Optimization of a chirped-pulse amplification Nd:glass laser

To allow us to achieve the highest focused intensity from a chirped-pulse amplification Nd:glass laser, a number of features of the system have been considered and optimized. These include the compressor geometry, the system aberrations, and the use of mixed glasses in the amplifier chain. Calculations for the laser with a single- or double-pass pulse compressor with 450-mm gratings are presented. These indicate that, for single pass, a reduction in pulse duration from 380 to 237 fs is possible when a phosphate is changed to a mixed phosphate-silicate glass system, and there is a corresponding increase of 44% in peak intensity at beam focus.     

Design and testing of a large-aperture, high-gain, Brewster 's angle zigzag Nd:glass slab amplifier

At the University of Rochester we have constructed and tested a large-aperture, (1.0 x 6.5 cm), high-gain (8) Brewster 's angle zigzag Nd:glass amplifier with a repetition rate of 2 Hz. This amplifier has a gain uniformity of +/-3 % and a maximum stress-induced depolarization <2.5 %.     

Finite size compression gratings in a large aperture chirped pulse amplification laser system

A simple model is presented to calculate the effects of the finite size of the diffraction gratings in the compressor of a chirped pulse amplification laser system. A wavelength-dependent clipping at the second grating alters the spectral distribution of the compressed pulses, affecting their time domain as well as their spatial distribution in the focal plane. Laser parameters of paramount importance to laser/plasma interaction experiments such as peak intensity, pulse duration, and prepulse levels are affected by the compressor design. Calculations of the effect of spectral clipping on these parameters for Gaussian, sech(2), and top-hat input spectra are discussed, and the benefit of double-pass compared with single-pass compression is also investigated. As an example, with 300-mm gratings and single-pass compression, for a sech(2) spectrum the pulse length of a 400-fs pulse increases to 459 fs, the peak intensity decreases by 25%, and the focal spot size increases by 8% because of the finite size of the gratings.     

Development of a pumping laser system for x-ray laser research

A two-beam chirped-pulse-amplification Nd:glass laser system dedicated to x-ray laser research is described. Each beam provides an output energy of 20 J with a typical pulse duration of 1.3 ps. A prepulse of variable duration is generated by use of a novel, to our knowledge, optical system. A reflection optical system, comprised of an off-axis parabolic mirror and a spherical mirror, produces a line focus with 6-mm length and 165-microm width without chromatic aberration. By use of this pumping laser system, the nickel-like silver x-ray laser at a wavelength of 13.9 nm has been demonstrated.     

Response of a fiber ring cavity to chirped Gaussian pulse laser injection

In this paper, the response of a fiber ring cavity to chirped Gaussian pulsed laser injection is investigated theoretically, and the expression of the field intensity out of the ring cavity is derived in the time domain. Numerical results demonstrate that different microwave and millimeter signals can be achieved, such as in the case of chirp parameter C?=?5 and input pulse width of 80?ps, the frequencies of generated microwave and millimeter-wave signals are ～16.1?GHz, ～26.3?GHz, ～33.3?GHz, and ～50?GHz. The results have potential application in tunable microwave/millimeter-wave generation.     

Design of PETAL multipetawatt high-energy laser front end based on optical parametric chirped pulse amplification

We report on a single shot optical parametric chirped pulse amplifier designed to seed the Petawatt Aquitaine Laser on the Laser Integration Line facility multipetawatt high-energy laser. The scheme is based on a stretched signal pulse at 1053 nm amplified with 20% conversion efficiency by a monomode pump pulse at 527 nm. The homemade pump laser is able to deliver a single shot beam with a square flat top spatial profile and programmable temporal shape. A high-stability 150 mJ, 8 nm, and 4.5 ns stretched pulse is then obtained with an excellent quality spatially shaped beam.     

Quasi-flat-top frequency-doubled Nd:glass laser for pumping of high-power Ti:sapphire amplifiers at a 0.1 Hz repetition rate

A Nd:glass laser based on a novel design delivers up to 120 J energy pulses with a quasi-flat-top spatial profile at a 0.1 Hz repetition rate. The laser output is frequency-doubled with 50% efficiency and used to pump Ti:sapphire amplifiers. The developed design is perspective for use in the currently contemplated next step in ultra-high-intensity laser development.     

Development and applications of a compact hybrid tabletop terawatt chirped-pulse amplification Ti:sapphire-Nd:glass laser for x-ray lasing and harmonic generation

A hybrid tabletop (2 m x 3 m) terawatt chirped-pulse amplification Ti:sapphire-Nd:glass laser (1054 nm, 475 fs, 500 mJ, 9 x 10(17) W cm(-2)) has been developed for laser-matter experiments. An overall gain factor of 10(10) was achieved for the laser. The results of laser applications in the studies of soft-x-ray Ni-like Mo 18.9-nm lasing and of harmonic generation from solid surfaces are presented.     

Efficiency optimization for a diode-pumped Nd:YAG ceramic slab laser

With the help of photometric calculations based on ray-tracing algorithms, we have optimized the efficiency of the optical pumping of a Nd:YAG ceramic slab laser. The slab pumping is performed by means of two horizontal diode laser array stacks. The use of two small reflecting walls allows the sort of duct coupling that is capable of significantly improving the performance of the system. Our first experiments with a simple direct coupling provided a maximum extraction of slightly more than 160 W at a 20% slope efficiency level. The use of the optimized short duct coupling leads us to the extraction of 350 W with a slope efficiency of 51%, making use of the same diode arrays. The laser design is suitable for the construction of cw sources with a power output above 1 kW.     

