O. Pacaud

Widely and continuously tunable optical parametric oscillator based on a cylindrical periodically poled KTiOPO 4 crystal

We report on what is to our knowledge the first realization of a quasi-phase-matched optical parametric oscillator (OPO) based on a crystal with a cylindrical shape. The main reason for interest in this device is its broad, continuous tuning. In experiments with a 1064-nm pump, the signal tuning range was equal to 525 nm (1515-2040 nm), and the corresponding idler was continuously tuned over 1340 nm (2220-3560 nm). The angular tuning was 26 degrees , with only a minor variation of the OPO threshold over the entire tuning range.

Crystal growth and refined Sellmeier equations over the complete transparency range of RbTiOPO4

Abstract The phase-matching directions sum- and difference-frequency generations are measured in the principal planes of RbTiOPO 4 crystals grown from a halide flux. The use of crystals with a cylindrical shape and of a tunable laser source allows us to perform accurate measurements over the complete transparency range of that material, and to determine a refined set of Sellmeier equations valid for any phase-matched interaction in that crystal.

Cylindrical KTiOPO 4 crystal for enhanced angular tunability of phase-matched optical parametric oscillators

We demonstrate what is to our knowledge the first optical parametric oscillator (OPO) based on a cylindrical phase-matched nonlinear crystal. Experiments are performed with an uncoated KTiOPO(4) crystal cut as a cylinder with a diameter of 21.2 mm and a thickness of 5 mm. We achieve 20.5-internal-degree angular tuning in a 1064-nm-pumped type III OPO, which would correspond to ~36 degrees external angular rotation for a parallelepipedal crystal. The goals of using such a device are to narrow the spectral width of the output and to enhance the spatial quality of the generated beams in widely tunable OPOs.

Tunable phase-matched optical parametric oscillators based on a cylindrical crystal

The use of cylindrical nonlinear crystals is a good way to extend the angular-tuning capability of optical parametric oscillators. We consider the example of a 1064-nm-pumped KTiOPO4 optical parametric oscillator phase matched in the x–z plane. A 31.5° angular tuning is demonstrated, limited by the spectral range of the mirrors. The measured slope efficiency and threshold energy are compared with the values published for a similar optical parametric oscillator that uses a parallelepipedic crystal. We study the beam quality of the emitted signal. The experiments with a plano–plano cavity point out the spatial-filtering effect due to the short focal length of the cylindrical crystal placed in the cavity. A simple model based on the coupling of the pump and the signal Gaussian beams in the cavity is developed. We then investigate the respective effects of the different experimental parameters on the output beam quality: radius of curvature of the mirrors, cavity length, crystal radius, pump-beam waist size, and spectral-tuning range of the signal beam. These calculations lead to the definition of the optimum configuration associated with a low M2 independent of the emitted wavelength. An experimental demonstration of that solution is given with excellent results: M2<1.5 is obtained, constant over 9° angular tuning.

Extended sphere method for complete investigation of the phase-matching properties of sum- and difference-frequency generation

We demonstrate the feasibility of a complete experimental investigation of the phase-matching properties of sum- and difference-frequency generation in a single crystal cut as a sphere over its entire transparency range. The class of the studied crystal is the only initial data that is required. This feasibility study was carried out with rubidium titanyl arsenate.

Mid-infrared laser source with high average power and high repetition rate

An amplified passively Q-switched laser at 35kHz pumps an optical parametric generator to generate 1.5W around 1.5μm. Proper control of thermal lensing due to absorption of idler beam is critical for power scaling.

High Repetition Rate, High Average Power, Mid-Infrared Laser

An optical parametric generator pumped by an amplified passively Q-switched laser at 35kHz generates 1.5W around 1.5µm. Management of thermal lensing due to residual absorption of idler beam is critical for power scalability

Continuously tunable optical parametric generator using a cylindrical ppLN

An optical parametric generator using a cylindrical ppLN crystal pumped by a Nd:YAG microchip laser leads to continuously tunable (1420nm-1700nm and 2800nm-4200nm) highly efficient (30%), low divergent, compact and stable device.

Optimization of the cavity geometry in tunable optical parametric oscillators based on cylindrical crystals

Summary form only given. Optical parametric oscillators based on a cylindrical crystal have been realized recently, following the set-up where the cylinder axis is orthogonal to the cavity optical axis and to the plane containing the useful phase-matching directions. The interacting beams always propagate at normal incidence, leading to a broad angular tunability. The present study is devoted to the beam quality of the emitted signal. We demonstrate that the geometry of the KTP crystal is responsible for a spatial filtering effect which can result in a low M/sup 2/, independent on the spectral tuning of the OPO. We investigate the variation of the beam quality with respect to the different geometrical parameters: cavity length and radius of curvature of the mirrors, crystal diameter, pump beam waist size, and spectral range of the generated signal. These calculations, based on a simple gaussian beam model, allow us to define the most suitable operating conditions corresponding to a good and constant beam quality over a maximum spectral tuning.

Refined Sellmeier equations from phase-matching measurements over the complete transparency range of KTiOAsO 4 , RbTiOAsO 4 and CsTioAsO 4 .

Sum- and difference- frequency generation phasematching properties are measured in spheres of KTiOAsO4, RbTiOAsO4 and CsTiOAsO4 for Sellmeier equations refinement over their complete transparency range.