Filling the THz Gap GWYN P. WILLIAMS. Jefferson Lab Jefferson Avenue - MS 7A Newport News, VA

Transcription

1 Filling the THz Gap GWYN P. WILLIAMS Jefferson Lab Jefferson Avenue - MS 7A Newport News, VA gwyn@mailaps.org CASA Seminar, Novemer 14, 2003

2 x ma Diff. Limit GROWTH IN SYNCHROTRON X-RAY SOURCE BRIGHTNESS (Photons/sec/0.1%bw/sq.mm/mrad 2 ) rd. Gen. original design What s new? nd. Gen. 1st. Gen. Synch. Rad. Cray T Short pulses/ Multiparticle coherence CDC 6600 Cray 1 GROWTH IN LEADING EDGE COMPUTING SPEED (Millions of operations/sec) Calendar Year Near-field

3 The THz Gap Many important dynamical processes occur in the THz region (5 mev). Superconducting band-gaps, protein conformational modes, phonons. With high coherent power the key niche areas are non-linear dynamics and imaging.

4 THz Brief History After Nichols left Berlin, Rubens continued the work, and in 1900 he isolated wavelengths of 6THz (50 microns) and made careful measurements which he gave to Max Planck who derived the Radiation Law. Planck wrote in 1922 Without the intervention of Rubens the formulation of the radiation law, and consequently the formulation of quantum theory would have taken place in a totally different manner, and perhaps even not at all in Germany.

5 The Paper That Started it all. 1981

6 1 micron

7 Backing up.auston Switch for producing THz light 2 2 2ea Larmor's Formula: Power = (cgs units) 3 3c Auston, D.H., Cheung, K.P., Valdmanis, J.A. and Kleinman, D.A., Phys. Rev.Letters (1984).

8 Radiation from Accelerated Electron Electric field goes linearly in the electric charge and the acceleration electron field - so intensity (power) goes like e 2 a 2 But units of power are: Power Force Distance Time MLT 2 L 2 3 acceleration = = ML T T Now for an electric charge, force is e 2 /L 2, so we can derive units for e thus: = e L 2 = MLT 2 2 So e 2 a 2 has units of :ML 3 T -2 L 2 T -4 = ML 5 T -6 And if we divide by c 3, or L 3 T -3, we get ML 2 T -3.

9 Radiation from Accelerated Electron Also we note that radiation is emitted in only 2 out of 3 directions, so we have a 2/3 factor, yielding: Larmor s Formula 2 2 Power = 2ea 3 3 Noting that the units of power are ML 2 T -3, and noting that M goes like gamma, L goes like 1/gamma and T goes like gamma in the moving frame, in the rest frame the relativistic version is : 2 2 Power = 2eaγ4 3 3 N.B. Radiated energy and elapsed time transform in the same manner under Lorentz transforms c c

10 Comparing Coherent THz Synchrotron and Conventional THz Sources 2 2 2ea 4 Larmor's Formula: Power = (cgs units) 3 γ 3c a=acceleration c=vel. of light γ=mass/rest mass a ~100 V THz fsec laser GaAs pulse 100V 6 E = = 10 V 4 10 m m F 10 V 10 ( 3 10 ) = = = 2 6 m.5mev /c m 2 sec GaAs fsec laser pulse e - -> 40 MeV ρ c (3 10 ) 17 m a = = 10 ρ 1 if ρ = 1 m γ = = sec THz and 80 10!!!! 2

11 Synchrotron Radiation Generation e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e-

12 Synchrotron Radiation Generation electron(s) Electric field time E/N Intensity E 2 N THz super-radiant enhancement freq. (1/time) W.D. Duncan and G.P. Williams, Infra-red Synchrotron Radiation From Electron Storage Rings, Applied Optics 22, 29l4 (1983).

13 Synchrotron Radiation Generation - actual situation Statistics of an electron bunch in a storage ring Time Scale 1 Time Scale 2 Hirschmugl, Sagurton and Williams, Physical Review A44, 1316, (1991).

