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30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Optical sampling system for detailed measurement of the longitudinal pulse.

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Presentation on theme: "30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Optical sampling system for detailed measurement of the longitudinal pulse."— Presentation transcript:

1 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Optical sampling system for detailed measurement of the longitudinal pulse shape Ingo Will, Guido Klemz Max Born Institute Berlin 100 ps (10mm glass plate)

2 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Present status at PITZ: Pulse shape is measured using a synchroscan streak camera Present limits: Streak camera signal is noisyStreak camera signal is noisy Resolution limited:Resolution limited: Green light: to 2...4 psGreen light: to 2...4 ps UV light: to 3…5 psUV light: to 3…5 ps Measurement is sensitive to illumination of the cathodeMeasurement is sensitive to illumination of the cathode space-charge effects in the streak tube: pulse broadening to 60 psspace-charge effects in the streak tube: pulse broadening to 60 ps no direct measurement for IRno direct measurement for IR modification of the pulse shape in the amplifier chain cannot be investigatedmodification of the pulse shape in the amplifier chain cannot be investigated laser #2 time Measurement: Nov 03, 2003 resolution limited to 3..4 ps strong intensity noise of the streak camera

3 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Pre-compensation of changes of the pulse shape during amplification and conversion to the UV IR = 1.047  m green = 0.524  m UV = 0.262  m

4 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Two-stage regenerative amplifier concept n Thermal lens in the power regen leads to a drop of the intensity to 50% during 2000 pulses n The two- or three-stage regen concept may enable us to apply advanced amplifier techniques (i.e. thin-disk amplifiers) First regen Second regen E micro = 15  J E micro = 3  J 2ms (2000 pulses) Yb:KGW oscillator Yb:YAG regen Yb:YAG power regen DST shaper Drop due to thermal lensing First regen Second regen Compensation of the drop by the drive current of the pump diodes, but the „pumping“ of the beam diamter remains! 2ms (2000 pulses) E micro = 15  J E micro = 3  J

5 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Formation of flat-top laser pulses output pulses recorded with a streak camera: n Flat-top laser pulses generate electron bunches with a flat-top shape in z-direction -> improved brightness of the electron beam-> improved brightness of the electron beam

6 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Simple DST shaper forming flat-top laser pulses output pulses recorded with a streak camera: n Flat-top laser pulses generate electron bunches with a flat-top shape in z-direction -> improved brightness of the electron beam-> improved brightness of the electron beam

7 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Amplification of flat-top pulses from an Yb:YAG oscillator Record of flat-top pulses with a synchroscan streak camera (Optronis, ~3...4 ps resolution) at 515 nm wavelength n Parameters of the pulses shown: length of the train: 1.5 ms (1500 pulses)length of the train: 1.5 ms (1500 pulses) Energy in the train: 27 mJEnergy in the train: 27 mJ Energy per micropulse: 18  J (at 1030 nm)Energy per micropulse: 18  J (at 1030 nm) Streak camera measurement taken with SHG (at 515 nm)Streak camera measurement taken with SHG (at 515 nm) n Energy is ~ 4…5 times smaller than in the present Nd:YLF phothocathode laser n Increasing this energy is a major challenge to the laser designer 100 ps (10mm glass plate)

8 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Requirements for a system measuring the pulse shape Further progress in pulse shaping requires a measurement system with the following parameters: n Temporal resolution: better 1 ps n Suitable for IR, green and UV light n Clean signal, reliable measurement especially for: the edgesthe edges the flatness of the pulsethe flatness of the pulse Question: How to build a system that displays the pulse shape in a real- time manner ? (complete measurement during each laser shot)

9 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Different beam shapes depending on the alignment of the shaper These images are taken with 5 Hz repetition rate and displayed on an oscilloscope in a real-time manner

10 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system How does the optical sampling system work n Every sampling measurement system requires 1. periodic signals 2. a very fast gate 3. Synchronization of the gate to the signal

11 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Sampling measurement systems n Example of a sampling measurement device: Commercial RF sampling oscilloscopes electrical switch based on very fast switching diodeselectrical switch based on very fast switching diodes gating time (=resolution) reached with of today’s sampling oscilloscopes:  ~ 15 psgating time (=resolution) reached with of today’s sampling oscilloscopes:  ~ 15 ps n Optical sampling system: utilizes periodicity of the micropulses in the train (requires > 100 micopulses)utilizes periodicity of the micropulses in the train (requires > 100 micopulses) Fast optical gate: mixing with short laser pulsesFast optical gate: mixing with short laser pulses Gating time (=resolution) determined by the duration of the pulses from the laser oscillator of the sampling system (at present:  = 0.5…0.6 ps)Gating time (=resolution) determined by the duration of the pulses from the laser oscillator of the sampling system (at present:  = 0.5…0.6 ps) ~ 12 ps FWHM

12 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Sampling system presently used to measure the pulse shape in the IR ~ 12 ps FWHM

13 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Stable synchronisation during the scan requires an embedded C++ state machine

14 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Shortest pulses and bandwidth of this amplifier combination E micro = 2x7  J E micro = 3  J Yb:KGW oscillator Yb:YAG regen Yb:YAG power regen E micro = 2x0.3  J 12ps 2ps n Output pulses of the KGW oscillator:  = 0.5 ps n Output pulses of the regen combination:  = 1.8 ps n Can pulses of this duration efficiently be transferred to the UV (forth harmonics, = 258 nm) ?

15 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Typical pulse shapes measured with the optical sampling system n Present status: n Sampling system operational in the IR (1030 nm) n work is ongoing to extend the measurement to the UV Gaussian pulseflat-top pulse non-Gaussian pulse 6 ps25 ps ~ 14 ps FWHM edges < 2 ps

16 30. Nov. 2006 I.Will, G. Klemz, Max Born Institute: Optical sampling system Summary n An optical sampling system is being developed at the MBI displays the shape of ps pulses on a standard oscilloscope in a real-time mannerdisplays the shape of ps pulses on a standard oscilloscope in a real-time manner Based on cross correlation between the pulses to be measured and the femtosecond pulses from a KGW oscillatorBased on cross correlation between the pulses to be measured and the femtosecond pulses from a KGW oscillator Temporal resolution: 0.5 psTemporal resolution: 0.5 ps Linearity in time: ~ 10%Linearity in time: ~ 10% n The system utilizes the periodicity of the pulses of the photocathode lasers used at FLASH and PITZ n Work is ongoing extend the measurement range to the UV


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