1 / 27

Photocathode lasers generating long trains of flat-top pulses

Photocathode lasers generating long trains of flat-top pulses. Ingo Will, Guido Klemz Max Born Institute Berlin. 1 m s. 100 ps (10mm glass plate). 800 m s. Optical sampling system for high-resolution measurement of the longitudinal pulse shape. Ingo Will, Guido Klemz

arty
Download Presentation

Photocathode lasers generating long trains of flat-top pulses

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Photocathode lasers generating long trainsof flat-top pulses Ingo Will, Guido Klemz Max Born Institute Berlin 1 ms 100 ps (10mm glass plate) 800 ms I.Will et al., Max Born Institute: Long trains of flat-top laser pulses

  2. Optical sampling system for high-resolution measurement of the longitudinal pulse shape Ingo Will, Guido Klemz Max Born Institute Berlin 100 ps (10mm glass plate) I.Will et al., Max Born Institute: Long trains of flat-top laser pulses

  3. The desired pulse trains and pulse energy(superconducting linac, Cs2Te photocathode) 1 ms Desired parameters (according to the requirements specified by DESY): • Spacing of the pulses: 1 ms • In future: 0.2 ms = 5 MHz (XFEL) and 0.11 ms = 9 MHz (option for FLASH) • Duration of the pulse train: at least 800 ms, variable • Very reliable synchronization • Rectangular envelope of the pulse trains • Energy: • > 100 mJ in the IR (I.e. l = 1047 nm) • corresponds to >100 W power during the pulse train • 15 mJ in the UV (I.e. l = 262 nm) 800 ms

  4. Desired pulse shape • Desired parameters of the micropulses • Wavelength: UV (262 nm) • Edges: < 2 ps (UV) • Noise in the flat-top region: < 10…20 % • Pulse duration t ~ 20 ps • Completely remote-controlled laser system • Very reliable synchronization 20 ps < 2 ps < 2 ps

  5. First completely diode-pumped pulse-train laser operational at PITZ since April 2005 Conclusion: The duration of the train in the amplifiers must be much larger (>1.5 ms) than the length of the output train

  6. Pre-compensation of changes of the pulse shape during amplification and conversion to the UV IR l = 1.047 mm green l = 0.524 mm UV l = 0.262 mm

  7. The MBI setup of a generator of long flat-top pulse trains for the superconducting linac photo- photo- photo- diode diode diode #1 #2 #3 output pulses booster pulse modelocked preamplifier amplifier shaper oscillator wavelength auxiliary main conversion pulse picker pulse picker IR -> UV 100 ps 100 ps

  8. MBI setup of a generator of long flat-top pulse trains for the superconducting linac • Effect of all components of the laser on the micropulsesshould be constant for a duration of 800 ms • Components of the laser should work with 1 MHz rep. rate during the train • High average power during the train of the final amplifiers: Ptrain > 100 W photo- photo- photo- diode diode diode #1 #2 #3 output pulses booster pulse modelocked preamplifier amplifier shaper oscillator wavelength auxiliary main conversion pulse picker pulse picker IR -> UV

  9. Selected pulse shaping techniques: suitability for single pulses and pulse trains

  10. Selected pulse shaping techniques/effects: suitability for single pulses and pulse trains UV output pulses

  11. Simple DST shaper forming flat-top laser pulses • Flat-top laser pulses • generate electron bunches with a flat-top shape in z-direction • -> improved brightness of the electron beam output pulses recorded with a streak camera:

  12. Simple DST shaper forming flat-top laser pulses • Flat-top laser pulses • generate electron bunches with a flat-top shape in z-direction • -> improved brightness of the electron beam output pulses recorded with a streak camera:

  13. Amplification of flat-top pulses from an Yb:YAG oscillator 100 ps (10mm glass plate) • Parameters of the pulses shown: • length of the train: 1.5 ms (1500 pulses) • Energy in the train: 27 mJ • Energy per micropulse: 18 mJ (at 1030 nm) • Streak camera measurement taken with SHG (at 515 nm) • Energy is ~ 4…5 times smaller than in the present Nd:YLF phothocathode laser • Increasing this energy is a major challenge to the laser designer Record of flat-top pulses with a synchroscan streak camera (Optronis, ~3...4 ps resolution) at 515 nm wavelength

  14. The MBI setup of a generator of long flat-top pulse trains for the superconducting linac photo- photo- photo- diode diode diode #1 #2 #3 output pulses booster pulse modelocked preamplifier amplifier shaper oscillator wavelength auxiliary main conversion pulse picker pulse picker IR -> UV 100 ps 100 ps

  15. Some amplification techniques: suitability for single pulses and pulse trains

  16. Part 2: OPCPA stage generating femtosecond pulses • OPCPA: Optical Parametric Chirped-Pulse amplification • Generates femtosecond pulses t 150 fs FWHM • pulse energy available at present : Emicro = 100 mJ (before compressor) Emicro = 50 mJ (behind compressor) • Available wavelength: • l = 790…830 nm • on request: l = 395…415 nm output pulse train which contains 700 micropulses

  17. Scheme of the Pump-Probe laser Pump laser OPCPA stage I.Will et al., Max Born Institute: Long trains of flat-top laser pulses

  18. 1ms (1000 pulses) 20 ms Regenerative amplifiers can be made to work at 1 MHz repetition rate • Specialty in burst mode:Each micropulse can extract only a small fraction (~ 0.2%) of the stored energy • Low stability (2% fluctuation during the train) • Reduced efficiency (~50%) in comparison to single pulses • Failure in the trigger will damage the amplifier • sophisticated software solution, (present DOOCS not save) • NL limiter • Fast repair technology Pulse traveling in the resonator Output pulses 50 ns

