Design study of compact Compton X-ray sources for life sciences applications

1. Design study of compact Compton X-ray sources for life sciences applications E.G.Bessonov, M.V.Gorbunkov, B.S.Ishkhanov, P.V.Kostryukov, Yu.Ya.Maslova, A.A.Mikhailichenko, V.I.Shvedunov, V.G.Tunkin, A.V.Vinogradov Lebedev Physical Institute, Moscow, Russia Moscow State University, Moscow, Russia Cornell University, USA

2. Design study of compact Compton X-ray sources (LEXGs) • Introduction • Pulsed operation mode for life sciences • Circulators • Laser unit • Summary

3. ћωL=1.16eV laser e- X-Rays hω=33keV Compton X-ray source = laser-electron X-ray generator (LEXG) utilizing the process of relativistic Compton scattering Total # of X-ray photons at relativistic Compton scattering: - transverse beam sizes, Valid if

4. EL ≤ 10 mJ, 15 ps, λ = 1.06 μm 1 nC, 10 ps, Ee= 43 MeV e - bunch “Building brick”collision: e-bunch(1nC) + laser pulse (10mJ) Transverse beam size: 1 nC bunch + 10 mJ pulse N0=5•106X-ray photons collimated into ~ 10 mrad. The goal is to arrange “building brick” collisions in a compact and cost-effective system.

5. CW mode LEXG operation #1 X-ray pulse 5*106 ph linac e- bunch 1 nC laser pulse 10 mJ Circulator and storage ring pave a way for practical X-ray applications of relativistic Compton scattering. #2 X-ray pulses @ 10 ns period linac laser pulses @ 1mcs period e- multibunch, 10 ns period optical circulator, nC = 100 #3 e- storage ring, ne = 104 X-ray pulses @ 10 ns period linac e-bunch laser pulses @ 1mcs period optical circulator, nC = 100

6. 35 MeV LINAC Beam dump e KICK INF e IP R1.064 < 1% R0.53 >99.9% λ2 t X-rays RFC T = 2 μs τ< 15ps λ2= 0.53μm R1.064 < 1% R0.53 >99.9% T = 10 ns c λ1= 1.064 μm Nonlinear crystal R1.064 < 1% R0.53 >99.9% R1.064 < 1% R0.53 >99.9% 200 μs Laser-electron X-ray Generator for EXAFS applications: circulator based on second harmonic generation in a high-Q cavity λ1 t τ < 15 ps s s T = 2 μ T = 2 μ

7. LEXG designed for K-edge subtraction imaging for human angiography 30Hz,1nC, 43 MeV LINAC Beam dump e KICK INF e IP 1.5•1012ph / 4.5•1013sec-1. X-rays RFC R>99.9% R>99.9% t T = 1 μs R>99.9% τ < 15 ps Pockels cell 1 P1 R>99.9% Pockels cell 2 T = 10 ns c λ2 <1 ms 1 ms 1.5-2 ms P2 λ λ 1 2 30Hz, 900W, train length - 1ms, 103 pulses, train energy - 30J. t τ < 15 λ1 ps s s T = 1 μ T = 1 μ Pulsed operation mode.

8. Compact Storage Ring with Injector 50MeV Linac Achromatic bend 1350mm 1630mm Calculations with “BEAMOPTICS” code. Dispersion at IP=0 8 8

9. CW Laser: cw picosecond pulses and cavity Pulsed Laser: repetitive trains of picosecond pulses and circulator Cw picosecond pulses (1-10W is commercially available) High finesse mirrors Locking feedback Mirror surface distortion at high light power (up to 1 MW required) Principles for effective enhancement Circulator materials Stable trains (up to 105) of picosecond laser pulses

10. laser pulses added coherently no intracavity elements laser pulse repetition rate equals to the cavity round-trip time build-up time of intracavity light power increases with the cavity enhancement factor increase possibility to operate with phase non-coherent laser pulses optical switch providing trapping of laser pulses in the interaction chamber laser pulse repetition rate is much above the circulator round-trip enhancement is obtained by the storage of a laser pulse in trapped state by optical switch CavityCirculator

11. Optical circulator facilitates multiple interaction of each laser picosecond pulse with electron bunches in the interaction chamber providing at least 100 fold increase in X-ray photon output per one laser photon. Fig. 1. Optical circulator based on intracavity Pockels cell Fig. 2. Optical circulator based on intracavity second harmonic generation The enhancement factor of optical cavity is expected to be higher than that of a circulator. However, the important advantage of the latter is the possibility to operate with phase non coherent laser pulses. Circulator is well adapted to linac multibunch beams.

