Post-compression of powerful femtosecond pulses after second harmonic generation.

A proof-of-principle experiment of highly efficient (38%) second harmonic generation was implemented at a ∼1T W/c m 2 intensity of a 45 fs pulse in a composite nonlinear sample-a 1 mm KDP crystal glued onto a 1 mm fused silica substrate. The attenuated replica of the second harmonic pulse (455 nm) was compressed down to 28.6 fs by means of dispersive mirrors, with a significant reduction in both the wings and the far temporal contrast. The peak power of the second harmonic was ∼74% of the power of the fundamental harmonic, which ensured a three-fold increase in the focal intensity.

Upgrading the front end of the petawatt-class PEARL laser facility.

A new front-end laser system with optical synchronization of chirped femtosecond and pump pulses for the petawatt laser complex PEtawatt pARametric Laser (PEARL) has been developed. The new front-end system provides a broader femtosecond pulse spectrum, temporal shaping of the pump pulse, and a significant increase in the stability of the parametric amplification stages of the PEARL.

Laser wakefield acceleration based x ray source using 225-TW and 13-fs laser pulses produced by thin film compression.

We show that 13-fs laser pulses associated with 225 TW of peak power can be used to produce laser wakefield acceleration (LWFA) and generate synchrotron radiation. To achieve this, 130-TW high-power laser pulses (3.2 J, 24 fs) are efficiently compressed down to 13 fs with the thin film compression (TFC) technique using large chirped mirrors after propagation and spectral broadening through a 1-mm-thick fused silica plate. We show that the compressed 13-fs laser pulse can be properly focused even if it induces a 10% degradation of the Strehl ratio. We demonstrate the usability of such a laser beam. We observe both an increase of the electron energy and of the betatron radiation critical energy when the pulse duration is reduced to 13 fs compared with the 24-fs case.

Temporal compression of high-power IR laser pulses in a KDP crystal.

It is shown that a KDP crystal can be used for temporal compression of powerful pulses of the near-IR range. A method of searching for laser beam and crystal parameters suitable for compression is proposed. Temporal compression of laser pulses at a central wavelength of 1034 nm from 266 fs to 94 fs during propagation along the optical axis in a 21 cm thick KDP crystal is demonstrated experimentally.

Temporal contrast enhancement and compression of output pulses of ultra-high power lasers.

The peak power and temporal intensity contrast of powerful femtosecond laser pulses were enhanced simultaneously by broadening the pulse spectrum in transparent dielectrics due to self-phase modulation and subsequent reflection from chirping mirrors with a symmetrical dip in the reflection coefficient in the center of the broadened spectrum. This dip provides almost zero reflection of the pulse pedestal, only slightly distorting the pulse itself.

Compression of high-power laser pulses using only multiple ultrathin plane plates.

A proposal for additional temporal compression and peak power enhancement of intense (>TW/cm2) femtosecond laser pulses using two thin plane-parallel plates is presented. The first ultrathin plate (order of mm) induces spectral broadening due to self-phase modulation, and the second ultrathin plate (order of micron) corrects the spectral phase. The elimination of the negative dispersive multilayer coating from the scheme offers an improved laser-induced damage threshold for the post-compression process.

Shaping of picosecond laser pulses with THz intensity modulation in the infrared, visible, and ultraviolet ranges.

The methods of shaping picosecond laser pulses with periodic intensity modulation tunable in frequency and depth are considered. Schemes for shaping modulated pulses "in-line" and with one output port are proposed. A picosecond modulation of the time envelope for IR laser pulses using a polarization interferometer is demonstrated experimentally. Shaping of modulated laser pulses of the UV range is shown by numerical modeling. The possibility to control the modulation depth of the fourth harmonic under the combined impact of material dispersion and nonlinear conversion in a classical collinear scheme of the fourth harmonic generation without distortion of the 3D pulse shape is demonstrated.

Highly efficient fourth harmonic generation of broadband laser pulses retaining 3D pulse shape.

A method for highly efficient fourth harmonic generation (FHG) retaining spatiotemporal intensity distribution of broadband chirped laser pulses is proposed. It is based on the use of pulses with linear frequency chirps of equal absolute magnitudes and opposite signs at the oo-e type noncollinear second harmonic generation. Fourth harmonic generation can by obtained by the classical method, since the second harmonic pulse is narrowband and spectrally limited. A possibility to retain the three-dimensional (3D) structure of the field at FHG with a conversion efficiency ∼60% is demonstrated by the numerical simulation of 3D pulses with a quasi-ellipsoidal intensity distribution.

Shaping picosecond ellipsoidal laser pulses with periodic intensity modulation for electron photoinjectors.

A method for shaping periodic intensity distributions of strongly chirped picosecond laser pulses in the infrared range by periodic phase modulation of the spectrum is proposed. The dependence of the time modulation period and depth on the parameters of periodic phase modulation of the spectrum is analyzed by analytical and numerical methods. It is demonstrated that the intensity distribution structure obtained at second- and fourth-harmonic generation can be retained by introducing an angular chirp. The electron bunch dynamics at the photoinjector test facility at DESY in Zeuthen (PITZ) was modeled numerically using ellipsoidal laser pulses with intensity modulation.

Retaining 3D shape of picosecond laser pulses during optical harmonics generation.

Collinear and noncollinear sum-frequency generation of broadband laser pulses with angular and frequency chirp is considered. The conditions of minimal distortions of 3D ellipsoidal intensity distribution of triangular chirped femtosecond pulses during generation of the second, third, and fourth harmonics of a Ti-Sa laser in LBO, BBO, and KBBF crystals are found using numerical methods. The efficiency of conversion from the fundamental to the fourth harmonic (45%) is higher than to the third harmonic (20%), and the distortions of intensity distribution are less.

Shaping of cylindrical and 3D ellipsoidal beams for electron photoinjector laser drivers.

With the use of spatial light modulators it became possible to implement in experiments the method of controlling the space-time intensity distribution of femtosecond laser pulses stretched to picosecond duration. Cylindrical and quasi-ellipsoidal intensity distributions were obtained and characterized by means of a 2D spectrograph and a cross-correlator.

Disk Yb:KGW amplifier of profiled pulses of laser driver for electron photoinjector.

We investigated a diode-pumped multipass disk Yb:KGW amplifier intended for amplifying a train of 3D ellipsoidal pulses of a laser driver for a photocathode of a linear electron accelerator. The multipass amplification geometry permitted increasing the energy of broadband (about 10 nm) pulses with a repetition rate of 1 MHz from 0.12 µJ to 39 µJ, despite large losses (two orders of magnitude) introduced by a beam shaper of 3D ellipsoidal beam. The distortions of the pulse train envelope were minimal due to optimal delay between the moment of pump switching on and arrival of the first pulse of the train.