  19. Emicro = 3 mJ First regen Compensation of the drop by the drive current of the pump diodes, but the „pumping“ of the beam diamter remains! Emicro = 15 mJ Second regen 2ms (2000 pulses) Two-stage regenerative amplifier concept • Thermal lens in the power regen leads to a drop of the intensity to 50% during 2000 pulses • The two- or three-stage regen concept may enable us to apply advanced amplifier techniques (i.e. thin-disk amplifiers) Yb:KGW oscillator Yb:YAG regen Emicro = 3 mJ First regen DST shaper Drop due to thermal lensing Yb:YAG power regen Emicro = 15 mJ Second regen 2ms (2000 pulses)

  20. Amplification of flat-top pulses from an Yb:YAG oscillator 100 ps (10mm glass plate) • Parameters of the pulses shown: • length of the train: 1.5 ms (1500 pulses) • Energy in the train: 27 mJ • Energy per micropulse: 18 mJ (at 1030 nm) • Streak camera measurement taken with SHG (at 515 nm) • Energy is ~ 4…5 times smaller than in the present Nd:YLF phothocathode laser • Increasing this energy is a major challenge to the laser designer Record of flat-top pulses with a synchroscan streak camera (Optronis, ~3...4 ps resolution) at 515 nm wavelength

  21. Without compensationby pump current with compensationby pump current 5 ms(5000 pulses) 5 ms(5000 pulses) Amplification of long pulse trains for the cold linac by an Yb:YAG booster • Energy per micropulse: ~ 15 mJ • Amplification (two stages): G = 5...8 • Stable pulse train: control of the ramp of the current of the pump diodes • Stable beam diameter: beam-shaping aperture at the output • Can the beam-shaping aperture in the beamline play this role? • Technology for lossless stabilisation of the beam diameter: fast deformable mirror Emicro = 3 mJ Emicro = 15 mJ

  22. Shortest pulses and bandwidth of this amplifier combination Emicro = 3 mJ 2ps • Output pulses of the KGW oscillator: t = 0.5 ps • Output pulses of the regen combination: t = 1.8 ps • Can pulses of this duration efficiently be transferred to the UV(forth harmonics, l = 258 nm) ? Yb:KGW oscillator Yb:YAG regen d = 1.2mm 12ps Emicro = 2x0.1 mJ Yb:YAG power regen Emicro = 2x7 mJ

  23. Shortest pulses and bandwidth of this amplifier combination Emicro = 3 mJ • Output pulses of the KGW oscillator: t = 0.5 ps • Output pulses of the regen combination: t = 1.8 ps • Can pulses of this duration efficiently be transferred to the UV(forth harmonics, l = 258 nm) ? Yb:KGW oscillator 2ps Yb:YAG regen 12ps Emicro = 2x0.3 mJ Yb:YAG power regen Emicro = 2x7 mJ

  24. Broadband pulse: UV output pulse from Yb:KGW laser - sharp edges - sharp edges - E beam m - E > 20 J micro micro = 20 - stop l l - = 260 nm m J =1038 nm to photocathode BBO crystal beam stop Narrowband pulse from Nd:YLF laser - slow edges J m = 100 micro - E = 349 nm l - Two-channel mixing scheme: reduced energy requirements to the broadband laser amplifier • 75% of the total laser energy delivered by the Nd:YLF long-pulse system • only 25% need to be delivered by broadband channel

  25. Pre-shaping the beam of the photocathode laser may significantly reduce losses in the beamline present scheme pre-shapingby an aspherical Lens pair

  26. Summary: Long trains of flat-top laser pulses for the superconducting linac • Pulse shaping techniques: Only minor limitations • Most linear pulse-shaping techniques (gratings, filters etc) work for long trains • Techniques based on travelling acoustic waves (i.e. DAZZLER) cannot be used • Nonlinear techniques: limited duration of the pulse train (100...500 micropules) (only for nonlinear techniques using bulk materials) • Amplifiers: • Optical-parametric amplifiers (OPA): work without restrictions, but large pump laser required • For laser amplifiers: The broadband laser materials require regenerative amplifiers in the first stages. These regens can work at 1 MHz for Yb:YAG, Yb:KGW: • With somewhat reduced stability and with slightly less less efficiency (~ 50%) than for single pulses Reason: low saturation during each micropulse (0.2% energy extraction per pulse) • Linear power amplifiers: work well with pulse trains • Some problems arise from the thermal lens, that drifts during the train Solution: Dynamic correction with fast deformable mirrors • Ti:Saphire: No solutions for long, intense pulse trains available • We have made the correct choice for the laser material: Diode-pumped Yb:KGW and Yb:YAG instead of Ti:Saphire

  27. Amplification of flat-top pulses from an Yb:YAG oscillator 100 ps (10mm glass plate) • Parameters of the pulses shown: • length of the train: 1.5 ms (1500 pulses) • Energy in the train: 27 mJ • Energy per micropulse: 18 mJ (at 1030 nm) • Streak camera measurement taken with SHG (at 515 nm) • Energy is ~ 4…5 times smaller than in the present Nd:YLF phothocathode laser • Increasing this energy is a major challenge to the laser designer Record of flat-top pulses with a synchroscan streak camera (Optronis, ~3...4 ps resolution) at 515 nm wavelength

More Related