Single-pulse high-resolution spectroscopy on NovoFEL: methods, - - PowerPoint PPT Presentation

Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development

• V. Kubarev 1,2, A. Bragin1, G. Sozinov1,
• 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

V.V.Kubarev et al. “Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016

Motivation: Ultrafast real-time spectroscopy is necessary in investigation

• f

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$)

Accelerator hall User’s hall

Novosibirsk terahertz free electron laser (THz NovoFEL)

2004

Radiation parameters of THz NovoFEL:

 = 90 – 240 m, Paverage ≤ 500 W, Ppulse ≤ 0.9 MW, (∆/)min= 210-3, f ≤ 22.4 MHz

Routine regime of THz NovoFEL: f = 5.6 MHz

178 ns ≈ 60-150 ps

V.V.Kubarev et al. “Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016

5 10 15 200 400 600 800

Time (ps) Power (a.u.)

• 0.05

0.05 0.1 0.15 0.2 0.25 300 500 700 900

Time (ps) Power (a.u.)

Unstable regime Stable regime Unstable regime Stable regime

Tektronix Sampling 50 GHz LeCroy Direct 30 GHz

Ultra-fast THz Schottky diode detector and oscilloscopes

THz

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 (FID) radiation Exciting THz pulse Molecule in ground state

V.V.Kubarev et al. “Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016

Beam quality of the FID radiation is the same as exciting beam (coherent excitation)

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).

Theoretical model of the free induction decay

         

2 2 2

1

m m m r i m m m m

i n n in A                  



   

2 2 2 i m m m m m

n A c c            



       

2 2

1

m m r m m m m

k n A c c                



   

2 2 0 exp

8 E E                

       

exp exp E E L i k L                  

   

   

1 2

L i k L i t

E t E e e d

   

  

     

  



Basis: Lorentz dispersion theory of gases and Fourier transform:

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:

Signal detector LeCroy 30 GHz Gas cell Beamsplitter Trigger detector

THz

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

50 100 150 200 1E-4 1E-3 0,01 0,1 1 10

Power (arb.u.) t (ns)

Exciting NovoFEL pulses Free induction decay(FID) signal of HBr(0.04 torr)

20 40 60 1E-4 1E-3 0,01 0,1 1 10 100

66,70 66,71 66,72 0,0 0,2 0,4 0,6 0,8 Intensity (arb.u.) Wavenumber (cm

• 1)

THz spectral lines(J=4)(J=3) of HBr (H

79Br +H 81Br)

Power (arb.u.) Time (ns) simulation (Lorentz theory) experiment

(∆f / f)min=(2-4)10-6

Chesnokov E.N., Kubarev V.V., Koshlyakov P.V., Kulipanov G.N., “Very long terahertz free induction decay in gaseous hydrogen bromide”, Laser Phys. Lett. 10 (2013) 055701.

Very long free induction decay of HBr molecules

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

NO2

NO2 FID for wide laser line NO2 FID for narrow laser line (with Fabry-Perot interferometer) Commensurate Echoes

Probability of molecular identification is ≈ 99 % S1(t) S2(t)

V.V.Kubarev et al. “Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016 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).

Giant light speed reduction in high-dispersion gas medium

69,0 69,5 70,0 0,9980 0,9985 0,9990 0,9995 1,0000 1,0005 1,0010

n

20 40 60 80 0,85 0,90 0,95 1,00

n

cm

• 1

0,0 0,5 1,0 1,5 2,0 2,5 0,0 0,2 0,4 0,6 0,8 1,0 1,2 Power (a.u.)

t (ns)

Empty D2O-HDO HBr

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. Sample: T = 450 nK, L = 229 m

c d dn n c dk d Vg ) 87 . 79 . (        

Group light speed:

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

P1(t) Ultrafast Schottky diode detectors Cell with tested gas

• r free space

Cell with reference gas or Fabry-Perot interferometer (frequency standart) FEL radiation Mirror and moving polarizer shifted by /4 P2(t) P3(t) P4(t) Two Mach-Zehnder interferometers E-polarization

; ) ( ) ( ) ( ~ ) ( cos ) ( ) (

) ( 2 ) ( 1

t P t P t P t t E t E

ref x 

   . ) ( ) ( ) ( ~ ) ( sin ) ( ) (

) 4 / 3 ( 4 ) 2 / ( 3

t P t P t P t t E t E

ref y  

  

Four-channel scheme:

; ) ( ) ( ~ ) ( cos ) ( ) (

2 , 1

t P t P t t E t E

ref x

  

 

. ) ( ~ ) ( sin ) ( ) (

4 , 3

t P t P t t E t E

ref y

  

Two-channel scheme:

V.V.Kubarev et al. “Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016



 