12. Optical circulator based on Pockels cell: BBO Pockels cell in the position “on” directs laser pulse in the circulator cavity and in position “off” (in the absence of an electric field) saves it in the trapped stage. Besides losses induced by discrete optical elements Pockels cell in the “off” position has additional ones. They are caused by a depolarization in electro-optic (E-O) crystal. Therefore the problem in the Pockels cell based circulator design is to choose a suitable electro-optic material. BBO offers the possibility to increase the enhancement factor of optical circulators based on intracavity Pockels that is now equal to several tens. But the chance to overcome two orders of magnitude enhancement by E-O devices is still questionable. Best candidate: Beta-Barium Borate (b-BaB2O4 ) (BBO): high damage threshold 10 GW/cm2 (1.3 ns) @ 1064 nm low insertion loss (absorption coefficient < 0.1%/cm) @ 1064 nm withstands average powers in excess of 20 kW/ cm2 (CW) @ 1064 nm.

13. Passive optical circulator based on intracavity second harmonic generation: LBO Passive circulator does not require any high voltage unit synchronized with the laser pulses. Scheme includes only a nonlinear crystal in the cavity thus providing small insertion losses. • Lithium Triborate (LiB3O5) (LBO): a nonlinear crystal with excellent physical and optical properties • the highest bulk damage threshold among all known nonlinear optical crystals • extremely low absorption coefficient @ 1.06 and 0.53 µm (<0.01%/cm) • allows non-critical phase-matching for 1.0-1.3 µm Type I SHG, relatively large angular acceptance bandwidth, reducing the beam quality requirements for source lasers • practically lossless circulator operation with Brewster angle (Type I SHG) Completely passive circulator (with possibly thin LBO crystal) is the most promising for LEXG.

14. M2 Modp Modn D P M1 AM CCp CCn F OD To improve stability of quasi CW train and significant ps pulse shortening we suggest to add positive feedback besides commonly used negative feedback loop. (positive feedback action is one round-trip later than negative) Positive and negative feedback loops controlled picosecond lamp pumped YAG-Nd laser. AM active laser medium; M1, M2 cavity mirrors; P polarizer; D diaphragm; Modn, Modp electrooptic modulator sections of negative and positive feedback loops; CCn, CCp positive and negative feedback control circuits; OD positive feedback optical delay line; F neutral density filter. Train of stabilized picosecond pulses Time scale 20 s per point Laser pulse measured by streak-camera and its fit bypulse shape.

15. Optoelectronic feedback control circuit R1 R2 UPE UST Cm PE Rm C1 C2 Laser Pockels PE – photo element; Rm, R1, R2 – resistors; C1, C2, Cm – capacitors; UPE – photo element bias voltage, UST – Pockels cell bias voltage RmCm – feedback time constant, T –Pockels cell transmission.

17. Stabilization problem was solved – trains can be used for multibunch system. For pulses with 2 mcs period, we have to cut or preshape train. Pulsed operation mode for life sciences. To observe breath, heart beat and other physiological motion, the exposure 1 - 0.1 msec and the rate of frames ν= 30 Hz are needed. In LEXG this is achieved by collision of pulse trains. ν= 30Hz 17

18. Experiments: joint NFB and PFB control, LiTaO3 crystal To achieve preshaping with mcs period we suggest to add positive feedback besides commonly used negative feedback loop (negative feedback comes one round-trip later than positive). En G2REn-1 G2REn-1 - En Fig. Millisecond lamp pumped picosecond YAG-Nd laser designed for submcs scale pulsations. AM active laser medium; M1, M2 cavity mirrors; P polarizer; D diaphragm; MT mirror telescope; Mod electrooptic modulator; CC feedback control circuit.

19. a b Millisecond traces: (a) stabilized train and (b) pump power 0.5 ms/div (discharge time is 3.9 ms) a

20. Experiments: regular and chaotic pulsation development, LiTaO3 crystal Fig.1. Millisecond traces: 0.5 ms/div, vertical scales are equal a 0.4 s b 0.49 s c 1.7s d f pulsation development Fig.2. Microsecond time-scale oscilloscope traces in regular and chaotic regimes (a-e) and the corresponding Fourier transforms (f-g). g e By increasing the pump power we observed regimes of regular pulsations with controlled period from 25 up to 75 Tr as Ustwas decreased from 0.3U/4 to 0.05U/4.

