimum acquisition time to observe whole spectrum: 110 ms Average: 50,000 times Total measurement time: 90 min 1313 194 195 196 197 198 Frequency / THz 6500 6550 6600 Wavenumber / cm -1 Transmitted signal Phase / rad
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Summary Acknowledgments We are grateful to Dr. K. M. T. Yamada for his helps to this research. This research is financially supported by Grand-in-Aid for Scientific Research (A) of the Ministry of Education, Culture, Sports, Science and Technology, Japan. 25 We developed the dual-comb spectrometer using two combs with narrow relative linewidth, and simultaneously observed absorption spectrum of 12 C 2 H 2, CH 4 and H 2 O over 1.0 - 1.7 m in 140 ms. The sensitivity is currently limited by the residual fringes.
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Scale the horizontal axis f RF opt Signal LO 26
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0 10 20 30 40 50 Lab. time / ms 0 25 50 75 100 125 Effective time / ns 51.05 51.0525 51.055 51.0575 effective time / ns lab. time / ms 22.462 22.463 22.464 22.465 Observed five interferograms f rep = 95 Hz 1 shot measurement time: 53 ms Average: 30 times Total measurement time: 1.6 s 27
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Separation of comb modes R (12) R (13) 1 + 3 192 194 196 198 200 202 Absolute frequency / THz f rep,S R (12) 500 MHz 13 C 2 H 2 28
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f ceo CW laser #1 Function generator 30 MHz Pump LD f beat 29 Signal comb LO comb Pump LD EOM, PZT, Peltier CW laser #2 RBW: 1Hz VBW: 1Hz Less than 1 Hz 5 Hz PZT Temp. Measurement of the relative linewidth
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700 kHz In-loop beat signal 4 MHz RBW : 30 kHz VBW : 10 kHz f ceo f beat 30
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Application of combs Frequency counter f beat laser Sample gas 31
