Optical Frequency Comb Fourier Transform Spectroscopy with Resolution beyond the Path Difference Limit

Transcription

1 Optical Frequency Comb Fourier Transform Spectroscopy with Resolution beyond the Path Difference Limit Aleksandra Foltynowicz, Alexandra C. Johansson, Amir Khodabakhsh, Lucile Rutkowski Department of Physics, Umeå University, Sweden Piotr Masłowski, Grzegorz Kowzan Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Torun, Poland Kevin F. Lee and Martin E. Fermann IMRA America, Inc, Ann Arbor, MI, USA CES2015, Boulder, CO, June 2015

2 Introduction FTIR widely used technique Spectroscopy Physics Chemistry Material science Biology Challenges of high-resolution measurement Large instrument (optical path difference, OPD) Long measurement time Vacuum and temperature stabilization Distortion by instrumental lineshape function (ILS) Our method ILS-free spectra with absorption lines narrower than the nominal resolution Optical frequency comb as a light source OPD equal to c/f rep Small instrument, short acquisition times

3 Introduction FTIR widely used technique Spectroscopy Physics Chemistry Material science Biology Challenges of high-resolution measurement Large instrument (optical path difference, OPD) Long measurement time Vacuum and temperature stabilization Distortion by instrumental lineshape function (ILS) Our method ILS-free spectra with absorption lines narrower than the nominal resolution Optical frequency comb as a light source OPD equal to c/f rep Small instrument, short acquisition times

4 FTIR Resolution Fourier transform spectrometer Michelson interferometer Nominal resolution Inverse of the maximum optical path difference 1 δν N = OPD max

5 FTIR Resolution Fourier transform spectrometer Michelson interferometer Nominal resolution Inverse of the maximum optical path difference 1 δν N = OPD max High-resolution FTIR at PTB, Braunschweig, Germany EUMETRISPEC project spectral reference data for atmospheric measurements OPD max = 5 m δν N = cm -1 / 60 MHz Publishable JRP Summary Report for JRP ENV06 (EUMETRISPEC)

6 Instrumental Lineshape Function Insufficient resolution when δν N > ~FWHM/3 of absorption line Convolution with instrumental lineshape function Line broadening and intensity reduction Ringing on the absorption line Instrumental lineshape function (ILS) sinc function (for boxcar acquisition function) sinc OPD max ω S. P. Davis, M. C. Abrams, and J. W. Brault: Fourier transform spectrometry (Academic Press, 2001)

7 Instrumental Lineshape Function Insufficient resolution when δν N > ~FWHM/3 of absorption line Convolution with instrumental lineshape function Line broadening and intensity reduction Ringing on the absorption line Instrumental lineshape function (ILS) sinc function (for boxcar acquisition function) sinc OPD max ω δν N S. P. Davis, M. C. Abrams, and J. W. Brault: Fourier transform spectrometry (Academic Press, 2001)

8 Instrumental Lineshape Function Insufficient resolution when δν N > ~FWHM/3 of absorption line Convolution with instrumental lineshape function Line broadening and intensity reduction Ringing on the absorption line δν N < FWHM/3 Instrumental lineshape function (ILS) sinc function (for boxcar acquisition function) δν N > FWHM/3 sinc OPD max ω δν N S. P. Davis, M. C. Abrams, and J. W. Brault: Fourier transform spectrometry (Academic Press, 2001)

9 FTS with Optical Frequency Combs Advantages High spectral brightness no need to collimate light Spatial and temporal coherence long interaction length, better resolution High SNR in short acquisition times Retro reflectors v Beam splitter J. Mandon et al., Nat. Photonics 3, 99 (2009)

10 FTS with Optical Frequency Combs Advantages High spectral brightness no need to collimate light Spatial and temporal coherence long interaction length, better resolution High SNR in short acquisition times Input pulse train 1 f rep Retro reflectors v Beam splitter J. Mandon et al., Nat. Photonics 3, 99 (2009)

