Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development V. Kubarev 1,2 , A. Bragin 1 , G. Sozinov 1 , E. Chesnokov 3 , P. Koshlyakov 3 1 Budker Institute of Nuclear Physics, Novosibirsk, Russia, 2 Novosibirsk State University, Novosibirsk, Russia, 3 Institute of Chemical Kinetics and Combustion, Novosibirsk, Russia
Outline • Introduction: – motivation of ultrafast single-shot spectroscopy – key elements of the spectroscopy • Free induction decay as basic of the spectroscopy : – exotic forms of FID signal • Different types of the spectroscopy: – Simple analytical spectroscopy a priory known spectra – Common spectroscopy a priory unknown spectra – Spectroscopy in magnetic field
Motivation and key elements Motivation: Ultrafast real-time spectroscopy is necessary in investigation of unrepeatable or single-pulse processes where classical well known methods spectroscopy based on sampling technology can’t be applied (loss information because of averaging). Key elements: • Powerful THz pulse source with qualitative beam (linear polarized gauss beams) – THz NovoFEL • Ultrafast detector – special Schottky diodes • Ultrafast direct oscilloscope – LeCroy 30 GHz (300 k$) V.V.Kubarev et al. “ Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016
Novosibirsk terahertz free electron laser (THz NovoFEL) User’s hall Accelerator hall 2004 Radiation parameters of THz NovoFEL: = 90 – 240 m, P average ≤ 500 W, P pulse ≤ 0.9 MW, (∆ / ) min = 2 10 -3 , f ≤ 22.4 MHz 178 ns Routine regime of THz NovoFEL: f = 5.6 MHz ≈ 60-150 ps V.V.Kubarev et al. “ Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016
Ultra-fast THz Schottky diode detector and oscilloscopes Unstable 15 Tektronix regime Sampling 50 GHz Power (a.u.) 10 Stable regime 5 0 THz 200 400 600 800 Time (ps) 0.25 LeCroy Unstable 0.2 Direct regime 30 GHz 0.15 Power (a.u.) 0.1 Stable regime 0.05 0 300 500 700 900 Time (ps) -0.05 V.V.Kubarev et al. “ Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016
Scheme of free induction decay radiation (FID) of molecules Free induction decay Exciting THz pulse (FID) radiation Beam quality of the FID radiation is the same as exciting beam (coherent excitation) Molecule in ground state Chesnokov E.N., Kubarev V.V., Koshlyakov P.V., and Kulipanov G.N. “ Direct observation of the terahertz optical free induction decay of molecular rotation absorption lines in the sub-nanosecond time scale ”, Appl Phys Lett 101 (2012) 131109-(1-4). V.V.Kubarev et al. “ Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016
Theoretical model of the free induction decay Basis: Lorentz dispersion theory of gases and Fourier transform: 2 i m m m n n in 1 A r i m 2 2 m m m 2 n i m A m 2 2 c c m m m m m k n 1 A r m 2 2 c c m m m 2 2 0 E E 0 exp 8 E E exp L exp i k L 1 L i k L i t E t E e e d 2 V.V.Kubarev et al. “ Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016
Free induction decay of rotational transitions in molecules Experimental setup: Trigger detector THz Beamsplitter Gas cell LeCroy 30 GHz Signal detector V.V.Kubarev et al. “ Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016
Very long free induction decay of HBr molecules Very long free induction decay of HBr molecules Exciting NovoFEL pulses 10 1 Power (arb.u.) ( ∆ f / f) min =(2-4) 10 -6 Free induction decay(FID) signal of HBr(0.04 torr) 0,1 0,01 1E-3 1E-4 0 50 100 150 200 t (ns) 100 79 Br +H 81 Br) THz spectral lines(J=4) (J=3) of HBr (H 0,8 Chesnokov E.N., Kubarev V.V., Koshlyakov P.V., Kulipanov G.N., 10 “ Very long terahertz free induction decay in gaseous hydrogen bromide” , Intensity (arb.u.) 0,6 Laser Phys. Lett. 10 (2013) 055701. 1 Power (arb.u.) 0,4 0,1 0,2 simulation 0,0 0,01 66,70 66,71 66,72 (Lorentz theory) -1 ) Wavenumber (cm experiment 1E-3 1E-4 0 20 40 60 Time (ns) V.V.Kubarev et al. “ Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016
