V. Magni

Solid-state laser unstable resonators with tapered reflectivity mirrors: the super-Gaussian approach

A general procedure for treating solid-state laser unstable resonators with tapered reflectivity mirrors within the framework of geometrical optics is presented. A suitable choice of the analytical form of the reflectivity profile, which can simulate many experimental devices, makes possible the derivation of simple design equations for the resonator parameters. Experiments performed with a pulsed Nd:YAG laser containing a variable-reflectivity output coupler, implemented with vacuum evaporation techniques, are discussed. >

High-power diffraction-limited Nd:YVO/sub 4/ continuous-wave lasers at 1.34 /spl mu/m

We describe the development of Nd:YVO/sub 4/ lasers with continuous-wave emission at 1.342 /spl mu/m; they contain either one or two crystals which are longitudinally pumped by fiber-coupled diode laser arrays. With a single crystal, the output power is 7.3 W, while with the twin crystal configuration the power reaches 12 W. The best slope efficiency is 40% and the output beam divergence is about two times the diffraction limit. The influence of the Nd concentration, of the pump spot-size, and of the resonator configuration have been experimentally studied. Data on the thermally induced lens are also reported and discussed.

Radially variable reflectivity output coupler of novel design for unstable resonators

An output coupler with radially variable reflectivity, based on a Fabry-Perot interferometer made of two suitable spherical mirrors, is proposed. Application to a pulsed Nd:YAG laser with an unstable resonator has produced diffraction-limited output beams with energy up to 300 mJ.

Optical coatings with variable reflectance for laser mirrors.

Design procedures and fabrication techniques of variable reflectance dielectric mirrors for laser output couplers are proposed. The design criteria, based on the use of only one shaped layer in a multilayer structure, yield any peak value and shape of the reflectance profile. The deposition technique of the variable thickness layer consists of a sputtering process with a suitable mask interposed between the target and substrate. Results of a simple model that correlates the mirror parameters to mask diameter and position are presented. A few devices for a Nd:YAG laser have been proposed, characterized, and successfully tested in a laser resonator.

Mode locking by cascading of second-order nonlinearities

We present a comprehensive theoretical and experimental study on a new passive mode-locking technique, called cascaded second-order nonlinearity mode locking (CSM), which exploits cascaded second-order nonlinearities to obtain large third-order susceptibilities from an intracavity second harmonic crystal. The nonlinear phase shift that originates in the nonlinear crystal is converted into a nonlinear amplitude modulation by a suitable intracavity aperture. A numerical model, based on a perturbative approach, allows the nonlinear loss modulation of resonators used for CSM to be calculated as a function of the resonator parameters and of the phase mismatch. The predictions of the model are confirmed by experiments performed on a CW Nd:YAG laser. The effects of group velocity mismatch and the limitations which it poses on the minimum achievable pulsewidth are analyzed both experimentally and theoretically.

Pump power stability range of single-mode solid-state lasers with rod thermal lensing

The pump power stability range of solid-state laser resonators operating in the TEM 00 mode has been thoroughly investigated. It has been shown that, for a very general resonator containing intracavity optical systems, rod thermal lensing engenders a pump power stability range which is a characteristic parameter of laser material and pump cavity, but is independent of resonator configuration. Stability ranges have been calculated and critically discussed for Nd:YAG, Nd:glasses, Nd: Cr: GSGG, and alexandrite. The independence of the pump power stability range from the resonator configuration has been experimentally demonstrated for a CW Nd:YAG laser.

Optimum beams for efficient frequency mixing in crystals with second order nonlinearity

Abstract The problem of finding the optical beams that generate the sum or difference frequency with the greatest possible efficiency in homogeneous crystals with second order nonlinearity is tackled and solved. The interacting beams are first represented as combinations of Laguerre–Gauss modes, and the values of the expansion coefficients are then numerically calculated to determine the most efficient beam shapes and the phase matching condition, neglecting the power depletion of the two pump beams. Some numerical examples of practical relevance, including second and third harmonic generations, are discussed, and it is shown that the absolute maximum of efficiency is in general only slightly greater than that obtainable with suitably focused Gaussian beams.

Thyratron‐switched N2 atmospheric‐pressure oscillator, low‐pressure amplifier laser system

The article presents the results of experimental investigation on an atmospheric‐pressure N2 oscillator low‐pressure N2 amplifier system. This system gives pulses of a duration of about 0.8 ns, with 800‐kW peak power, and good (±3%) stability. The parameters affecting the oscillator–amplifier operation are discussed with the aim of optimizing system performances.

Rod thermal lensing effects in solid-state laser ring resonators

Abstract A comprehensive analysis of the effects of thermal focusing of the rod in stable ring resonators containing arbitrary intracavity optical systems is presented. The resonator stability, the mode spot size, the dynamical stability and the sensitivity to misalignment are investigated and a few basic properties are stated. This analysis might constitute a basis for improving the design of single transverse mode solid state lasers.

Optimization study of a picosecond rotating-mirror autocorrelator

Abstract A few geometrical-optic properties of a reflecting dihedron made by a mirror pair are discussed in order to find an optimized configuration for a rotating mirror autocorrelator. It is shown that there does exist such a configuration, which maximizes the scanning range and minimizes the non-linearity error. Based on this scheme, a low-cost, dispersion-free autocorrelator has been made, whose linearity is better than 2% over a scanning range of 500 ps.