Schmidt, B.

Paper	Title	Page
MOPCH016	Bunch Compression Monitor	86
	H. Delsim-Hashemi, J. Rossbach, P. Schmüser Uni HH, Hamburg O. Grimm, H. Schlarb, B. Schmidt DESY, Hamburg A.F.G. van der Meer FOM Rijnhuizen, Nieuwegein
	An accelerated bunch of electrons radiates coherently at wavelengths longer than or comparable to the bunch length. The first generation Bunch Compression Monitor (BCM) that is installed at the VUV-FEL applies this principle by measuring the total radiation intensity. For a better control on the degree of the compression, the radiated intensity in different bandwidth can be used. Dependent on the changes in the structure of the bunch, its radiation spectrum changes correspondingly. A new generation BCM uses wavelength dependent diffracting devices and multi-channel sensors to measure the signal in different wavelength channels simultaneously. This paper describes the construction of the first prototypes and experimental results in different short wavelength bands measured at the linac of the VUV-FEL at DESY, Hamburg.
TUPCH024	Comparative Study of Bunch Length and Arrival Time Measurements at FLASH	1049
	H. Schlarb, A. Azima, S. Düsterer, M. Huening, E.-A. Knabbe, M. Roehrs, R. Rybnikov, B. Schmidt, B. Steffen DESY, Hamburg M.C. Ross SLAC, Menlo Park, California P. Schmüser, A. Winter Uni HH, Hamburg
	Diagnostic devices to precisely measure the longitudinal electron beam profile and the bunch arrival time require elaborate new instrumentation techniques. At the VUV-FEL, two entirely different methods are used. The bunch profile can be determined with high precision by a transverse deflecting RF structure. The method is disruptive and does not allow to monitor multiple bunches in a macro-pulse train. Therefore, it is augmented by two non-disruptive electro-optical devices, called EO and TEO. The EO setup uses a dedicated diagnostic laser synchronized to the machine RF. The longitudinal electron beam profile is encoded in the intensity profile of a chirped laser pulse and analyzed by looking at the spectral composition of the pulse. The second setup, TEO, utilizes the TiSa-based laser system used for pump-probe experiments. Here, the temporal electron shape is encoded into a spatial dimension of laser pulse by an intersection angle between the laser and the electron beam at the EO-crystal. In this paper, we present a comparative study of bunch length and arrival time measurements performed simultaneously with all three experimental techniques.
TUPCH026	Single Shot Longitudinal Bunch Profile Measurements at FLASH using Electro-optic Techniques	1055
	B. Steffen, E.-A. Knabbe, B. Schmidt DESY, Hamburg G. Berden, A.F.G. van der Meer FOM Rijnhuizen, Nieuwegein W.A. Gillespie, P.J. Phillips University of Dundee, Nethergate, Dundee, Scotland S.P. Jamison, A. MacLeod UAD, Dundee P. Schmüser Uni HH, Hamburg
	For the high-gain operation of a SASE FEL, extremly short electron bunches are essential to generate sufficiently high peak currents. At the superconducting linac of the VUV-FEL at DESY, we have installed an electro-optic experiment with temporal decoding and spectral decoding to probe the time structure of the electric field of single sub 200fs e-bunches. In this technique, the field-induced birefringence in an electro-optic crystal is encoded on a chirped ps laser pulse. The longitudinal electric field profile of the electron bunch is then obtained from the encoded optical pulse by a single-shot cross correlation with a 30 fs laser pulse using a second-harmonic crystal (temporal decoding) or by a single-shot measurement of its spectrum (spectral decoding). In the temporal decoding measurements an electro-optic signal of 230fs FWHM was observed, and is limited by the material properties of the particular electro-optic crystal used. Bunch profile and time jitter measurements were obtained simultaneously with VUV SASE operation.
TUPCH027	Time Resolved Single-shot Measurements of Transition Radiation at the THz Beamline of FLASH using Electro-optic Spectral Decoding	1058
	B. Steffen, E.-A. Knabbe, B. Schmidt DESY, Hamburg G. Berden, A.F.G. van der Meer FOM Rijnhuizen, Nieuwegein W.A. Gillespie, P.J. Phillips University of Dundee, Nethergate, Dundee, Scotland S.P. Jamison, A. MacLeod UAD, Dundee P. Schmüser Uni HH, Hamburg
	Single-shot electro-optic detection was used to measure the temporal profile of coherent transition radiation (CTR) pulses at the VUV-FEL at DESY. The CTR was generated from single bunches kicked to an off-axis screen, with the radiation transported through a 20m long transfer line imaging the CTR from a radiation screen to an experimental station outside the accelerator tunnel. Bipolar pulses with a FWHM less than 1ps have been measured and are consistent with simulations of the propagation of radiation through the transfer line.
TUPCH028	Layout of the Optical Synchronization System for FLASH	1061
	A. Winter, P. Schmüser, A. Winter Uni HH, Hamburg F. Loehl, F. Ludwig, H. Schlarb, B. Schmidt DESY, Hamburg
	The present RF synchronization system of the VUV-FEL can typically stabilize the arrival time of the electron bunches at the undulator to about 200 fs on a timescale of minutes and to several picoseconds on a timescale of hours. To improve the machine stability and to ensure optimal performance for the VUV-FEL user facility, a new ultra-precise timing system is mandatory. The optical synchronization system under construction will satisfy three goals: Firstly, it provides a local oscillator frequency with the same stability as the existing low-level RF regulation, secondly, it can synchronize the experimental lasers of the FEL users with a precision in the order of 30 fs, thirdly, it provides an ultra-stable reference for beam arrival time measurements and enables a feedback on the electron beam to compensate residual drifts and timing jitter. The optical synchronization system is based on an optical pulse train from a mode-locked laser with a highly stabilized repetition rate. This paper describes the proposed layout of the optical synchronization system, the integration into the machine layout and the diagnostic experiments to monitor the performance of the system.
THOBFI01	A Sub 100 fs Electron Bunch Arrival-time Monitor System for FLASH	2781
	F. Loehl, K.E. Hacker, F. Ludwig, H. Schlarb, B. Schmidt DESY, Hamburg A. Winter Uni HH, Hamburg
	The stability of free-electron lasers and experiments carried out in pump-probe configurations depends sensitively on precise synchronization between the photo-injector laser, low-level RF-systems, probe lasers, and other components in the FEL. A measurement of the jitter in the arrival-time of the electron bunch with respect to the clock signal of a master oscillator is, therefore, of special importance. For this task, we propose an arrival-time monitor based on a beam pick-up with more than 10GHz bandwidth which permits measurements in the sub 100 fs regime. The RF-signal from the beam pick-up is sampled by an ultra-short laser pulse using a broad-band electro-optical modulator. The modulator converts the electron bunch arrival-time jitter into an amplitude modulation of the laser pulse. This modulation is detected by a photo detector and sampled by a fast ADC. By directly using the laser pulses from the master laser oscillator of the machine, any additional timing jitter is avoided. In this paper we present the layout of the system and first experimental results.
	Transparencies