11 FTS with Optical Frequency Combs Advantages High spectral brightness no need to collimate light Spatial and temporal coherence long interaction length, better resolution High SNR in short acquisition times Input pulse train 1 f rep Retro reflectors v Beam splitter Output succession of bursts J. Mandon et al., Nat. Photonics 3, 99 (2009)

12 FTS with Optical Frequency Combs Advantages High spectral brightness no need to collimate light Spatial and temporal coherence long interaction length, better resolution High SNR in short acquisition times Input pulse train 1 f rep Retro reflectors v Beam splitter time domain c 4v f rep Output succession of bursts J. Mandon et al., Nat. Photonics 3, 99 (2009)

13 FTS with Optical Frequency Combs Advantages High spectral brightness no need to collimate light Spatial and temporal coherence long interaction length, better resolution High SNR in short acquisition times Input pulse train 1 f rep Retro reflectors v Beam splitter time domain c 4v f rep OPD domain c f rep Output succession of bursts J. Mandon et al., Nat. Photonics 3, 99 (2009)

14 Resolving the Comb Lines Mechanical FTS A few bursts limited by the interferometer size OPD max = 10 m δν N = 28 MHz 4 bursts I. Coddington et al., Phys. Rev. Lett. 100, (2008) J. D. Deschenes et al., Opt. Express 18, (2010) M. Zeitouny et al., Ann. Phys. 525, 437 (2013)

15 Resolving the Comb Lines Mechanical FTS A few bursts limited by the interferometer size OPD max = 10 m δν N = 28 MHz 4 bursts Dual comb spectroscopy Thousands of bursts limited by the memory size Resolution down to the comb linewidth I. Coddington et al., Phys. Rev. Lett. 100, (2008) J. D. Deschenes et al., Opt. Express 18, (2010) M. Zeitouny et al., Ann. Phys. 525, 437 (2013)

16 Resolving the Comb Lines Previously Resolution limited by the interferogram length Absorption features broader than nominal resolution and f rep

17 Resolving the Comb Lines Previously Resolution limited by the interferogram length Absorption features broader than nominal resolution and f rep Our method Comb line resolution from single-burst interferogram Absorption features narrower than nominal resolution and f rep ILS-free spectra c/f rep

18 Principle Arbitrary OPD max > c/f rep ILS P. Maslowski et al., submitted, arxiv

19 Principle Arbitrary OPD max > c/f rep 1/OPD max 1/OPD max ILS P. Maslowski et al., submitted, arxiv

20 Principle Arbitrary OPD max > c/f rep 1/OPD max 1/OPD max ILS P. Maslowski et al., submitted, arxiv

21 Principle Arbitrary OPD max > c/f rep OPD max = c/f rep 1/OPD max f rep 1/OPD max ILS f rep P. Maslowski et al., submitted, arxiv

22 Principle Arbitrary OPD max > c/f rep OPD max = c/f rep 1/OPD max f rep 1/OPD max ILS f rep P. Maslowski et al., submitted, arxiv

23 Interferograms comb bursts cw reference

24 Single-Burst Interferogram comb burst cw reference c/f rep

25 Single-Burst Interferogram comb burst cw reference c/f rep 2N points sampling positions λ ref /4

26 Single-Burst Interferogram comb burst cw reference c/f rep 2N points sampling positions λ ref /4 Optical path difference OPD max = 2N λ ref 4 c f rep

27 Discrete sampling Optical path difference OPD max = N λ ref 2 Sampling points k 2c Nλ ref Comb modes kf rep + f ceo

28 Discrete sampling Optical path difference OPD max = N λ ref 2 Sampling points k 2c Nλ ref Comb modes kf rep + f ceo Two issues: Imprecise step 2c Nλ ref f rep

29 Discrete sampling Optical path difference OPD max = N λ ref 2 Sampling points k 2c Nλ ref Comb modes kf rep + f ceo Two issues: Imprecise step 2c Nλ ref f rep Different offset f ceo

30 Interpolation Zero-padding of the time domain interferogram interpolate p points between two existing sampling positions

31 Interpolation Zero-padding of the time domain interferogram interpolate p points between two existing sampling positions 2N points

