FLASH Experiments with Photons High intensity laser light in the VUV spectral region Harald Redlin; HASYLAB

What is FLASH ? Free Electron Laser (FEL) generating short light pulses in the spectral region 13 … 47 nm Second phase of development on the way to an X-ray FEL User facility and playground for accelerator improvement at the same time First lasing on / start of user operation: August 2005 Outline of the lecture 1.Generation of the VUV-photons 2.Properties of the VUV-laser 3.Examples for first experiments 4.Optical pump-probe laser and experiments using it "F"ree-Elektron-"LAS"er in "H"amburg

Principle of Free Electron Lasers

Electron accelerator and undulator Gun laser: 10 ps pulses, 262 nm 5 supraconducting accelerator modules Synchronization between Gun-laser and RF in accelerator moduls with ps precision

Electron accelerator and undulator

Characterization of the VUV-photons Multibunch SASE signal (µJ) recorded with MCP detector max. average single Wavelength13 … 40 nm Average energy per pulse48 32 nm Maximum energy per pulse nm Radiation pulse duration25 fs Peak power (from average) nm Spectral width (FWHM)0.8 % Angular divergence (FWHM)160 µrad Peak brilliance 0.3*10 28 ph/s/mrad 2 /mm 2 /(o.1%bw.) 3 mm spot size 18.5 m distance  high degree of coherence A gold mesh (0.25 mm ptch) in front of the Ce:YAG screen is used as intensity detetor Energy calibrated with gas detector

Spatial coherence horizontal vertical Double-slit diffraction

Angular divergence

Spectrum

Experimental hall

Beam distribution into the experimental hall

Examples of first experiments Ablation/ damage threshold of materials Cluster experiments Atomic excitations – spectroscopy, non- linear effects User operation startet in August 2005

Ablation experiment CCD VUV-beam UHV-chamber sample probe-beam: Courtesy of K. Sokolowski-Tinten

Ablation in slow-motion

Single-pulse diffraction imaging Short wavelength is necessary, i. e. X-rays Problem: T he first X-ray photons will destroy the sample -> data collection with low intensity source is not possible Alternative method: Use diffraction data with one high intensity X-ray pulse Question: Is it possible to obtain data before coulomb explosion and thermal destruction of the sample ? Task: High resolution imaging of single molecules or small clusters

Single-pulse diffraction imaging Sample made by etching a pattern into a Si 3 N 4 film Diffraction pattern from 1 st VUV pulse Diffraction pattern from 2 nd VUV pulse Image recon- structed from diffraction pattern [Source: H. Chapman, J. Hajdu in “XFEL Technical Design Report”, DESY ]

Pump-probe experiments Optical Laser : NIR = 800 nm,  = 150 fs, E = 25 µJ VIS = 523 nm,  = 10 ps, E = 250 µJ

Synchronization measurement with Streak-camera

Pump-probe experiments Energy spectrum of photo- electrons without optical laser Sideband generated at simultaneous action of VUV- and NIR photons = 32 nm = 800 nm

Synchronization measurement with electrooptical sampling