H. Karlsson

Transmission measurements in KTP and isomorphic compounds

The optical biaxial nature of crystals in the potassium titanyl phosphate (KTP) family result in anisotropic transmission that depends on the polarization direction of the transmitted radiation with respect to the fundamental crystal axes. Knowledge of the polarization-dependent crystal transmission is important for all wavelength-conversion applications and in particular is the only limitation on possible combinations of wavelengths when one uses the quasi-phase-matching techniques recently developed for the KTP family materials. In this study, polarized transmission spectra of KTiOPO(4) (KTP), RbTiOPO(4), RbTiOAsO(4) (RTA), and KTiOAsO(4) were measured over the 0.3-6-mum wavelength range with a spectrophotometer and a Fourier-transform infrared spectrometer. Seven crystal samples were studied, including four samples of KTP crystals of different origins. Variations in spectral transmission on the short- and long-wavelength edges, as well as visible-wavelength transmission and OH(-) absorption properties, are presented and discussed. The transmission of one sample of KTP and of RTA was also measured before and after periodic electric field poling.

Nanoscale imaging of domains and domain walls in periodically poled ferroelectrics using atomic force microscopy

We use the inverse piezoelectric effect for high-resolution imaging of artificially produced ferroelectric domains in periodically poled potassium titanium phosphate, KTiOPO4, and lithium niobate, ...

Periodic poling of RbTiOPO4 for quasi-phase matched blue light generation

RbTiOPO4 has been periodically poled for first-order quasi-phase matching. The poling was monitored using a technique based on the electro-optic effect, which enabled fabrication of high-quality domain gratings for efficient frequency doubling to the blue.

Second-harmonic imaging of ferroelectric domain walls

Domain walls in periodically poled ferroelectric KTiOPO4 and LiNbO3 crystals are observed by making use of second-harmonic (SH) generation enhancement in the transition regions between neighboring domains. SH images of domain walls obtained with various samples for different polarization configurations are presented. The SH generation enhancement is found especially pronounced for the polarization of the SH radiation being perpendicular to the domain walls. The origin and selection rules for the contrast in SH images of domain walls are discussed. The results obtained suggest that the domain walls produce a deteriorating effect on SH generation by quasiphase matching.

Real-time and in situ monitoring of ferroelectric domains during periodic electric field poling of KTiOPO4

We demonstrate a photographic method to view the inversion of ferroelectric domains during the periodic electric field poling of KTiOPO4 by taking advantage of the electro-optic effect and a high speed charge coupled device (CCD) camera. The method is noninvasive and allows monitoring in situ and in real time. The high speed CCD camera opens up the possibility to observe the dynamics of the domains during poling and to probe the samples afterwards to evaluate the grating formed in the material. This monitoring method should be applicable to other ferroelectric crystals, as well.

Efficient Nd:YAG Laser Frequency Doubling with Periodically Poled KTP.

Periodically poled flux-grown KTiOPO(4) was used for efficient extracavity 1064-nm Nd:YAG laser frequency doubling. A conversion efficiency exceeding 65% was obtained in Q-switched operation, and 1.34 W of average frequency-doubled power was generated with 2.2 W of mode-locked laser output. The conversion efficiency is approximately two times higher for periodically poled KTP than for conventional type II phase-matched KTP. The measurements indicate that periodically poled KTP is less susceptible to optical damage than type II KTP.

Efficient frequency doubling of a vertical-extended-cavity surface-emitting laser diode by use of a periodically poled KTP crystal

Blue light with a cw power in excess of 42 mW is generated from a frequency-doubled, extended-cavity InGaAs/GaAs 980-nm surface-emitting laser by use of a periodically poled KTP crystal.

High-power optical parametric oscillation in large-aperture periodically poled KTiOPO(4).

Electric field poling has been employed to fabricate 3-mm-thick periodically poled KTiOPO>(4) crystal for a high-power optical parametric oscillator. The maximum output power of the singly resonant optical parametric oscillator reached 13 mJ with 45% efficiency when the resonator was pumped with a 2.2-mm-diameter beam from a Q-switched Nd:YAG laser. The influence of the cavity design on the spectral and spatial qualities of the output parametric radiation is also discussed.

Broadly tunable infrared femtosecond optical parametric oscillator based on periodically poled RbTiOAsO 4

We present results from what we believe is the first reported example of an optical parametric oscillator based on periodically poled RbTiOAsO(4). The oscillator is pumped by a femtosecond self-mode-locked Ti:sapphire laser and, with a single-grating 2-mm-long crystal and one mirror set, a combination of pump and cavity-length tuning provided wavelength coverage from 1060 to 1225nm (signal) and 2.67 to 4.5 microm (idler). Average output powers were as much as 120mW in the signal and 105mW in the idler and interferometric autocorrelations recorded at signal and idler wavelengths of 1.1 and 3.26 microm, respectively, imply pulse durations of 125 and 115fs, respectively.

First-order type II quasi-phase-matched UV generation in periodically poled KTP

Type II quasi-phase matching was employed for first-order frequency doubling of a single-longitudinal-mode Ti:sapphire laser in periodically poled KTP with a domain-inverted period of 9.01 mum . In a single-pass configuration, 0.44 mW of UV power at 398.8 nm was generated for an input of 780 mW, corresponding to a normalized conversion efficiency of 0.09%W(-1) cm(-1) . The nonlinear coefficient d(24) = 2.82 pm/V was deduced from the measurements. The larger grating period for the type II quasi-phase-matched second-harmonic-generation process than for type I quasi-phase matching, lowers the fabrication constrains in the short-wavelength region and increases the acceptance bandwidth.