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Ultrafast X-ray Streak Camera Development for High-Resolution Imaging

The objective was to design a camera with 100fs resolution for studying physical processes and correlations. Development milestones showcased improvements in resolution over the years. Factors such as transit time dispersion and electrode geometry were analyzed for enhancing temporal resolution. Various aspects affecting the scanning speed, cable effects, and photoconductive switch behavior were investigated. The calibration setup and modifications like introducing a variable slit and changing the lens geometry were detailed. The camera achieved a resolution of 470fs with a potential for 200fs in the future.

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Ultrafast X-ray Streak Camera Development for High-Resolution Imaging

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  1. Development of an Ultrafast Accumulative X-ray Streak Camera Mahendra Shakya , Jinyuan Liu, Bing Shan And Zenghu Chang J.R.Macdonald Laboratory Kansas State University, KS

  2. OBJECTIVE To Design Camera With Resolution 100fs

  3. Motivation • Study of physical process requires fast detector • Auto correlation and Cross correlation require material with efficient non-linear effect.Not applicable for X-ray • X-ray Streak Camera Provides Intensity, Time and Space information

  4. Streak Camera Convert time into space Dt =Dx/v Dx v Dt Film Mirror Slit

  5. Streak Tube Electrostatic Lens Phosphor Screen Slit1 Slit2 Deflection Plate X-ray Signal CCD MCP Anode Cathode Laser Pulse GaAs Switch

  6. Developments  1975 first demonstration  1990 2ps resolution • 1996 0.5ps resolution in single-shot mode, Z.Chang (Appl.Phys.Lett.69,1(1996) • 2001 0.7 ps in accumulation mode (G.A.Naylor, et al.) by improving laser stability • 2002 0.8 ps (Belzile et al.) by using multiplephotoconductive switches • 2003 Jinyuang Liu 590 fs in accumulation mode Appl. Phys Lett. 82, pp. 20 (2003, )

  7. Factors Affecting Temporal Resolution in Accumulative Mode • Transit Time Dispersion Velocity distribution,Angular distribution • Scanning Speed Dt s= Dx/v x •TimingJitter E V

  8. Anode Collimating slit Cathode Au E Effect of E field on Transit Time Dispersion • High electric field 10.6V/mm 13.75V/mm 176fs 135fs tpsReduced By 23% • Collimating Slit x Reduced 50%

  9. Factors Affecting Temporal Resolution in Accumulative Mode • Transit Time Dispersion Velocity distribution,Angular distribution • Scanning Speed Dt s= Dx/v x •TimingJitter E V

  10. Reducing x by Changing Electrode Geometry x y -/2 re +/2 +/2 ro -/2 re= radius of the electrode r0= radius of the gap The best focused static image width, x = 175 m(25pixels)

  11. Static Image Vb=0V , Vf = 85V, Laser energy = 60 J , 6600 Shots, Exposure time = 6s

  12. Images with re/r0 = 1.9 FWHM, x = 560m

  13. Factors Affecting Temporal Resolution in Accumulative Mode • Transit Time Dispersion Velocity distribution,Angular distribution • Scanning Speed Dt s= Dx/vx •TimingJitter E V

  14. Effect Of Cables and Switch on Scanning Speed +V0 -V0 Es DP arm 1 Rb DF arm 2 Rb RL RL GaAs switch 2GHz cable, t = 90ps, 18GHz cable , t =60 ps

  15. Deflection Plate Output With 18GHz Cables +V0 -V0 Es DP arm 1 Rb Rb DP arm 2 RL RL GaAs switch t1/ 

  16. Factors Affecting Temporal Resolution in Accumulative Mode • Transit Time Dispersion Velocity distribution,Angular distribution • Scanning Speed Dt s= Dx/v x •TimingJitter E V

  17. Photoconductive Switch The pulse amplitude of GaAs switch changes with trigger laser energy

  18. Laser Energy Vs Pulse Amplitude of the Switch

  19. Streak Camera Calibration Setup CCD GaAs STREAK CAMERA STREAK CAMERA 267nm L2 L1 f=150mm f=100mm 800nm ,25 fs

  20. Cathode Voltage Vs Scanning Speed

  21. Bias Voltage Vs Scanning Speed Vf = 85V, Vc=8.5 kV, Laser Energy = 60 J

  22. Cathode Voltage Vs Temporal Resolution Temporal resolution 470fs at –8.5kV Vb=  68.3V, Vf=  85V , Laser Energy = 60J, 6600 shots, Exposure time = 6.6sec

  23. Electron Sweep Speed Vb=  68.5V, Vc= -8.5kV, Vf=  8.5V, Laser Energy = 60J

  24. Time Resolution with Variable Slit Vc= -8.5kV, Vb=  68.3V, Vf=  85V,Exposure time = 6s, 6600 Shots.Laser energy = 60J

  25. Intensity Vs Time at -11KV Cathode Voltage 6600 Shots average sub-picosecond pulse width streak image, Exposition time= 6.6 sec, Vb=  68.3v,Vc=-11kV, Vf=  90 Laser Energy=60J

  26. Modification Made • Introducing variable slit to collimate electron beam • Qudrupolens Geometry. Changed re /r0 from 1.9 to 1.147

  27. Summary • High deflection sensitivity: • 20 cm/kV • Photoconductive Switch: • 60ps rise and fall time • Fast response time: • 120 ps rise and fall time • High scanning speed: • 2c • Current Status • 470fs • Camera Potential • 200fs

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