Steffen, B.

Paper	Title	Page
TUYPA01	Femtosecond Bunch Length Measurements	915
	S.P. Jamison CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire G. Berden FOM Rijnhuizen, Nieuwegein W.A. Gillespie, P.J. Phillips University of Dundee, Nethergate, Dundee, Scotland A. MacLeod UAD, Dundee B. Steffen DESY, Hamburg
	The measurement of ultrashort longitudinal bunch profiles is of growing importance to accelerator development and operation. With requirements of ~10fs time resolution, and a desire for non-destructive and real time diagnostics, the challenges for diagnostic development are significant. Alongside more established transverse deflecting cavity and CTR measurement techniques, new approaches arriving from the field of ultrafast lasers offer significant potential; Ultrafast electro-optic detection has now been demonstrated on several accelerators, and in many distinct forms, although challenges remain in getting to the desired time resolution. Proposed schemes combining ultrafast laser diagnostics with FEL interactions, such as the "optical replica" scheme also have considerable potential. Here, an overview of the current status of femtosecond scale longitudinal profile diagnostics will be given, together with an outlook to the future expectations.
	Transparencies
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.
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.