14 Coherent Synchrotron Radiation Generation - theory 2 f ω eiω nz ˆ / c S z dz = nr(t) ˆ. / iω t c d2i 2 e2 2 N[1 f( )] N f( ) ω / = ω + ω nˆ β nˆ e dt dω dω 4π 2c f(ω) is the form factor the Fourier transform of the normalized longitudinal particle distribution within the bunch, S(z) REFERENCES S.L. Hulbert and G.P. Williams, Handbook of Optics: Classical, Vision, and X-Ray Optics, 2nd ed., vol. III. Bass, Michael, Enoch, Jay M., Van Stryland, Eric W. and Wolfe William L. (eds.). New York: McGraw-Hill, (2001). S. Nodvick and D.S. Saxon, Suppression of coherent radiation by electrons in a synchrotron. Physical Review 96, (1954). Carol J. Hirschmugl, Michael Sagurton and Gwyn P. Williams, Multiparticle Coherence Calculations for Synchrotron Radiation Emission, Physical Review A44, 1316, (1991). 2

15 Synchrotron Radiation - so what s new here? radio-freq. cavity

16 Synchrotron Radiation - so what s new here? radio-freq. cavity Showstopper. Solution.. 3 Energy GeV at Recovery 100 ma is 300 Megawatts!!!!!

17 THz Setup on JLab IR-DEMO FEL FTIR System FTIR System e - We measured the bend-magnet synchrotron radiation right before the FEL, when the beam is maximally compressed.

18 THz Setup on JLab IR-DEMO FEL Crystal quartz window Collimating optic Nicolet Nexus 670 FTIR bench LHe cooled Si bolometer detector

19

20 October 2002

21 THz Expt and Calculation Frequency (THz) Diffraction losses Measured Calculated (500fs bunch length) ~ 20 Watts integrated Watts/cm Carr, Martin, McKinney, Neil, Jordan & Williams Nature 420, 153 (2002) Frequency (cm -1 )

22 Coherent THz vs. Current Intensity (Arb. Units) Integrated THz Intensity (Arb. Units) Measured intensity Measured Intensity Fit N 2 to (Current) 2 Fit Beam Current (µa) Current (µa) 50 µa 80 µa 105 µa 110 µa 170 µa 230 µa Wavenumbers (cm -1 )

23 Polarization of Coherent THz Measured Intensity (Arb. Units) 3500 I = 0.04 ma Polarizer Horizontal Polarizer Vertical Expected polarization ratio for 60 mrad port at 30 cm -1 is 6:1. We observed 5:1. Good agreement Wavenumbers (cm -1 )

24 Why do this? Terahertz Imaging Clery, Science (2002)

25 IR Spectroscopy & Dynamics is based on Vibrations Simple molecule More complicated molecule - protein Slide courtesy Paul Dumas, LURE, Orsay, France

26 Protein Structure / Folding Dynamics Amide I Secondary Structure Assignments: β-sheet 1644 extended coil (D 2 O) α-helix helix anti-parallel β-sheet, β-turn 0.2 Carboxypeptidase β-turn β-sheet Absorbance extended coil α-helix Frequency (cm -1 )

27 Protein Folding Dynamics - Silk Fiber Formation SCAN PARAMETERS: %T: silk fibroin on BaF 2 disk 32 scans at 200 KHz (2.3 sec) 4 cm -1 resolution MCT detector Absorbance random coil beta sheet 10 sec 30 sec 90 sec 180 sec Frequency Lisa Miller, Mark Chance et al.

28 THz Spectroscopy Anthrax proxy DNA Globus et al. University of Virginia J. App. Phys (2002)

29 THz Imaging A tooth cavity shows up clearly in red. Teraview Ltd.

30 The Promise of THz novel imaging

31 The Promise of THz novel imaging

32 THz Imaging Basal cell carcinoma shows malignancy in red. Teraview Ltd.

33 Terahertz computerized tomography 3cm Turkey Bone Test Object Ferguson et. al. Phys. Med. Biol (2002)

34 So where are we going at JLab with THz?

35 FEL upgrade, phase 1 THz light port Jefferson Lab s new ERL/FEL/THz source Turned-on June 2003!!

36 JFEL THz Port Description Final Rev. 1 Dated s M1 to dimad start of bend = 667mm ρ=1.2 meter 0 o Penetration location 1040 mm from dimad start of bend point. 85 mr 0 o 3.58 o 50 mr mr M1 (110 x 155) mm 10.2 o = 173 milliradians 146 mr View from the back of M1 looking at beam 60 Beamline Center Line to be: 2 0 tangent, 35 mrads from zero degrees 7/24/03 GPW This puts F1=667-( )=625