Spectroscopic analysis of a novel Nd3+-activated barium borate glass for broadband laser amplification

Spectroscopic parameters of a novel Nd³⁺-activated barium borate (BBONd) glass have been analyzed for broadband laser amplification. The Judd–Ofelt (JO) intensity parameters were determined through a systematic analysis of the absorption spectrum of Nd³⁺ ions in the BBONd glass. High values of the JO intensity parameters reveal a great centro-symmetrical loss of the Nd³⁺ sites and high covalency degree of the ligand field. The very high Ω₆ intensity parameter value makes evident both a great structural distortion of the Nd³⁺ sites and a strong electron–phonon coupling between Nd³⁺ and free OH⁻ ions, which is consistent with the phonon energy maximum (3442.1 cm⁻¹) recorded by Raman spectroscopy. This strong electron–phonon coupling favors high effective bandwidth and gain bandwidth values of the laser emission (⁴F_3/2 → ⁴I_11/2) of Nd³⁺ ions. The electric-dipole oscillator strengths of all the Nd³⁺ absorption transitions, and in particular that of the hypersensitive transition (⁴I_9/2 → ⁴G_5/2), are enhanced by this great structural distortion of the host. Broadband laser amplification of the ⁴F_3/2 → ⁴I_11/2 emission (1062 nm) of Nd³⁺ ions in the BBONd glass pumped at 805 nm (⁴I_9/2 → ⁴F_5/2 + ²H_9/2) is evaluated through the main fluorescent parameters in competition with non-radiative processes. In general, the BBONd glass exhibits spectroscopic parameters comparable with those reported in the literature for broadband laser amplification into the IR region.     

Photo-thermo-refractive glass co-doped with Nd as a new laser medium

Photo-thermo-refractive (PTR) glass demonstrates refractive index change after exposure to UV radiation followed by a thermal treatment that enables recording of high efficiency holographic optical elements. This work demonstrates feasibility of function of this material as a complex optical medium which posseses both photosensitive and luminescent properties and paves a way for creation of monolythic solid state lasers where resonator components can be holographically recorded inside of a laser medium. It was found, that incorporating of Nd³⁺ ions in PTR glass does not affect photosensitivity required for hologram recording. It was demonstrated that emission wavelength, spectral width, and cross section of Nd³⁺ luminescence in PTR glass are typical for silicate laser glasses and Nd-doped PTR glass can be considered as a promising laser medium for monolithic solid state lasers.     

Development of iridium TES by pulsed laser deposition with a Nd:YAG laser

The use of cryogenics micro calorimeters with Transition Edge Sensors for high-resolution spectroscopy for space applications puts several constraints on the detector's performances. Among several requirements, the long term stability of TES from a chemical and physical point of view is one of the most important. Iridium is a very interesting material for TES fabrication due to its excellent chemical stability and low transition temperature. Starting from the promising results we had with a cryogenic microcalorimeter with TES made of an Ir single crystal, we are developing a procedure to produce patterned Ir thin films by means of the Pulsed Laser Deposition (PLD). PLD with an infrared laser, in UHV, allows very clean evaporation process, good efficiency (about 4 nm/shot) and low dissipated power in the vacuum chamber (about 1 W). We have applied a lift-off mask technique that allows to heat the substrate during the deposition, which improves the adhesion and the thermal conductivity and circumvents the needs of very aggressive etchant solutions.     

Highly efficient diode-stack, end-pumped Nd:YAG slab laser with symmetrized beam quality

An efficient high-power cw Nd:YAG slab laser, partially end pumped by diode-laser stacks, and a novel beam-shaping technique are reported. The optical efficiency amounted to 44 %, and the slope efficiency amounted to 55 %. Introducing an intracavity Brewster plate to polarize the laser beam, we obtained an optical efficiency of 35 % and a slope efficiency of 41 %. The output beam was rectangular and the beam quality asymmetric in two orthogonal directions. To equalize the beam quality, we introduced a step-mirror beam-shaping technique. The beam-shaping technique and the results obtained are discussed.     

Trident: a versatile high-power Nd:glass laser facility for inertial confinement fusion experiments

The Trident Nd:glass laser system operates as an experimental facility supporting the national Inertial Confinement Fusion program at Los Alamos. The laser has two identical main beam lines with 14-cm-disk final amplifiers. The beams are frequency doubled, expanded to 19.2 cm, and focused on target with a variety of focusing optics. A third beam with 10-cm disk final amplifiers is also frequency doubled and used as a target-shooting or diagnostic beam simultaneously with the other two beams.

The facility provides a flexible combination of energy, pulse-shaping capabilities, and diagnostic tools for laser-target interaction experiments.

     

Performance of a prototype for a large-aperture multipass Nd:glass laser for inertial confinement fusion

The Beamlet is a single-beam prototype of future multibeam megajoule-class Nd:glass laser drivers for inertial confinement fusion. It uses a multipass main amplifier, adaptive optics, and efficient, high-fluence frequency conversion to the third harmonic. The Beamlet amplifier contains Brewster-angle glass slabs with a clear aperture of 39 cm x 39 cm and a full-aperture plasma-electrode Pockels cell switch. It has been successfully tested over a range of pulse lengths from 1-10 ns up to energies at 1.053 mum of 5.8 kJ at 1 ns and 17.3 kJ at 10 ns. A 39-actuator deformable mirror corrects the beam quality to a Strehl ratio of as much as 0.4. The 1.053-mum output has been converted to the third harmonic at efficiencies as high as 80% and fluences as high as 8.7 J/cm(2) for 3-ns pulses.