High intensity femtosecond laser are now routinely used to produce energetic particles and photons via interaction with solid targets. However, the relatively low conversion efficiency of such processes requires the use of high repetition rate laser to increase the average power of the laser-induced secondary source. Furthermore, for high intensity laser-matter interaction, a high temporal contrast is of primary importance as the presence of a ns ASE pedestal (Amplified Spontaneous Emission) and/or various prepulses may significantly affect the governing interaction processes by creating a pre-plasma on the target surface. We present the characterization of a laser chain based on Ti:Sa technology and CPA technique, which presents unique laser characteristics : a high repetition rate (100 Hz), a high peak power (>5 TW) and a high contrast ratio (ASE<10-10) obtained thanks to a specific design with 3 saturable absorbers inserted in the amplification chain. A deformable mirror placed before the focusing parabolic mirror should allow us to focus the beam almost at the limit of diffraction. In these conditions, peak intensity above 1019W.cm-2 on target could be achieved at 100 Hz, allowing the study of relativistic optics at a high repetition rate.
We report a novel experience gathered in the development of powerful optical sources of the vacuum
ultraviolet (VUV) radiation, which are based on high-current multichannel surface discharges of submicrosecond
duration. The peak intensity of the VUV radiation produced by the designed large-area (~0.1 m2) optical sources
reaches 130 kW/cm2, whereas the intrinsic efficiency of the discharge emission within the spectral range of 120-200 nm attains 3.2 %. Application of such sources to pump a gaseous active medium of the multipass XeF(C-A)
amplifier allows us obtaining the total gain factors exceeding 102 for the blue-green ultrashort optical pulses of
150 fs duration. The results presented in the report show a considerable potential of the developed laser
technology for the femtosecond pulse amplification up to petawatt peak powers.
Gain characteristics of a photolytically driven XeF(C-A) laser amplifier are studied experimentally in the unsaturated amplification regime. The gaseous active medium is optically pumped by the vacuum-ultraviolet (VUV) radiation from two large-area multichannel surface discharges initiated along opposite walls of the amplifier chamber. Total gain factor of 102 is obtained for the ultrashort optical pulses under multipass amplification in the active volume of 40×18×4 cm3 dimensions with a spatially homogeneous gain distribution. Spectral measurements reveal a good conservation of the seed pulse spectrum. Small-signal gain reaching 2×10-3 cm-1 is observed for the blue-green seed pulses of 150 fs duration, as well as for the continuous seed radiation at 488 nm. The obtained gain values, being compared with the gain calculated for the measured pumping radiation power, indicate that the quantum yield of the XeF(B) formation as a result of the XeF2 photodissociation is high and approaches unity within the spectral band of the XeF2 VUV photodissociation continuum.
Total gain exceeding 102 and a small-signal gain of 2x10-3 cm-1 are observed in a photolytically driven femtosecond XeF(C-A) amplifier in the regime of a homogeneous gain distribution over the active volume. These values, being
compared with the results of measurements of the pumping radiation power, show that the spectral quantum efficiency of
the XeF(B) formation as a result of the XeF2 photodissociation (related to an absorbed photon) approaches unity in the VUV spectral range.
We present the design of an OPCPA (Optical Parametric Chirped Pulse Amplification) pre-amplifier incorporated in a
visible (475 nm) high-contrast multiterawatt femtosecond laser chain based on hybrid (solid/gas) technology.
Amplification of blue-green (470-490 nm) femtosecond pulses in a gaseous active medium of a photolytically driven XeF(C-A) laser amplifier is studied experimentally. The active medium is optically pumped by the vacuum-ultraviolet radiation from two large-area multichannel surface discharges initiated along opposite planes of the amplifier cavity. The amplification factors exceeding 100 are obtained in a multipass optical scheme in the regime of homogeneous gain distribution over a beam cross-section of up to 3 cm in diameter. A small-signal gain of 0.002 cm-1 is observed at 488 nm for the continuous radiation of Ar-ion laser and for the 150 fs seed pulses as well. The registered spectra insure a good conservation of the temporal characteristics of amplified ultrashort pulses.
A new concept of the direct amplification of femtosecond optical pulses in photochemically driven active media, such as Xe2Cl, XeF(C–A) and Kr2F, is discussed with the main emphasis on the XeF(C–A) active medium as one of the most widely studied system. The main advantage of these systems is that they are characterized by a broad gain bandwidths (60–100 nm) which allow to support 10 fsec pulses and are centered in the blue-green region (490, 480 and 420 nm, respectively) spectrally matching to the second harmonic of a Ti:Sa laser. The last circumstance is important from the viewpoint of considerable increasing temporal contrast ratio of ultrahigh peak-power fsec systems.
A low density medium like a gas is attractive for laser amplification due to its high breakdown threshold and scalability to very large volumes. Moreover, the non-linear index of refraction of a gas is of three orders of magnitude lower than for a solid medium that is particularly suitable for direct amplification, without pulse stretching, of high-power ultrashort pulses. Among all gas laser media, application of the photolytical XeF(C-A) laser for high energy amplification is very attractive for the development of ultra-high power laser systems up to the petawatt power level due to the XeF(C-A) broad amplification bandwidth (80 nm FWHM centered near 475 nm) and a rather high saturation fluence (~0.05 J.cm-2), as well as a very low level of Amplified Spontaneous Emission. The paper presents the strategy of the LP3 laboratory to develop a high-contrast multiterawatt femtosecond laser chain based on a hybrid (solid/gas) technology, including a Ti:Sapphire oscillator generating 50 fs pulses at 950 nm, an Optical Parametric Chirped Pulse Amplification stage, a frequency converter, and a final high-energy amplification in the photolytical XeF(C-A) amplifier. Our approach is supported by first pilot experiments of femtosecond pulse amplification in a compact photolytical XeF(C-A) amplifier.
We introduce a numerical investigation of a HF photochemical laser pumped by planar multi-channel sliding discharge to study the possibility of advanced laser characteristic achievement using such pumping source. The model considers transport of VUV pump radiation through the nonlinear absorptive active medium containing NF3/H2/N2Ar gas mixture coupled with chemical and lasing kinetics describing the temporal and spatial evolution of particle species and intracavity lasing photons. The relative importance of various kinetic processes is evaluated and the 3.2 J/liter laser specific energy is calculated.
A numerical code has been developed to simulate the characteristics of HF chemical laser based on non-chain reaction pumped by a planar sliding discharge radiation. The model considers transport of VUV pump radiation through the nonlinear absorptive active medium containing NF3/H2/N2/Ar gas mixture coupled with chemical and lasing kinetics describing the temporal and spatial evolution of particle species concentration and intracavity lasing photons density. The relative importance of various kinetic processes is evaluated and a 3.2 J/l laser output specific energy is calculated along the laser axis.
Laser action in the optically pumped HF chemical laser using NF3 molecule as an F atom donor, as well as a bleaching wave regime of pumping HF chemical laser have been observed for the first time. The formation of a bleaching wave running away from the surface discharge, used as a pumping source, at the velocity of approximately 8 km/sec results in very fast (with supersonic velocity) replacement of an active medium in the zone of laser action and provides, thereby, as high as unity quantum efficiency of the laser action. Output energy of 0.4 J in a 3.2 microsecond pulse and specific energy of 3.5 J/l were observed. Also presented are the preliminary results of the first observation of the laser action in HF upon optical pumping of ClF5/H2 mixture by radiation from a surface discharge.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.