32 Interpolation Zero-padding of the time domain interferogram interpolate p points between two existing sampling positions 2N points M=pN points M=pN points

33 Interpolation Zero-padding of the time domain interferogram interpolate p points between two existing sampling positions 2N points M=pN points M=pN points p = 4

34 Fine-tuning the OPD Adding or removing a few points (< p) increases the accuracy of step to 1/(p+1)N 2N points M=pN points M=pN points

35 Fine-tuning the OPD Adding or removing a few points (< p) increases the accuracy of step to 1/(p+1)N 2N points M=pN points M=pN points Correct step f rep

36 f ceo Shift Multiplication in time domain f ceo shift in frequency domain e i2πf OPD ceo c

37 f ceo Shift Multiplication in time domain f ceo shift in frequency domain e i2πf OPD ceo c Correct step f ceo shift Correct absolute positions

38 Spectral Interleaving

39 f rep or f ceo scan to map the entire absorption lineshape Spectral Interleaving

40 f rep or f ceo scan to map the entire absorption lineshape Spectral Interleaving

41 Cavity-Enhanced OFCS in the NIR Er:fiber fs laser 250 MHz EOM λ/2 λ/4 Gas flow λ/4 F ~ L = 45 cm λ/2 PC FTS Er:fiber femtosecond laser: µm, 250 MHz repetition rate, 20 mw Cavity: finesse ~2000, length 45 cm, FSR 333 MHz

42 Cavity-Enhanced OFCS in the NIR Er:fiber fs laser 250 MHz EOM λ/2 λ/4 Gas flow λ/4 F ~ L = 45 cm λ/2 PC FTS Er:fiber femtosecond laser: µm, 250 MHz repetition rate, 20 mw Cavity: finesse ~2000, length 45 cm, FSR 333 MHz Effective comb line spacing in cavity transmission 1 GHz Comb-cavity matching FSR f rep

43 Cavity-Enhanced OFCS in the NIR λ/2 λ/4 Gas flow λ/4 Er:fiber fs laser 250 MHz EOM ~ f PDH F ~ L = 45 cm λ/2 f ceo control f rep control PDH Grating PC FTS Er:fiber femtosecond laser: µm, 250 MHz repetition rate, 20 mw Cavity: finesse ~2000, length 45 cm, FSR 333 MHz Effective comb line spacing in cavity transmission 1 GHz Two-point Pound-Drever-Hall (PDH) comb-cavity lock Comb-cavity matching FSR f rep

44 Cavity-Enhanced OFCS in the NIR λ/2 λ/4 Gas flow λ/4 Er:fiber fs laser 250 MHz EOM ~ f PDH F ~ L = 45 cm λ/2 f ceo control f rep control PDH Grating PC FTS Er:fiber femtosecond laser: µm, 250 MHz repetition rate, 20 mw Cavity: finesse ~2000, length 45 cm, FSR 333 MHz Effective comb line spacing in cavity transmission 1 GHz Two-point Pound-Drever-Hall (PDH) comb-cavity lock Fast-scanning FTS: OPD scanned at 0.8 m/s InGaAs autobalancing detector Comb-cavity matching FSR f rep

45 Cavity-Enhanced OFCS in the NIR Time domain interferogram P. Maslowski et al., submitted, arxiv

46 Cavity-Enhanced OFCS in the NIR Time domain interferogram Single-burst interferogram OPD max = 30 cm acquisition time 0.38 s δν N = 1 GHz P. Maslowski et al., submitted, arxiv

47 Cavity-Enhanced OFCS in the NIR Time domain interferogram Single-burst interferogram OPD max = 30 cm acquisition time 0.38 s δν N = 1 GHz Low-pressure CO 2 spectrum 10 interleaved spectra, f rep stepped by 500 Hz FWHM ~435 MHz No ILS distortion for δν N > FWHM 1% CO 2 in N 2 at 40 Torr P. Maslowski et al., submitted, arxiv

