J.M.D. Lister

A high performance excimer pumped Raman laser

An electron beam pumped large aperture KrF laser operating in a short pulse multiplexed mode has been used to pump a methane Raman laser to produce a single high intensity pulse at 268 nm. With an output beam divergence of 20 μrad and final amplifier conversion efficiency of greater than 50%, intensity at the focus of an F/3 lens was greater than 1017 W/cm2. Prepulse intensity was less than 10−10 of peak intensity.

A 1 TW KrF laser using chirped pulse amplification

Abstract Chirped pulse amplification (CPA) and recompression have been used in a large aperture KrF laser system. The power focused onto target in a 300 fs pulse reached 1 TW with an irradiance of ≈ 10 19 W/cm 2 .

Variable length transform-limited pulses from a stabilized synchronously-pumped mode-locked laser

Abstract We have investigated the stabilization of a synchronously-pumped mode-locked dye laser by self feedback. The output consists of transform-limited pulses whose shape and duration depend on the tuning of the main laser cavity. Measurements of the limiting of the feedback with respect to the main cavity indicate that the optimum timing depends on the length of the pumping pulses rather than that of the output pulses.

Picosecond gain and saturation measurements in a KrF laser amplifier depumped by amplified spontaneous emission

The input/output characteristic of a large aperture (270‐mm diam) electron‐beam‐pumped KrF laser amplifier is obtained for pulses of 6‐ and 40‐ps duration. The off‐resonance absorption coefficient is estimated by measurement of loss at 268 nm. The gain‐to‐loss ratio is found to decrease from 8 to 6 as the specific pump rate is increased from 0.3 to 0.65 MW cm−3. Gain depumping due to amplified spontaneous emission (ASE) is treated by a simple 1D code and found to give good agreement with experiment. A 3D code incorporating wall reflections gives even better agreement. The spatial distribution of gain and ASE is recorded using visible and ultraviolet imaging.

Ultrahigh-brightness laser beams with low prepulse obtained by stimulated Raman scattering.

A unique high-power laser system is described that is based on stimulated Raman scattering in methane. KrF-laser pump beams of 10-ps duration are confined in a square-section light guide and amplify a 268-nm Stokes-shifted beam to 0.5 TW with extremely low prepulse. The near-diffraction-limited beam quality gives a peak brightness of >1020 W cm−2 sr−1.

Short pulse amplification in the ultraviolet using stimulated Raman scattering

Abstract Experimental results are presented for high gain high conversion amplification of short ultraviolet laser pulses in a methane filled Raman amplifier. The results are found to be in good agreement with a numerical solution of the equations for transient plane wave stimulated Raman scattering, using an experimental estimate of the Raman gain coefficient, for a range of input intensities and three pulse lengths.

Uniform target illumination by induced spatial incoherence in a multiplexed KrF laser system

Abstract A technique for producing uniform target irradiation by applying induced spatial incoherence to a high power multiplexed KrF laser system has been demonstrated. The image of a smooth spatial profile is relayed on four beams through a large aperture, electron beam pumped KrF laser and to the focal plane of a concave mirror. Single pulses of 20 ns duration have been amplified to energies of 30 J while observing the effect of amplification on the output profile uniformity.

On the origin of the dip in the KrF laser gain spectrum. II. The short-pulse gain saturation experiment

The wavelength resolved spectra recorded during subnanosecond depletion of the gain in a KrF laser amplifier have been used to specify the state responsible for the dip in the KrF(B→X) emission spectra. Self-absorption of the KrF laser emission at 248.9 nm has been found to be due to the phototransition from the KrF(C) state to a 2Π Rydberg state.

ON THE ORIGIN OF THE DIP IN THE KRF LASER GAIN SPECTRUM

High‐resolution spectra of KrF (B–X) amplified spontaneous emission from various discharge‐pumped and electron‐beam‐pumped KrF lasers have been analyzed. An underlying structured absorption spectrum has been discovered with a well‐resolved peak at 248.91 nm. The absorption coefficient of this peak was found to vary in exact proportion to the peak laser gain coefficient but was independent of laser gas purity. We suggest that the absorption arises internally within the KrF molecule and is due to transitions from the B state to a higher‐lying Rydberg state. This hypothesis was tested by simulating the absorption spectrum from KrF*(B) to a weakly repulsive state dissociating to Kr*(3P1)+F(2P3/2). A good agreement was obtained between simulated and experimental absorption spectra.

Sprite: A Very High Brightness, Ultraviolet Laser System

The Sprite KrF/Raman laser system has been developed, over the last 12 years, into one of the worlds brightest laser sources. It is now a fully scheduled user facility delivering more than 1900 shots per year to a dedicated target chamber. A laser development programme is also supported, addressing the future requirements of the high-power laser community. Sprite has traditionally been operated as a KrF-pumped Raman laser, delivering 10 ps pulses of very high brightness (∼ 1020W cm−2 sterad−1) and exceptional prepulse contrast ratio (< 1010). Direct amplification of pulses as short as 3 ps is practical in the Sprite KrF chain, and a chirped pulse amplification scheme has now been implemented delivering 300 fs pulses to target with a power of 1 TW. The next major upgrade to the system will be the installation of a new 40 cm aperture amplifier, Titania, designed to deliver up to 400 J in four Raman pulses.