5/27/2023 0 Comments Fifth element multipass![]() ![]() More detailed description of the principle of pulse stretching and compression by a volume diffractive grating with variable period is given in the '185 patent. A stretched pulse being launched to the same or similar grating in opposite direction will be recompressed to its original duration. This wavelength-dependent delay forms a temporally and spatially stretched pulse with instant power that is decreased proportionally to a stretching ratio in comparison with that in the original pulse. The optical path length differences between the different spectral components leads to a wavelength-dependent group delay. Due to this period variation in the direction of laser beam propagation, different spectral components of a pulse incident on the grating are reflected by different parts of the grating along this direction. The high-efficiency PTR-glass reflecting volume Bragg gratings with spatially variable periods described in the '185 patent have been used to demonstrate stretching of ultrashort pulses of 100 and more femtoseconds in duration to 100s of picoseconds and high-efficiency re-compression to near-transform-limited pulse duration. Smirnov and titled “Spectral and angular filters based on high efficiency diffractive elements with variable period in photo-thermo-refractive glass”. Smirnov, Almantas Galvanauskas, Kai-Hsiu Liao, titled “Stretching and compression of laser pulses by means of high efficiency volume diffractive gratings with variable periods in photo-thermo-refractive glass” and co-pending U.S. The principle of pulse stretching and compression by high-efficiency PTR-glass volume diffractive gratings with variable periods as described in U.S. Smirnov, titled “High efficiency volume diffractive elements in photo-thermo-refractive glass” both having at least one common inventor as the present invention and assigned to the same assignee and which are incorporated herein by reference. Smirnov and titled “Process for production of high efficiency volume diffractive elements in photo-thermo-refractive glass” which describes a method of fabrication of high efficiency volume diffractive gratings in PTR glass and U.S. The present invention is related to U.S. However, a problem with the prior art is that sizes of such stretchers and compressors are large than sizes of amplifiers and the average power of such laser systems is limited by the relatively low damage threshold of the metal-coated gratings. ![]() Conventional technology uses metal-coated gratings. Traditionally, pulse stretching and compression in chirped pulse amplification systems is performed with a pair of surface diffraction gratings. Pulse compression is performed with dispersive optical elements that are required to have a high laser-induced damage threshold. After amplification the pulses are compressed, resulting in high peak power. ![]() Using this technique, ultrashort pulses are stretched by dispersive optical elements before amplification so that the peak power of the pulses in the amplifier is moderate and does not lead to damage. In order to mitigate these effects, a technique of chirped pulse amplification (CPA) was developed. Direct optical amplification of high-power ultrashort pulses results in detrimental nonlinear effects and laser-induced damage of amplifying medium due to extremely high peak power of amplified pulses. High-power ultrashort laser pulses have found applications in many fields of modern science.
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