48 Cavity-Enhanced OFCS in the NIR Time domain interferogram Single-burst interferogram OPD max = 30 cm acquisition time 0.38 s δν N = 1 GHz Low-pressure CO 2 spectrum 10 interleaved spectra, f rep stepped by 500 Hz FWHM ~435 MHz No ILS distortion for δν N > FWHM 1% CO 2 in N 2 at 40 Torr P. Maslowski et al., submitted, arxiv

49 Cavity-Enhanced OFCS in the NIR Time domain interferogram Single-burst interferogram OPD max = 30 cm acquisition time 0.38 s δν N = 1 GHz Low-pressure CO 2 spectrum 10 interleaved spectra, f rep stepped by 500 Hz FWHM ~435 MHz 1% CO 2 in N 2 at 40 Torr No ILS distortion for δν N > FWHM 9-burst interferogram OPD max = 270 cm acquisition time 3.4 s δν N = 111 MHz P. Maslowski et al., submitted, arxiv

50 OFCS in the MIR Tm:fiber-laser pumped doubly-resonant MIR OPO: orientation-patterned (OP) GaAs crystal 3-6 µm, 418 MHz repetition rate, 30 mw dual-wavelength operation N. Leindecker et al., Opt. Express 20, 7046 (2012) K. F. Lee et al., Opt. Lett. 38, 1191 (2013)

51 OFCS in the MIR Tm:fiber-laser pumped doubly-resonant MIR OPO: orientation-patterned (OP) GaAs crystal 3-6 µm, 418 MHz repetition rate, 30 mw Multipass cell: 100 m effective path length FTS: OPD scanned at 10 mm/s InAsSb balancing detector dual-wavelength operation N. Leindecker et al., Opt. Express 20, 7046 (2012) K. F. Lee et al., Opt. Lett. 38, 1191 (2013)

52 OFCS in the MIR Fundamental CO band 13 interleaved spectra, f rep stepped by 200 Hz FWHM ~160 MHz 3.3 ppm CO in Ar at 11 Torr Single-burst interferogram OPD max = 72 cm acquisition time 16 s δν N = 418 MHz No ILS distortion for δν N > FWHM P. Maslowski et al., submitted, arxiv

53 OFCS in the MIR Fundamental CO band 13 interleaved spectra, f rep stepped by 200 Hz FWHM ~160 MHz 3.3 ppm CO in Ar at 11 Torr Single-burst interferogram OPD max = 72 cm acquisition time 16 s δν N = 418 MHz 11 Torr FWHM = 160 MHz 400 Torr FWHM = 1.56 GHz No ILS distortion for δν N > FWHM P. Maslowski et al., submitted, arxiv

54 OFCS in the MIR Fundamental CO band 13 interleaved spectra, f rep stepped by 200 Hz FWHM ~160 MHz 3.3 ppm CO in Ar at 11 Torr Single-burst interferogram OPD max = 72 cm acquisition time 16 s δν N = 418 MHz Pressure dependence of Lorentzian linewidth linear even for for δν N > FWHM CO in Ar, P7 line Pressure broadening coefficient ± GHz/atm P. Maslowski et al., submitted, arxiv

55 Conclusions Surpassing the OPD limit of FTS resolution OFC-based FTS with a maximal OPD matched to f rep Measurement of intensities of individual comb lines Undistorted absorption lines ILS-free FWHM below the nominal resolution High resolution spectra reduced instrument size (cm vs m) shorter acquisition time (s/min vs h) Demonstrated in the NIR (cavity-enhanced) and the MIR (multipass cell) Potential Hz level precision provided by the comb Compatible with commercial FTIR instruments P. Maslowski et al., submitted, arxiv

56 Acknowledgements Umeå University, Sweden Alexandra C. JOHANSSON Amir KHODABAKHSH Lucile RUTKOWSKI Nicolaus Copernicus University, Torun, Poland Piotr MASŁOWSKI Grzegorz KOWZAN IMRA America, USA Kevin F. LEE Martin E. FERMANN Andrew A. MILLS Christian MOHR Jie JIANG Funding sources Carl Tryggers Stiftelse

57 Thank you for your attention!