37 JFEL THz Port Description Final Rev. 1 Dated Dimensions in mm not to scale M1 110 x 155 M2 120 x 170 M3 183 x 258 M4 183 x 258 M2 (plane) Neil/GPW M4(ellipsoid) F1 F M3 ellipsoid M1(ellipsoid) F Floor 2480 Ceiling 2330 e-beam

38 SRW Calculation of light on screen 3.0 m from source by Paul Dumas Phot/s/0.1%bw/mm 2 1.0x x Spectral Flux / Surface vertical cut 0-0.2m Vertical Position Vertical Position Spectral Flux / Surface at λ=100 µm 3 m from downstr. BM Edge m m Horizontal Position -0.2m Horizontal Position Flux after 1-st Aperture: e+13 Photons/s/.1%bw

39 What is Edge Radiation? Dipole Radiation Edge Radiation Edge Radiation is light emitted as the electrons enter the fringe field of a dipole magnet. For long wavelengths the fringe field maybe treated as an impulse acceleration. Thus edge radiation has characteristics similar to transition radiation. In the far field approximation for a single edge the angular spectral flux is white up to a cutoff determined by the details of the fringe and is given by, df dω = α ω ω I eπ ( γ θ ) 2 Reference: R.A. Bosch, Nuclear Instr. & Methods A (1999). 2 γ 4 θ 2 d F dw gq

40 E = ec i + R c dτ ω n [( n βe ) βe ] cr γ + ( n βe ) exp[ ω( τ / )] (1 nβ ) 2 e R Full formula

41 What does edge Radiation look like? Daresbury Lab Ann Rep 1984/5

42 Two Edges Interfere Screen Edge 1 Edge 2 L Interference of Two Edges in Far Field Near Field Calculation of Two Edges using SRW (Chubar& Elleaume, ESRF) df dω 2 df dω 1 df 4 dω πl 1 Exp 2 λγ 1 Sin 2 πl 2λγ 2 ( γ θ ) ( 2 2) 1+ γ θ 2 Spectrum is no longer white Opening angle depends on λ

43 JLab s new THz Beamline

44 JLab s new THz Beamline Watts/cm E-3 1E-4 1E-5 1E-6 1E-7 1E-8 1E-9 Frequency (THz) Jlab Demo 5mA 100pc 500 fsecs fwhm 60hX60v Synchrotron radiation (NSLS, Brookhaven) 800 ma 90X K Black Body 10 mm 2 JLab Upgrade 135 pc 75 MHz (10mA) 300fs 150x150 Integrated Intensity Watts 1E Frequency (cm -1 )

45 JLab s new THz Beamline Watts/cm E-3 1E-4 1E-5 1E-6 1E-7 1E-8 1E-9 Frequency (THz) JLab FEL - THz Port 75 MHz 135 pc (10 ma) 150 x 150 mr Int. Power 100 fs FWHM 1.1kW 400 fs FWHM.26kW 800 fs FWHM.11kW 1E Frequency (cm -1 )

46 Flux (Watts/cm -1 ) E-3 1E-4 1E-5 1E-6 1E-7 1E-8 1E-9 1E-10 1E-11 Brightness of IR Sources Energy (mev) JLab THz Synchrotrons Globar 1E Wavenumbers (cm -1 ) JLab FEL Table-top sub-ps lasers THz proof of principle: Carr, Martin, McKinney, Neil, Jordan & Williams Nature 420, 153 (2002) FEL proof of principle: Neil et al. Phys. Rev.Letts 84, 662 (2000)

47 Thanks to. George Neil, Fred Dylla and the Jefferson Lab FEL Team Larry Carr (Brookhaven National Laboratory) Lisa Miller (Brookhaven National Laboratory) Carol Hirschmugl (UW Milwaukee) Paul Dumas (University of Paris, France) Oleg Chubar (Soleil project, Saclay, France) Mike Martin (Berkeley Lab) Wayne McKinney (Berkeley Lab) Funded by United States DOE, DOD DE-AC05-84-ER40150 TJNAF