Showing papers by "Dino A. Jaroszynski published in 1994"

Two-color free-electron laser operation.

Abstract: We present the first observation of two-color free-electron laser (FEL) operation using a single electron beam, single optical cavity, and a stepped undulator. The undulator is divided into two sections, each having different deflection parameters, ${\mathit{K}}_{1}$ and ${\mathit{K}}_{2}$, which set the resonance wavelengths for FEL oscillation at each of the nonharmonically related wavelengths. Each of the independently tunable optical pulses can have equal power, as high as half of that obtainable in single-wavelength FEL operation using both undulator sections. Presently the two-color FEL operates in the midinfrared spectral region.

CLIO, an infrared free electron laser facility

Abstract: The “CLIO” Free Electron Laser is a tunable infrared laser that is principally dedicated to users. This laser uses a 30–60 MeV relativistic electron beam, provided by a linear accelerator, and an undulator to provide the optical gain needed for the laser process. This facility has been operating since January 1992, producing laser pulses of about 10 MW in 2 ps, with a tunable wavelength range of 2 to 17.5 μm. The average power depends on the repetition rate of laser pulses, and presently reaches about 2 W (at 1 4 of the maximum repetition rate). Four user rooms are available for general experiments using the CLIO laser beam. Three experiments have already succesfully taken place. Study of two photons absorbtion in InSb and InAs as a function of wavelength; infrared microscopy by tunnelling effect, by peaking the evanescent wave of the laser probe on a sample with an optical fiber, for different wavelengths; and surface spectroscopy using the “Sum Frequency Generation” technique, i.e. by mixing the tunable CLIO infrared laser with a synchronized Nd-Yag laser in order to observe the resonance vibration on a surface. This paper presents the general performances of the accelerator, of the laser and describes the principal application experiments which are now in progress.

Bunch length measurements on CLIO

Abstract: The lengths of both electron and laser micropulses have been measured under various conditions. The width of the electron bunches varies between 8 and 16 ps FWHM for standard operation of the linac in our usual 32–50 MeV range. The laser micropulse length varies between 1.5 and 6 ps at 8 μm, depending on the detuning of the optical cavity length. Shorter pulses of subpicosecond duration have been produced by running our linear accelerator in a configuration where the electron bunches acquire a quasi-linear time-energy relationship while travelling on the side, rather than on the crest, of the accelerating high-frequency wave.

Excite-probe FEL (CLIO) study of two-photon-induced carrier dynamics in narrow gap semiconductors

Abstract: In a previous paper measurements were reported of two-photon absorption (TPA) in the narrow gap semiconductors InAs and InSb utilising the mid-infrared tunability of CLIO. An assumption had to be made concerning the lifetime of the excited carriers in order to interpret the results. We have now made a direct measurement of the lifetime of two-photon-induced free holes in InAs and InSb using an excite-probe technique. We have measured the TPA coefficient over the entire range from one-photon to two-photon threshold, showing good agreement with a non-parabolic band model for the process.