    

    d e E t E

t i ) ) ( (

) ( 2 1 ) , (

Re(E(t,φ0)) Im(E(t,φ0)) Im(E(t,0)) = Re(E(t,π/2)) Re(E(t,0)) Re(E(t,π/2))

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

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 200 400 600 800 1 000 1 200 1 400 1 600 1 800 2 000

Spectral resolution Measuring time (ns)

Experimental spectra and spectral resolution

• 8
• 6
• 4
• 2

2 4 6 8 2 4 6 8

D2O Spectral intensity (arb.u.)

f (GHz)

HDO D2O

• 8
• 6
• 4
• 2

2 4 6 8 0,0 0,1 0,2 0,3 0,4 0,5

• 8
• 6
• 4
• 2

2 4 6 8 1 2 3 4 5 6 7 Spectral intensity (a.u.) f (GHz)

5 10 15 20 25 10 000 20 000 30 000 40 000 50 000 60 000

Spectral resolution Measuring time (ns)

D2O/H2O vapor (0.8 Torr, 200 mm), f0 = 2.122416 THz, inverse spectral resolution - 810-5, measuring time - 6 ns. CH3OH (0.2 Torr, 600 mm) f0 =2.122416 THz, inverse spectral resolution - 1.810-5, measuring time - 25 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

P2(t) P4(t) P3(t) P5(t) P1(t)

Fabry-Perot interferometer tuned at fundamental mode Ultrafast Schottky diode detectors Mirror and moving polarizer shifted by /4 E-field polarization NovoFEL radiation

V.V.Kubarev et al. “Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016

Single-pulse spectroscopy of NovoFEL radiation

Stabilized regime

Spectral width (FWHM) – 2·10-3 (4 GHz) – Fourier limit for 100 ps pulse f0 = 2.12 THz, Inverse spectral resolution – 1.210-3, Measuring time – 0.4 ns.

• 30
• 20
• 10

10 20 30 0,0 0,2 0,4 0,6 0,8 1,0 Spectral intensity (arb.u.) Df (GHz)

Regime of moderate side-band (SB) instability

Integral spectral width – 5·10-3 (10 GHz) f0 = 2.12 THz, Inverse spectral resolution – 1.210-3, Measuring time – 0.4 ns. Pulse with four SB-modes

• ne pulse

ave of 500 pulses most different pulses Pulse with two SB-modes Fourier spectrometer IFS-66vs SB-modes

Regime of strong SB-instability

Integral spectral width – 9·10-3 (18 GHz) f0 = 2.12 THz, Inverse spectral resolution – 1.210-3, Measuring time – 0.4 ns.

• 40
• 30
• 20
• 10

10 20 30 40 0,0 0,2 0,4 0,6 0,8 1,0

Spectral intensity (a.u.)

 f (GHz)

Fourier spectrometer IFS-66vs Pulse without SB-modes Pulses with five SB-modes V.V.Kubarev et al. “Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016

Non-Faraday rotation of polarization

FID radiation of paramagnetic NO molecules (gas cell - 400 mm, 2 Torr) : Scheme of the experiment:

W

+ =

 W  W NO W f(t)

10 20 30 40 50 60

Shifted FID signals (a.u.) time (ns)

H = 720 Gs H = 360 Gs

H = 0 Gs

f(t) = 

Linear polarized FEL radiation Gas cell inside solenoid Closed polarizer Ultra-fast Schottky diode detector

Features of the non-Faraday rotation of coherent FID radiation :

• large-scale effect
• rotation angle is time function

Applications:

• high resolution molecular spectroscopy

( H = 30-70 kGs, superconducting solenoid)

• ultrafast high-sensitive spectroscopy of

short-lived chemical radicals

V.V.Kubarev et al. “Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016 Chesnokov E.N., Kubarev V.V., Koshlyakov P.V., Getmanov Ya.V., Shevchenko O.A. “Non-Faraday rotation of the free induction decay in gaseous NO”, Chemical Physics Letters 636 (2015).

NO2 FID in magnetic fields. Sensitive spectroscopy

V.V.Kubarev et al. “Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016

10 20 30 40 0,0000 0,0001

Calculation H=120Gs Y pol , arb. un. t, nsec Experiment H=0 Experiment H=120Gs

P(NO2)= 1 Torr L = 40 cm Fully closed polarizer Slightly open polarizer

Ultrafast spectroscopy in strong magnetic field

V.V.Kubarev et al. “Single-pulse high-resolution spectroscopy on NovoFEL: methods, applications and development” BINP, Novosibirsk, Russia SR-2016

Poster Session: “Superconducting solenoid for superfast THz spectroscopy”

• A. Bragin, S. Khruschev, V. Kubarev, N. Mezentsev, V. Shkaruba,
• G. Sozinov, V. Tsukanov

Liquid-free superconducting 6 T solenoid

Thank you for attention !