Commensurate frequencies and simple analytical spectroscopy S 1(t) S 2(t) Probability of molecular identification is ≈ 99 % NO2 FID for wide laser line NO2 FID for narrow laser line (with Fabry-Perot interferometer) NO 2 Commensurate Echoes Chesnokov E.N., Kubarev V.V., and Koshlyakov P.V. “ Rotation commensurate echo of asymmetric molecules - Molecular fingerprints in the time domain ”, .Applied Physics Letters 105 (2014) 261107-(1-4). V.V.Kubarev et al. “ Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016
Giant light speed reduction in high-dispersion gas medium 1,2 1,0010 Empty D 2 O-HDO HBr 1,0 1,0005 0,8 1,0000 Power (a.u.) 0,6 n 0,9995 0,4 0,9990 0,2 0,9985 0,0 0,9980 69,0 69,5 70,0 0,0 0,5 1,0 1,5 2,0 2,5 t (ns) 1,00 Group light speed: d c V g ( 0 . 79 0 . 87 ) c 0,95 dn dk n n d 0,90 L.V. Hau, S. E. Harris, Z. Dutton, and C.H. Behroozi, “ Light speed reduction to 17metres per second in an ultracold atomic gas ”, Nature , v. 397, pp. 594-598, 1998. 0,85 Sample: T = 450 nK, L = 229 m 0 20 40 60 80 -1 cm V.V.Kubarev et al. “ Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016
Scheme of the ultrafast time-domain spectrometer 1 i ( t ( ) ) E ( t , ) E ( ) e d P 3 (t) 0 0 2 Ultrafast Schottky P 1 (t) diode detectors Re( E ( t ,φ 0 )) Im( E ( t ,φ 0 )) Cell with tested gas Mirror and moving P 4 (t) or free space polarizer shifted by /4 Im( E ( t, 0)) = Re( E ( t, π /2)) Two Mach-Zehnder P 2 (t) interferometers Re( E ( t, π /2)) Re( E ( t, 0)) E- polarization FEL radiation Cell with reference gas or Fabry-Perot interferometer (frequency standart) Four-channel scheme: Two-channel scheme: ( 0 ) ( ) P ( t ) P ( t ) 1 2 E ( t ) E ( t ) cos ( t ) ~ ; E ( t ) E ( t ) cos ( t ) ~ P ( t ) P ( t ) ; x P ( t ) x 1 , 2 ref ref ( / 2 ) ( 3 / 4 ) E ( t ) E ( t ) sin ( t ) ~ P t P ( t ) . P ( t ) P ( t ) y 3 , 4 ref 3 4 E ( t ) E ( t ) sin ( t ) ~ . y P ( t ) ref V.V.Kubarev et al. “ Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016
Ultrafast time-domain spectrometer (UTDS) V.V.Kubarev et al. “ Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016
Experimental spectra and spectral resolution 8 60 000 D 2 O/H 2 O vapor (0.8 Torr, 200 mm), HDO f 0 = 2.122416 THz, Spectral intensity (arb.u.) inverse spectral resolution - 8 10 -5 , 50 000 6 measuring time - 6 ns. Spectral resolution 40 000 4 30 000 D 2 O 2 D 2 O 20 000 0 10 000 -8 -6 -4 -2 0 2 4 6 8 f (GHz) 0 0 5 10 15 20 25 7 CH 3 OH (0.2 Torr, 600 mm) Measuring time (ns) 6 f 0 =2.122416 THz, 2 000 5 inverse spectral resolution - 1.8 10 -5 , 4 1 800 measuring time - 25 ns. 3 1 600 Spectral intensity (a.u.) Spectral resolution 2 1 400 1 0 1 200 -8 -6 -4 -2 0 2 4 6 8 0,5 1 000 0,4 800 0,3 600 0,2 400 0,1 200 0,0 0 -8 -6 -4 -2 0 2 4 6 8 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 f (GHz) Measuring time (ns) V.V.Kubarev et al. “ Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016
Modification of the ultrafast time-domain spectrometer for one-pulse diagnostics of NovoFEL radiation P 3 (t) P 2 (t) Ultrafast Schottky diode detectors Mirror and moving polarizer shifted by / 4 P 5 (t) P 4 (t) P 1 (t) E-field polarization NovoFEL radiation Fabry-Perot interferometer tuned at fundamental mode V.V.Kubarev et al. “ Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016
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