Status of the SPARC laser and “dazzler” experiments A.Ghigo for SPARC laser group SPARC Review Committee 4-10-2004

Laser requested parameters Requirement Operating Wavelength 260 nm Pulse energy on cathode 500 µJ (Q.E.=10-5) Energy jitter (in UV) 5 % rms Temporal pulse shape Uniform (20% ptp) Transverse pulse shape Pulse rise time (10-90%) < 1 ps Pulse length (Gaussian) 0.5-12 ps Repetition rate 10 Hz Laser-RF jitter < 1ps rms Spot radius on cathode Circular 1 mm SPARC Review Committee 4-10-2004

The laser system consist of the following subsystem:                                       LASER SYSTEM DESCRIPTION   The laser system consist of the following subsystem: a) the mode-locked Ti:Sapphire laser oscillator 100 – 300 femtosecond configuration; central wavelength 800 nm with a bandwidth > 30 nm. b) the oscillator pump must be a diode pumped CW solid state laser at 532 nm (doubled Nd laser). c) the steering optics that permits to introduce the pulse shaper between the oscillator and the amplifiers d) the stretcher system composed by the optics that permit to lengthen the oscillator pulse e) the first Ti:Sapphire regenerative amplifier operating at high repetition rate (kHz) f) the pump of the regenerative amplifier must be a high power solid state laser operating in the green region (doubled Nd laser) with high repetition rate (> 1 kHz) g) the Ti:Sapphire multipass amplifier that provide the final IR energy per pulse h) the pump of the multipass amplifier must be a pulsed solid state laser (doubled Nd laser) operating at 10 Hz l) the compressor system optics that restore the laser pulse-length at the requested value m) the second and third harmonic generation crystals that convert the IR to the UV radiation. n) the synchronization system that permits to lock the timing (frequency and phase) to a stable external reference oscillator with a timing jitter less than 0.5 psec

Laser system schematic layout w 3 y x P u m p T i : S a O s c l t o r g n v f M F x y 3 w _ C d G z Stretcher Compressor UV Pulselength variator

SPARC Laser System schedule 11/06/2003 Technical Specifications ready 27/06/2003 Tender request started (delibera) 26/11/2003 Invitation letter sent to the firm 11/02/2004 Tender request closed (COHERENT) 01/03/2004 Construction started 08/09/2004 Optical table installed (Newport) 01/10/2004 Clean room tests started 11/2004 Complete system test at the factory 12/2004 Laser shipment 2-3/2005 Installation at INFN and final test

“Dazzler” experiments Shaping obtained with single passage in the AO crystal + 30 cm dispersive glass

Best results in Politecnico di Milano experiment Square Pulse at the Pulse shaper exit after the oscillator

Brookhaven experiment DUV-FEL Laser System Amplified Ti:Sa with 10 nm FWHM The laser is use to drive the photocathode and to seed the HG before the undulator The laser is composed by. Tsunami oscillator and related pump Regenerative and 2 multipass amplifiers Two compressor to produce the sub-ps pulse for HGHG and 10 ps for the electron photoemission SPARC Review Committee 4-10-2004

Brookhaven experiment layout Dazzler location

SPARC Review Committee 4-10-2004 Diagnostic Systems Laser beam time and frequency domain diagnostics: ps streak camera for single shot low resolution measurement UV multishot cross-correlator for high resolution (150 fs) SPIDER for phase and amplitude reconstruction usable for pulse < 1 ps spectrometers SPARC Review Committee 4-10-2004

SPARC Review Committee 4-10-2004 Dazzler Test The Dazzler is used in single passage configuration before the amplifier, external dispersion is added by off-balance the stretcher-compressor The experiment is directed toward the production of the flat top pulse after the amplification and UV-conversion. SPARC Review Committee 4-10-2004

Stretched pulse measurement The pulse is 20% flat and the edge are very sharp 350 ps Temporal profile measurements have been made only by streak camera at different position

After Pulse Compressor Also the compressor introduce distortions. For their characterization the amplified was bypassed. The measurement after compression of the “flat” stretched pulse shows not understood changes of the shape.

After Pulse Compressor (After some work) 17 ps Correction

After Pulse Amplification Amplification seems to introduce distortions caused by gain narrowing and because the front edge experience an higher gain Streak camera snapshot of the previous pulse after amplification upstream the compressor

Pulse shape after amplification and compression Last minute result Dazzler set up made with streak camera High resolution spectrometer needed

Next step Use the dazzler to pre-compensate better the distortions generated by the Amplifiers and move for a fine shaping to the UV conversion

Diagnostics needed for final laser test Two high resolution spectrometer (IR – UV) Single shot autocorrelator Energy meters (main laser pulse meas.) Power meters (laser pumps meas.) UV cross-correlator Streak Camera

Optical transfer line status Transfer line channel design almost ready Optical component specs ready for call for offers Linear stages and gimbal mounts to be defined according to the final layout