T. R. Nelson

Dynamics of optimized stable channel formation of intense laser pulses with the relativistic/charge-displacement mechanism

Studies of the dynamics of stable relativistic/ponderomotive channel formation demonstrate that the use of an appropriate longitudinal gradient in the electron density can significantly enhance the efficiency of the power compression. A unidirectional stable zone locking rule, which allows the operating point of the system to enter the region of stable channelled propagation, but blocks departures from it, is established. These characteristics are extremely favourable for kilovolt x-ray amplification, charged-particle acceleration and the initiation of nuclear reactions.

Thermal effects in laser pumped Kerr-lens modelocked Ti:sapphire lasers

Abstract Numerical beam propagation simulations are used to demonstrate that the distributed thermal lensing, produced by the absorption of the pump laser in the gain medium, profoundly affects the operation of hard-apertured, Kerr-lens modelocked Ti:sapphire lasers. The pump-induced thermal lensing is shown to shift and distort the resonator stability regions (even allowing the regions to overlap) and severely perturb the modelocking mechanism in one of the stability regions.

A multi-kilohertz electro-optic switch for ultrafast laser systems

Summary form only given.We report on the use of a multi-kilohertz intracavity electro-optic switch to both efficiently cavity-dump a femtosecond Ti:sapphire oscillator and perform the switching for a high-repetition-rate Ti:sapphire regenerative amplifier. The polarization switch consists of a transverse-field KD*P Pockels cell and a novel near-Brewster sapphire Rochon polarizer. In contrast to more conventional longitudinal Pockels cells with dielectric thin-film polarizers, this switch is capable of 50 kHz operation and near 100% switching efficiency due to the Rochon polarizers high extinction ratio (>10/sup 4/:1) and low insertion loss (nominally 100% transmission for the undeviated p-polarization and 100 nm about the central design wavelength), and high damage threshold (>10 GW/cm/sup 2/) are attractive properties for ultrafast laser systems, especially regenerative amplifiers.

High intensity ultraviolet laser and next generation sources

Performance of a Ti:Sapphire/KrF* laser system leading to the generation of what could prove to be the first multi-terawatt pulses reported in this spectral region will be presented. An attractive alternative to hybrid excimer lasers is offered by direct UV generation from laser crystals that can support generation and amplification of ultrashort pulses. The design of a high-intensity ultraviolet laser system based on Cerium-doped colquiirites is examined.

Design and Analysis of a Deep UV Laser based on Ce3+: LiSrAIF6

Ce3+:LiSrAlF6 (Ce:LiSAF) has been demonstrated to amplify light between the wavelengths of 285 and 297 mn by several groups. A source in this region of the ultraviolet is attractive for biophysics, physical chemistry, and ultra-strong-field physics, particularly if femtosecond operation can be achieved. Motivated by the successful operation of Kerr-Lens mode-locked (KLM) Cr3+:LiSAF oscillators in the red and near infrared, we have undertaken the analysis and design of a KLM oscillator and amplifier system based on Ce:LiSAF. Since Ce:LiSAF has an absorption band centered near 260 nm, a limited selection of pump sources is available. A comparison of those sources is presented. The two-photon absorption band edge of the colquiriite host can be estimated to be in the region of 105 – 130 nm, a range based on the absorption properties of its constituents. This suggests minimal two-photon absorption of the UV radiation by the host. As a result, the second order index of refraction (n2) should be positive so that conventional KLM operation of a laser cavity will be possible. In addition, since the bandwidth is capable of supporting sub-100 femtosecond pulses, the material is a promising gain medium for amplification to high peak powers. Accordingly, an outline of the development of a terawatt class 290 nm, sub 100 fs laser system is given.

Theoretical/experimental studies of ultraviolet high-power-density self-trapped channels

Experimental evidence indicates that the dynamics of channeled propagation arising from a relativistic/charge-displacement mechanism can produce exceptionally high intensities (>10{sup 20} W/cm{sup 2}) and power densities (>10{sup 19} W/cm{sup 3}) under spatially well-controlled conditions in the interior of the channel. This process opens up a new domain of high intensity interactions in which controllable field strengths in the 10-50(e/a{sub 0}{sup 2}) range can be applied to materials. Furthermore, these field strengths can be developed on very fast rise times ({approx}1-3 fs), since the dynamical response of the channel formation can be on the order of the plasma time {approx}2{pi}/{omega}{sub p}. Under these conditions, matter is expected to respond in a highly complex and nonlinear way. Of particular significance are (1) the detailed dynamics of the channeling mechanism, including the wavelength scaling, and (2) the development of advanced analytical tools to represent the interactions theoretically.

Multiterawatt Ultraviolet Lasers

The advances in ultrashort pulse generation and chirped pulse amplification (CPA) techniques have been the driving force in the development of laser systems with peak powers at and beyond the Terawatt (1012 W) level1–7. Most high power systems developed to date, work in the infrafed, and Terawatt and Petawatt (1015 W) class lasers have been demonstrated in Ti:Sapphire, Nd:glass and Cr:LISAF based systems. These systems are moving towards shorter pulse durations, now commonly of the order of tens of femtoseconds, and design goals are heading towards high repetition rate (kHz)8 multiterawatt systems. The progress in this field has certainly been inspired by the improvements in solid-state laser materials for ultrashort pulse generation. An analogous statement does not generally hold, however, for the ultraviolet wavelengths.