Generation of broadband VUV light using third-order cascaded processes

Includes bibliographical references (pages 013601-4).We report the first demonstration of broadband VUV light generation through cascaded nonlinear wave mixing in a gas. Using a hollow-fiber geometry to achieve broad-bandwidth phase-matching, frequency conversion of ultrashort-pulse Ti:sapphire laser pulses from the visible into the deep UV around 200 and160 nm is achieved. A new type of quasi-phase-matching is also observed in the VUV for the first time. Conversion using cascaded processes exhibits higher efficiencies, shorter pulse durations, and broader bandwidths than other schemes for generating light in the deep UV, and will enable many applications in science and technology

Generation of broadband VUV light using third-order cascaded processes

Includes bibliographical references (pages 013601-4).We report the first demonstration of broadband VUV light generation through cascaded nonlinear wave mixing in a gas. Using a hollow-fiber geometry to achieve broad-bandwidth phase-matching, frequency conversion of ultrashort-pulse Ti:sapphire laser pulses from the visible into the deep UV around 200 and160 nm is achieved. A new type of quasi-phase-matching is also observed in the VUV for the first time. Conversion using cascaded processes exhibits higher efficiencies, shorter pulse durations, and broader bandwidths than other schemes for generating light in the deep UV, and will enable many applications in science and technology

Shaped-pulse optimisation of coherent soft-x-rays

High-harmonic generation is one of the most extreme nonlinear-optical processes observed to date. By focusing an intense laser pulse into a gas, the light-atom interaction that occurs during the process of ionising the atoms results in the generation of harmonics of the driving laser frequency, that extend up to order ~300 (corresponding to photon energies from 4 to >500eV). Because this technique is simple to implement and generates coherent, laser-like, soft-x-ray beams, it is currently being developed for applications in science and technology including probing of dynamics in chemical and materials systems and for imaging. In this work we demonstrate that by carefully controlling the shape of intense light pulses of 6-8 optical cycles, we can control the interaction of light with an atom as it is being ionised, in a way that improves the efficiency of x-ray generation by an order of magnitude. Furthermore, we demonstrate that it is possible to control the spectral characteristics of the emitted radiation and to channel the interaction between different-order nonlinear processes. The result is an increased utility of harmonic generation as a light source, as well as the first demonstration of optical pulse-shaping techniques to control high-order nonlinear processes.Comment: 16 pages, 3 figure

Hyper-Rayleigh scattering with picosecond pulse trains

We propose a method for measuring hyper-Rayleigh scattering employing pulse trains produced by a Q-switched and mode-locked Nd:YAG laser. The use of the entire pulse train under the Q-switch envelope avoids the need of any device to scan the irradiance, as is usually done with nanosecond and femtosecond single-pulse lasers. To verify the feasibility of the technique, we performed measurements in different solutions of para-nitroaniline and compared the results with those obtained with nanosecond pulses. In both cases, the agreement with the hyperpolarizability values reported in the literature is about the same, but the measurements carried out with pulse trains are at least 20 times faster. Besides the advantage of acquisition speed, the use of pulse trains also allows the instantaneous inspection of slow luminescence contributions arising from multiphoton absorption. (C) 2008 Optical Society of America

Coherent femtosecond VUV generation via Guided Wave Phase Matched Parametric Generation

NRC publication: Ye

Control of Two-Photon Absorption in Organic Compounds by Pulse Shaping: Spectral Dependence

In this work, we investigate the control of the two-photon absorption process of a series of organic compounds via spectral phase modulation of the excitation pulse. We analyzed the effect of the pulse central wavelength on the control of the two-photon absorption process for each compound. Depending on the molecules` two-photon absorption position relative to the excitation pulse wavelength, different levels of coherent control were observed. By simulating the two-photon transition probability in molecular systems, taking into account the band structure and its positions, we could explain the experimental results trends. We observed that the intrapulse coherent interference plays an important role in the nonlinear process control besides just the pulse intensity modulation.FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq (Conselho Nacional de Desenvolvimento Cientifico)

ATOMIC-FORCE MICROSCOPY STUDIES ON VARIOUS TYPES OF PHOTOLUMINESCENT POROUS SILICON

The structural characteristics of anodically-etched porous silicon (PS) layers emitting at different energy levels and with various luminescence fatigue strengths, recently classified into types A, B and C are compared using atomic force microscopy. Quantum-size micro-particles have been observed in type A PS within amorphouslike contrast, but only fairly rough amorphous grain-like structures have been observed in type B and C PS. Drastic quenching of photoluminescence in the PS layer after deposition of a capping layer of amorphous silicon is also reported.9430330

An interference method for the determination of thin film anisotropy

A new method of determination of thin film anisotropy from the angular dependence of the reflectance interference patterns for s- and p-polarized light is proposed and tested experimentally. The method is based on the different phase angle dependence of polarized light on the incident angle. As a result, the interference patterns of the reflected s- and p-polarized light beams exhibit a different number of oscillations in their angular dependence. The high sensitivity of the method is shown by its application to the interference patterns of a specially prepared multilayer structure with a calculated anisotropy.2794167111912