High-power Ultrashort Laser Pulses Research Articles

Modeling cluster jets as targets for high-power ultrashort laser pulses

A hydrodynamic model is formulated that describes the formation of clusters in atomic gas jets expanding into vacuum, which are used as laser plasma targets. Detailed model calculations performed for an argon gas jet describe spatial distributions of the density of gas and cluster phases formed in the Laval nozzle at room temperature in a broad range of entrance gas pressures. The cluster density distribution is significantly inhomogeneous. The cluster distribution features revealed by the model calculations were qualitatively confirmed by the X-ray spectroscopic measurements of the spatial distribution of emission from the plasma created in the jet tar-gets by high-power ultrashort laser pulses.

Skin effect, ion-acoustic turbulence, and anomalous transport in a nonisothermal solid-state plasma generated by a high-power femtosecond laser

We propose an interpretation of the experimental data reported by Milchberg, Freeman et al. [1] on the absorption of intense 400-fs laser radiation pulses in an aluminum target. It is shown that the electric conductivity of a nonisothermal aluminum plasma possessing a solid-state density in these experiments was determined by the ion-acoustic oscillations (ion-acoustic turbulence). It is therefore necessary to study theoretically the ion-acoustic turbulence effect in a nonisothermal plasma possessing solid-state density. Possible approaches to a theoretical description of this effect and the interactions of a such a plasma with high-power ultrashort laser pulses are discussed.

Imaging a tunneling ionization front by using a schlieren method

A schlieren method was used to generate time-resolved images of the tunneling ionization front produced when an ultrashort high-power laser pulse irradiates He gas. By superimposing sequential schlieren images, we obtained information about the laser propagation and found that the ionization front propagated farther with decreasing density of the target gas. Ray-tracing suggested that this density dependence is a result of the spatial distribution of the laser intensity.

Hard X-ray generation and particle production via the relativistic-intensity laser pulse interaction with a solid target

This paper considers various channels of electron–positron pair, neutron, and γ-quantum generation via the ultrashort high-power laser pulse interaction with targets made from different materials. The positron yields in materials with different Z are estimated for the positron production by high-speed electrons and γ-photons. It is shown that a picosecond 100-TW laser pulse gives rise to formation of about 1010 positrons, possible channels of the neutron production in light- and heavy-atom materials being studied as well. It is ascertained that the formation of up to 107 laser neutrons per shot is possible when the laser intensity is ∼1021 W/cm2 on a heavy-atom target.

Laser acceleration of electrons in a thin metal film

A mechanism acceleration of electrons to relativistic velocities in a thin metal film irradiated with ultrashort (τ L ≤1 ps) high-power (I>16 W/cm2) laser pulses is proposed. The acceleration is due to a resonance action of the nonuniform field on a portion of the electrons, viz., those which oscillate in the direction transverse to the film with a frequency close to the frequency of the field.

Dynamics of high-power ultrashort laser pulses in resonant media

Dynamics of high-power ultrashort laser pulses in resonant media

Matter in ultrastrong laser fields

An analysis is made of the physical principles of stimulated emission of laser pulses with extremely high power (up to 1015 W) and of very short duration (less than 1 ps). Relationships governing the interaction of such pulses with matter are discussed. It is shown that the phenomena that occur on exposure of transparent media and condensed targets to high-power ultrashort laser pulses are different in kind. Qualitatively new physical effects, whose appearance is related to nonlinear (including relativistic) effects in the laser-beam electric field are given special attention. The results of recent experiments and studies planned for the future are considered in conjunction with a theoretical analysis.

Self-induced mismatching effects in harmonic generation with ultra-short laser pulses

Relying on exact numerical calculations, we report some simple formulae by which it is possible to take into account any self-induced mismatch effect in second harmonic generation with high power ultra-short laser pulses. In particular, we have considered the following effects: bandwidth effect, thermal effect, frequency chirping, angular tilting, pulse lengthening.

Elimination of laser prepulse by relativistic guiding in a plasma

A method is proposed for eliminating prepulses associated with high-power ultrashort laser pulses. In this method the high-power portion of the pulse is refractively guided due to relativistic effects associated with the plasma electrons. The low-power prepulse, however, is unaffected and diffracts away. Optical guiding is achieved by appropriately choosing the plasma density, laser power, and wavelength. In addition, a wavebreaking stabilization mechanism for the Raman backscattering instability for intense laser pulses is proposed, which indicates that the pulse should not be significantly backscattered by the plasma.

Parametric amplification of ultrashort 10-μm pulses by two-photon absorption of pump radiation

A numerical investigation was made of the generation of picosecond radiation pulses in the 10-μm wavelength range by parametric amplification of injected 10-μm radiation in the field of high-power ultrashort neodymium laser pulses in a nonlinear proustite (Ag3AsS3) crystal. Calculations were carried out in the approximation of plane interacting waves and they allowed for two-photon absorption of the pump pulses and phase modulation of the interacting pulses by an electron density wave. These effects lower the efficiency of parametric amplification by two orders of magnitude (when the pump pulse intensity is 1.2 GW/cm2) and they also result in pushing of the signal pulse to the front of the pump pulse and cause its shortening without a significant widening of the spectrum.

Selective interaction of ultrashort ultraviolet laser pulses with components of macromolecules

The first successful experiments on selective interaction with a specific type of base in DNA and RNA are reported. It is shown that when dilute aqueous solutions of bases are irradiated by high-power ultrashort ultraviolet laser pulses, two-stage excitation of high electronic levels takes place, resulting in the formation of irreversible photoproducts. The quantum yield of photoproducts depends on many parameters and may be made essentially different for bases of different types. By varying the experimental conditions, selective interaction with a specific type of base was achieved both by irradiating mixtures of bases and by irradiating more complex components of nucleic acids.

High-speed scans of the luminescence spectra of rhodamine 6GandBsolutions excited by ultrashort light pulses

The results are given of an investigation of the kinetics of the luminescence spectra of rhodamine dyes carried out using a fast shutter based on the optical Kerr effect. The measurements were carried out during a period of 2–100 psec from the beginning of an exciting pulse and they demonstrated that during this period the luminescence spectra did not change but were identical with the time-integrated spectra determined under the same excitation conditions. However, the shape and position of the spectra changed considerably when excitation with continuous low-power radiation was replaced with high-power ultrashort laser pulses. This was due to the possibility of formation of excited stereoisomers of the dyes.