Mikhail Kalashnikov

Double chirped-pulse-amplification laser: a way to clean pulses temporally

We demonstrate a double chirped-pulse-amplification (CPA) Ti: sapphire laser system that includes two CPA stages with intermediate nonlinear temporal pulse filtering. The method makes it possible to reduce substantially the background of amplified spontaneous emission (ASE), including prepulses and postpulses. An ASE temporal contrast of 10(10) was demonstrated at 20 mJ of output energy and 50-fs pulse duration. The demonstrated scheme is applicable to petawatt power-level laser systems.

Dispersion measurement of inert gases and gas mixtures at 800 nm

Dispersion of femtosecond laser pulses propagating in Ar, He, Kr, N(2), Ne, Xe, and their mixtures is measured by spectrally and spatially resolved interferometry. By varying the gas pressure in a 4.5 m long tube between 0.05 mbar and ambient pressure, the first, second, and third order phase derivatives of broadband laser pulses are determined at 800 nm under standard conditions. The dispersion of gases and gas mixtures obeys the Lorentz-Lorenz formula with an accuracy of 0.7%. Based on the measured pressure dependent dispersion values in the near infrared and the refractive indices available from the literature for the ultraviolet and visible, a pressure dependent Sellmeier-type formula is fitted for each gas. These common form, two-term dispersion equations provide an accuracy between 4.1x10(-9) (Ne) and 4.3x10(-7) (Xe) for the refractive indices, from UV to near IR.

Characterization of a nonlinear filter for the front-end of a high contrast double-CPA Ti:sapphire laser.

A nonlinear filter using rotation of the polarization ellipse in air is investigated. Scheme to enhance the temporal contrast is developed for a double-CPA multi-terawatt Ti:sapphire laser. It supports an energy level of millijoule and has a high efficiency. The method allows suppression of the ASE pedestal, pre- and post-pulses by 3 orders of magnitude and also steepens the pulse front. For the physical interpretation of the results, numerical simulation of the filtering is performed.

High peak and average power Ti: sapphire thin disk amplifier with extraction during pumping

The combination of the extraction during pumping (EDP) amplification scheme and the thin disk (TD) technology has been successfully applied to the Ti:sapphire (Ti:sa) laser medium for the first time, to the best of our knowledge. In a proof-of-principle experiment, we demonstrate high energy broadband amplification in a room temperature water cooled EDP-TD head of stretched femtosecond pulses at a 10 Hz repetition rate, instead of performing a cryogenically cooled traditional multi-pass scheme. Hence, the EDP-TD combination can overcome the limits associated with thermal effects and transverse amplified spontaneous emission, enabling Ti:sa laser systems to have a petawatt peak and hundreds of watts of average power.

Design of a thin disk amplifier with extraction during pumping for high peak and average power Ti:Sa systems (EDP-TD)

Combination of the scheme of extraction during pumping (EDP) and the Thin Disk (TD) technology is presented to overcome the limitations associated with thermal cooling of crystal and transverse amplified spontaneous emission in high average power laser systems based on Ti:Sa amplifiers. The optimized design of high repetition rate 1-10 PW Ti:Sapphire EDP-TD power amplifiers are discussed, including their thermal dynamic behavior.

High peak power Ti:sapphire lasers : temporal contrast and spectral narrowing issues

Two new schemes of chirped pulse amplification (CPA) lasers are demonstrated, which are specially designed to overcome some of the bottlenecks of the current Ti:sapphire lasers. In particular, the issues of temporal contrast and spectral narrowing of the pulse during amplification are considered. The proposed schemes are double CPA (DCPA) and the negatively- and positively-chirped pulse amplification (NPCPA). Both of them are an extension of the conventional CPA scheme to Ti:sapphire lasers of petawatt and higher power levels. The double DCPA laser includes two CPA stages with intermediate non-linear temporal pulse filtering. The method reduces substantially the background, including amplified spontaneous emission as well as pre- and post-pulses. The former is demonstrated by achieving a temporal contrast of at least 1010 with pulses of 2O mJ output energy and 50fs pulse duration. The NPCPA laser scheme implements a combination of negatively- and positively-chirped pulse amplification. This method of amplification suppresses gain related spectral narrowing, typical to CPA lasers, thus supporting pulse spectrum much broader than a conventional CPA. With a NPCPA Ti:sapphire laser we have achieved laser pulses of 50 nm spectral width and 150 mJ energy without any additional spectral correction. The scheme appears as an easy and reliable solution to preserve spectral bandwidth in Ti:Sapphire lasers, especially at high power levels up to the Petawatt regime.

Temporal contrast of high intensity laser systems above 1011 with double CPA technique

Using a combination of the Negative-Positive, the Double Chirped Pulse Amplification techniques with nonlinear XPW temporal filtering in the laser front end allows substantial suppression the ASE level pushing the temporal contrast of amplified 100 TW pulses at 10 Hz operation above 1011.

Liquid-cooled Ti:Sapphire thin disk amplifiers for high average power 100-TW systems

In this work, numerical heat transfer simulations of direct water-cooled gain modules for thin disk (TD) Ti:Sapphire (Ti:Sa) power amplifiers are presented. By using the TD technique in combination with the extraction during pumping (EDP) method 100-TW class amplifiers operating around 300 W average power could be reached in the future. Single and double-sided cooling arrangements were investigated for several coolant flow velocities. Simulations which upscale the gain module for multiple kilowatts of average power were also performed for large aperture Ti:Sa disks and for multiple disks with several coolant channels.

Measurement Of The Spectral Phase Shift And The Residual Angular Dispersion Of An AOPDF

The spectral phase shift and both types of angular dispersion introduced by an acousto‐optic programmable dispersive filter (AOPDF) into a femtosecond laser beam at 800 nm have been measured with high precision. With the use of spectrally and spatially resolved interferometry we experimentally proved that the AOPDF controls the group delay dispersion (GDD) and third‐order dispersion with an accuracy of better than 1% and 3% of the preset values within the range of 2 fs2–1000 fs2 and 1000 fs3–40000 fs3, respectively. Both the angular deviation as well as the angular dispersion values are primarily dependent on the set absolute value of GDD of the continuously operating AOPDF. Besides of a small offset value, there is no added angular dispersion at 0 fs2, while this can be as large as 0.2 μrad/nm at 10000 fs2.

Broadband amplification of 800-nm pulses with a combination of negatively and positively chirped pulse amplification

It is experimentally proved that successive amplification of negatively and positively chirped laser pulses (NPCPA) counteracts the gain narrowing effect typical in chirped pulse amplification (CPA) lasers. The scheme is robust and easy to adopt to even petawatt (PW) level high power laser systems. As a demonstration, a multi-terawatt (TW) Ti:sapphire laser system was modified to the NPCPA. The bandwidth of the 150 mJ output pulses exceeds 50 nm without any additional spectral correction, which is 30% broader than those currently available from conventional CPA lasers. Moreover, the NPCPA scheme gives an opportunity to increase an intensity temporal contrast without any compromise in pulse energy.