Experimental validation of model for pulsed laser-induced subsurface modifications in Si

Wafers are traditionally diced with diamond saw blades. Saw dicing technology has a number of limitations, especially concerning the dicing of thin wafers. Moreover, the use of fluids and the gen-eration of debris can damage fragile components such as micro electro-mechanical systems. Laser ablation dicing is better suited for thin wafers, but is also not a clean process. An alternative dicing method is subsurface laser dicing. This technology is based on the production of laser-induced sub-surface modifications inside the wafer. These modifications weaken the material, such that the wafer separates along the planes with laser modifications when applying an external force. To find the right laser conditions to produce subsurface modifications in silicon, and to enhance the understand-ing of the underlying physics, a numerical model has previously been developed. To validate this model, the current work compares simulation results with experimental data obtained by focusing nano- and picosecond pulses inside silicon wafers. A fairly good agreement between experimental and numerical results was obtaine

Direct Measurement of the Shape of Short Electron Bunches

We describe a technique to measure the longitudinal density distribution of electron bunches with sub-picosecond resolution by means of electro-optic sampling of the Coulomb field of the electrons

FEL diagnostics and user control

The most recent upgrades and improvements to the free-electron laser (FEL) facility FELIX are presented. Special attention is paid to the improved beam-handling and diagnostic station. In this evacuated beam station a device is implemented that is capable of selecting single micropulses with measured efficiencies of more than 50% over the whole wavelength range of FELIX (5-110 mu m). Furthermore, the broadband autocorrelator for micropulse length measurements and the planned continuous polarization rotator based on reflective optics are discussed. Recent additions to the ancillary equipment available to FEL users are presented briefly. The most important ones are the mirror-dispersion-controlled 10-fs Ti:sapphire laser and the 40-T magnet. (C) 1998 Elsevier Science B.V. All rights reserved

Experimental Indications for Non-Gaussian Transverse-Modes in the Hole-Coupled, Short-Pulse Free-Electron Lasers of Felix

The radial structure of intra-cavity light pulses is considered in the hole-coupled free-electron laser (FEL) oscillators of the Dutch FEL facility, FELIX. In a previous numerical study, it was shown that the radial profile can vary significantly over the light pulse, in particular when the electron pulses are short with respect to the slippage length. In this paper experimental indications are presented for the predicted transverse profile of the radiation. The decay of the power coupled out through the hole has been measured, after the electron beam was switched off, for the two different resonators employed in FELIX. These resonators differ in cavity length, mirror curvature and aperture radius, and in the width of the vacuum tube inside the undulator. The decay rate of the extracted radiation is interpreted according to the calculated intra-cavity mode structure from ELIXER. This simulation code describes the time-dependent radial profile in terms of a finite number of Gauss-Laguerre functions. Two extreme cases are discussed in further detail, one in which edge losses are large and one in which they are small

Shedding new light on thermionic electron emission of fullerenes

Contains fulltext : 98985.pdf (publisher's version ) (Open Access

A far-infrared broadband (8.5-37 mu m) autocorrelator with sub-picosecond time resolution based on cadmium telluride

A background-free autocorrelator has been developed for measuring the duration of far-infrared laser pulses in the spectral range from 8.5 to 37 mum by using an 840-mum-long wedged cadmium telluride crystal as the second-harmonic generator. Typical intensity second-harmonic autocorrelation traces are given for the wavelengths of 19.7 and 37 mum, indicating FWHM pulse duration of 0.90 and 1.5 ps respectively. An interferometric autocorrelation trace at 18.2 mum has been measured for the first time, and the distortion of autocorrelation traces due to the absorption and re-emission of ambient water vapor is shown at 28 mum. (C) 2001 Elsevier Science BN. All rights reserved

Cavity ring down spectroscopy with a free-electron laser

Item does not contain fulltex

Observation of superradiance in a short-pulse fel oscillator

Superradiance has been experimentally studied, in a short-pulse free-electron laser (FEL) oscillator. Superradiance is the optimal way of extracting optical radiation from an FEL and can be characterised by the following scale laws: peak optical power P, scales as the square of electron charge, Q, (P, &unknown; Q2); the optical pulse duration, z, scales as the inverse of the square root of the charge, (z &unknown; 1/Q); the efficiency, , scales as the inverse of optical pulse length ( &unknown; 1/z &unknown; Q), which also implies that the relative spectral brightness defined by /(/) remains constant and close to 0.86. To characterise the properties of the superradiant emission, we have measured the efficiency, optical pulse energy, pulse duration and spectral width as functions of electron beam current and cavity loss for the optimum cavity length detuning. The efficiency has been deduced from measurements of electron beam energy spectra. The optical pulse duration has been determined from second-order autocorrelation measurements and the optical spectra determined using a grating spectrometer. We show that the superradiance in the oscillator has properties similar to that in a high-gain amplifier and discuss the links with spikes created by synchrotron instabilities