21. Experiments: resonant shear modes excitation in DKDP crystal v =1.64x105 cm/s d = 0.8cm [1] R.A. Sykes, Bell Sys. Tech. J. 23, 52 (1944) [2] Ekstein H. Free Vibration of Anisotropic Bodies. Phys. Rev., V.66, No. 5 and 6, 1944. Fig. 1. Shear vibrations of a square plate ((a)observations [1] and (b) calculation [2]). Fig.2. Pockels cell transmission at the first 4 shear mode resonances. Fig.3. Millisecond lamp pumped picosecond YAG-Nd laser designed for mcs scale pulsations. AM active laser medium; M1, M2 cavity mirrors; P polarizer; D diaphragm; MT mirror telescope; Mod electrooptic modulator; CC feedback control circuit.

22. The development of regular mcs pulsations and a pulsation fine time structure

23. Diode pumped picosecond laser Scheme of a picosecond diode-pumped laser controlled by a combination of NFB and PFB: AM – active medium, M1, M2, M3 – high reflector mirrors, M4 – output mirror, OD1, OD2 – optical delay lines, P – polarizer, EOM – low-voltage electro-optical modulator, BS – beam splitter. Train of stabilized picosecond pulses.

24. Laser unit for life science applications design summary • System with two feedbacks: Period controlled by the relative feedback sensitivity, up to 75 roundtrips • System with two feedbacks and harmonic modulation: Period controlled by the external harmonic modulation and potentially two times larger • The systems differ in pulsation shape and the scenarios of transition to chaos

25. Summary • The LEXG design for medical applications differs significantly from the Compton X-ray source for cw mode [Zh. Huang, R.D. Ruth]: • repetitive laser pulse trains instead of cw laser • circulator instead of cavity • LEXG in a pulsed mode enables on-line investigation of live objects with ~10 microns space resolution on ~1 msec time scale. • In respect of spectrum and flux the source is promising for noninvasive human angiography. Thank you!

26. X-ray small animal imaging system at SRF SPring-8 • Designed pulsed LEXG providing in vivo imaging : • # of bunches in a train – 104, 100 laser pulses in a train, • laser pulse energy – 10 mJ, laser train energy – 1 J, • repetition rate – 30 Hz, average laser power 30 W, • # of photons in 0.1 msec flash - 5∙1010. Pulsed operation mode.

27. In Vivo microangiography at SRF SPring-8 Iwasaki et al,“Synchrotron Radiation Coronary Microangiography”,Arteriosclerosis, Thrombosis, and Vascular Biology, 1326 -1333, June 2007 70um Pulsed operation mode.

28. Experiment: resonant shear modes excitation in DKDP crystal v =1.64x105 cm/s d = 0.8cm b a Fig. 1. Shear vibrations of a square plate ((a)observations and (b) calculation). k = 0..9 n(k) = 1 + 2k Fig.2. Pockels cell transmission at the first 4 shear mode resonances. Fig.3. Millisecond lamp pumped picosecond YAG-Nd laser designed for mcs scale pulsations. AM active laser medium; P polarizer;M1, M2 cavity mirrors; M1, M2 optical time delay mirrors; Pr prism; IA iris aperture; MT mirror telescope; DKDP Pockels cell electrooptical crystal; CC feedback control circuit.

29. Discrete Analysis of Picosecond Laser Dynamics a a b Fig.1. Dynamics of the logistic map a – 2-cycle, b – 4-cycle, c – chaotic dynamics. a Fig.3. Dynamics of the map. b c b Fig.4: Chaotic dynamics,  = - 0.5. Fig. 5. Calculated pulsation period T(rmax) over relative feedback sensitivity. The upper curve is an approximation. c Fig.2. Bifurcation diagram of logistic map (1). Fig.6.Bifurcation diagram at =-0.5. Fig.7. Bifurcation diagram (a) and dynamics (b, c).

30. Generation of milliseconds trains of microsecond spaced ps pulses M.Beck et al, Opt. Comm., 190, 317-326, 2001, MBI, Berlin ~20mJ/pulse Quasi CW train of ps pulses (PTO) Another PTO reduces the number of amplifiers. Preshaped train of ps pulses.