Improvement of the temporal and spatial contrast of high-brightness laser beams

Abstract

A novel method is suggested for temporal and spatial cleaning of high-brightness laser pulses, which seems more energy-scalable than that based on crossed polarizers and offers better contrast improvement compared to the plasma mirror technique. The suggested arrangement utilizes nonlinear modulation of the beam in the Fourier-plane leading both to directional and to temporal modulation. By the use of a ‘conjugate’ aperture arrangement before and after the nonlinear spatial selector, intensity dependent transmission is obtained; simultaneous temporal and spatial filtering can be realized both for amplitude and phase modulation. In the case of phase modulation introduced by plasma generation in noble gases the experimental observations are in good agreement with the theory; demonstrating >103 improvement in the temporal contrast, ~40% throughput, associated with effective spatial filtering. Due to the broad spectral and power durability of the optical arrangement used here, the method is widely applicable for energetic beams even of UV wavelengths, where most of the former techniques have limited throughput.

Petawatt and exawatt class lasers worldwide

“…Alternative schemes have been developed for short-pulse gas lasers, such as the nonlinear Fourier filter [309] . Here an annular beam is formed using an apodizing mask.…”

Large Spectral Shift of Reflected Radiation From Laser Plasmas Generated by High Contrast KrF Laser Pulses

“…The pulse is sent through a so-called pre-imaging system which after the first pass consists of a two lens telescope and a conventional spatial filter. After the second pass of the first amplifier, the beam is sent through the recently introduced non-linear Fourier-filter which provided-after focusing-our high temporal contrast (∼10 12 ) of the laser intensity [7,17]. Depending on the use of the Fourier-filter, the energy contrast ranged from 1:80 to 1:8 (when pulse cleaning was omitted).…”

“…For this reason we aimed to get more insight into KrF laser-plasma interactions under "clean" conditions where the temporal background before the main pulse does not modify the interactions. As an appropriate light source, the recently upgraded KrF laser system incorporating the newly installed Fourier-filtering technique [7] could be used, offering a short laser pulse with 10 12 temporal contrast.…”

“…However later it was shown [5] that a UV prepulse of low (i.e., ∼10 7 Wcm −2 ) intensity may result in photoablation and photoionization, thus preformed plasma in the interaction range. New developments of pulse cleaning based on the Fourier-filtering technique [7] and its integration into our laser system [15] allowed us to achieve 10 12 temporal contrast against the ASE prepulse of the KrF system. Detailed studies of the reflectivity and investigations of the spectral shape are then carried out on high-Z (Au) and low-Z (B) targets with the KrF laser system offering 700 fs ontarget pulse duration and 1.15 × 10 18 Wcm −2 intensity.…”

Intenzív ultraibolya lézerimpulzusok intenzitáskontraszt javítása

“…Ultrarövid, nagy energiájú impulzusok segítségével az optikai spektrum másik oldalán található THz frekvenciájú ultragyors elektromos terek keltésére és alkalmazására is lehetőség nyílik [28]. A rövid impulzusú KrF lézerrendszerek kontrasztjának javítására korábban sikerrel alkalmazták a plazma tükör technikát [36,37] valamint a nemlineáris Fourier-szűrést [38]. [30].…”