Short pulse generation in solid state lasers by a novel passive technique

Includes bibliographical references (page 216).A novel passive Q-switching technique based on self-focusing is studied theoretically and experimentally. In this paper we present results obtained with a simple aberrationless gaussian model that describes the short pulse generation dynamics for different cavity configurations and different nonlinear characteristics of the focusing medium. Experimental results are also presented that are in good agreement with the predictions of the theoretical model. Preliminary results in ultrashort pulse generation are also presented

Thermal patterning of superconducting films

Includes bibliographical references (page 600).The transient shape control of a superconducting high Tc film by selective optical heating has been addressed in this work, using a non-conventional technique that combines the application of a pulsed magnetic field and the optical heating of the superconducting film by a synchronized pulsed laser. A zero field cooled (ZFC) film was partially protected by a mask before exposing it to the laser radiation. The temperature at the illuminated area rises causing very fast local lowering of the vortex pinning force or may even rise above Tc. As a result, flux penetrates completely the heated area and an effective smaller sample remains in a superconducting critical state. Flux penetration is measured with a pick-up coil for different positions of the mask. Results are described within the critical state model for a strip, where the time integrated voltage signal is approximated to the flux difference between the initial ZFC sample and the final critical state of the "new" (cold) ZFC sample

Design of a fluorescence technique using double laser pulse excitation for the measurement of molecular Brownian dynamics

Includes bibliographical references (page 234).A complete analysis of a novel method to evaluate the rotational diffusion time of fluorescent molecules is presented. It is based on the study of the total fluorescence produced after excitation with two consecutive short laser pulses. Expressions for the total fluorescence energy emitted in this case are derived, which would allow the evaluation of the rotational diffusion time. The main advantages of the proposed method are its simple setup, a time resolution only limited by the exciting laser pulsewidth, and the fact that it does not require fast time response detectors

Light collection and wavelength calibration for an extreme ultraviolet diode array spectrograph

Includes bibliographical references.We describe the use of a simple spherical aluminum-coated mirror to image the radiation of a distant XUV-emitting plasma in the slit of a vacuum spectrograph. Calculations to determine the optimum position and curvature radius of the mirror as a function of the divergence of the emitted plasma radiation are described, Efficient light collection by the grazing incidence mirror allows calibration of an intensified diode array used as a detector with a low-pressure (10-4 Torr) dc capillary discharge that does not require a complex differential pumping system.This work was supported by the National Science Foundation Grant No. ECS 8606226. M. C. Marconi was supported by a fellowship from Universidad Nacional de Buenos Aires and Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina

Study of the soft x-ray emission from carbon ions in a capillary discharge

Includes bibliographical references.The soft x-ray emission from plasma produced in polyacetal and polyethylene capillary discharges excited by current pulses 100 ns full-width half-maximum (FWHM), 50 ns risetime, and peak currents up to 60 kA has been studied. Time-resolved spectra show that intense Cᴠɪ line emission dominates in the polyethylene discharges, peaking shortly after the maximum of the current and vanishing before the end of the current pulse. Polyacetal capillary spectra are dominated by Oᴠɪ lines and show weak Cᴠɪ emission. Plasma density and temperature for the polyethylene discharge were derived from the Stark broadening of Cᴠɪ Balmer lines and the relative intensities of Cᴠɪ and Cᴠ lines. A short (5 ns FWHM) pulse of energetic beam electrons was detected in coincidence with the onset of the discharge. The results are discussed in relation to the possibility of obtaining soft x-ray amplification by plasma recombination in a capillary discharge plasma column.This work was supported by the Department of Energy, Advanced Energy Projects Grant DE-F602-91ER12110 and by the National Science Foundation by Grant ECS 9013372. The work of M. C. Marconi was supported by the Universidad Nacional de Buenos Aires and Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina

Reliable passive mode locking with slow Q switching

An electro-optic modulator (EOM) has been added to a passive mode-locked Nd:glass laser in order to slow Q-switch the cavity. This guarantees that the laser will work near threshold even if the gain of the laser medium or the losses change from shot to shot. The losses at the EOM are used as the output coupling. This new configuration allows more reliable operation of the system

Obtención de pulsos de alta potencia en radiación laser por medio de un nuevo método en la conmutación de la cavidad de oscilación

Fil:Marconi, Mario Carlos. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Scanning mechanism based on a programmable liquid crystal display

Includes bibliographical references (pages 112-113).In this work we propose a new robust optoelectronic scanning system for scanning microscopy. The device is based on a programmable liquid crystal television display (LCTV) that acts as a pixel-by-pixel controlled pure phase spatial light modulator. The computer addressed liquid crystal screen allows synthesize different diffractive optical elements at video rates. The phase shifts introduced by these elements make possible a complete control over the position and focusing of the scanning beam

Magnified expansion and compression of subpicosecond pulses from a frequency-doubled Nd:YLF laser

Includes bibliographical references.Pulses from a mode-locked frequency-doubled Nd:YLF laser have been spectrally broadened and subsequently expanded to more than 200 ps and recompressed to 750 fs by grating compressors with magnifying telescopes. The new design magnifies the time delay dispersion to a factor 10 times larger than achievable with standard compressors of similar size. The design of the system and its sensitivity to the variations in the position of its optical components is analyzed. The scheme will allow efficient amplification of subpicosecond pulses in dye amplifiers.This work was supported by N.S.F.-CONICET U.S.A./Argentina Cooperative Science Program under Grant INT 8802563, and by the National Science Foundation under Grants ECS 870507 and ECS 8606226. M. C. Marconi was supported by a Fellowship from the Universidad Nacional de Buenos Aires and Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina