OptiCall Software (Sweden)

We report on efficient intracavity frequency doubling of a cw diode-pumped Nd:YAG laser on the (4)F(3/2)?(4)I(9/2) laser transition at 946 nm. The nonlinear crystal used in the experiments was a first-order quasi-phase-matched flux-grown KTiOPO(4) crystal (period, 6.09mum ; thickness, 1 mm; length, 9 mm). The fluctuations in the generated second-harmonic wave were lower than 3% at output powers of as much as 500 mW. The overall optical-to-optical efficiency was 5.7%. A maximum output power of 740 mW of blue light was generated, which was stable for only 0.5 min. The decrease the output power at this power level was attributed to heating and thermal lensing in the periodically poled KTiOPO(4) crystal. The short-term behavior of the second-harmonic wave exhibited switching between a cw mode and chaotic intensity fluctuations.

The prevailing technique for assessing surface roughness and related parameters from engineering surfaces in industry is mechanical stylus profilometry. Though it is a conceptually direct method it suffers from several drawbacks; the measurement is not area-covering while many important features of engineering surfaces are related to 3D topography; the technique is slow; and, the technique involves contact with the surface, potentially damaging it. For surfaces of optical quality, elastic light scattering provides an efficient way of characterizing surfaces, and two ASTM standards exist pertaining to such measurements. However, the theoretical models based on first order perturbation theory break down when the rms roughness approaches one tenth of the incident wavelength. We have used infrared scattering at 10.6 micrometers wavelength to provide area-covering, non-contact surface characterization of engineering surfaces. The surface power spectral density is calculated from the scattering distribution by Rayleigh-Rice vector perturbation theory. Measurement of bandwidth limited surface roughness is demonstrated for ground and polished surfaces in the root mean square roughness range of 0.03 micrometers to 1.7 micrometers . Good correlation with contact stylus measurements is achieved for nearly 1D surfaces, anisotropic surfaces, and isotropic surfaces. Measurement of scratch and lay characteristics are also demonstrated.

Experimental investigations of electron relaxation in the confinement region and capture into the quantum wells are reported for InGaAsP/InP laser structures. The measurements are performed by time-resolved photoluminescence using upconversion. The value for the electron capture of 1.4 ps is obtained. No dependence on the potential profile of confining layers has been observed.

We have developed and demonstrated a novel technique to manufacture very long and superstructured gratings based on writing a set of consecutive subgratings with interferometric control of the relative position between the subgratings.

Space-charge-induced optical nonlinearities for asymmetric coupled quantum wells have been studied. Calculations for optimized AlGaAs structures show that a blue-shift of the band gap of 9 meV at a carrier density of 1012 cm-2 can be obtained. Experimental comparisons with a rectangular well show a large increase in room-temperature nonlinearities.

Use of integrated optical waveguides is advantageous for frequency conversion of light from low-power lasers. The light can be confined to a very small cross section area for a comparatively long distance so that high conversion efficiencies can be obtained with pump sources such as laser diodes and laser diode pumped solid state lasers.

Generation of blue light from small solid-state light sources is a technological challenge with applications in many areas, among others optical data storage. The authors report frequency doubling using third-order quasi-phase matching in periodically domain-inverted lithium tantalate waveguides. Periodic proton exchange followed by heat treatment caused periodic domain inversion and waveguide formation in a single step. Infrared radiation from a dye laser was coupled through the waveguides and second-harmonic generation corresponding to third-order quasi-phase-matching was observed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Recently there has been a great interest in quasiphase-matching (QPM) waveguides for frequency conversion. Such waveguides have been fabricated in lithium niobate, lithium tantalate, KTP, and organic materials. In LiNbO3 and LiTaO3 a number of different fabrication techniques have been employed to obtain the required periodic reversal of the ferroelectric domain orientation. We have demonstrated generation of blue light by frequency doubling in QPM waveguides, fabricated in LiNbO3 as well as in LiTaO3. In the latter case, domain inversion was obtained by proton exchange in combination with a heat treatment. We now report on a comparison, based on simulations and experiments, between these two types of QPM waveguide. For the LiTaO3 the domain inverted regions show an approximately semicircular cross-section, compared with a more triangularly shaped cross-section in LiNbO3 more promising for a high conversion efficiency. In particular it should be more easy in LiTaO3 to come close to the theoretical limit when using third-order quasiphase matching. To utilize the possibility of a more efficient interaction by going to first-order QPM, it is, however, critically important to obtain a very tight mode confinement. It is also concluded that the duty cycle is an essential parameter to optimize.

Several materials and methods are investigated in the search for devices for efficient frequency doubling of infra-red diode lasers to blue. Such compact light sources would find important applications in i.e. optical data storage, displays and spectroscopy.