D. Eger

Nondestructive imaging and characterization of ferroelectric domains in periodically poled crystals

We report the nondestructive investigation and visualization of periodically poled domains in ferroelectric potassium titanyl phosphate (KTP) crystals using polarization sensitive scanning force microscopy (SFM). Applying an alternating voltage technique to SFM allows ferroelectric domain wall resolution beyond 100 nm. Image contrast between KTP and Rb doped KTP, i.e., rubidium titanyl phosphate (RTP) regions arises from the differential piezoelectric response. We find the polarization vectors in both KTP and RTP to be aligned parallel to the negative z axes as deduced (a) when comparing our data with a ferroelectric reference sample, i.e., tri-glycine sulfate (b) from comparison of nanoscale hysteresis loops recorded on KTP and RTP, and (c) from direct domain switching in KTP applying very high electric fields between tip and counter electrode. The latter experiments show that nanoscale ferroelectric domains in KTP switch from the negative to the positive z-axes alignment for electric fields stronger tha...

Highly efficient doubling of a high-repetition-rate diode-pumped laser with bulk periodically poled KTP.

An internal doubling efficiency of 64% at 2 MW/cm(2)was obtained in a single-pass configuration with an uncoated, 1-cm-long, bulk periodically poled KTP crystal placed outside the resonator of a pulsed, diode-pumped Nd:YAG laser. An average of 4.8W of green light was obtained from a 7.5-W pump beam inside the crystal. Doubling efficiency exceeded 50% at levels of 0.75 MW/cm(2). The measured thermal tolerance of the doubling process (FWHM) was 3.3( degrees )C cm, and the measured temperature tuning coefficient was 0.053 nm/( degrees )C .

Efficient resonant frequency doubling of a cw Nd:YAG laser in bulk periodically poled KTiOPO(4).

A cw Nd:YAG laser was quasi-phase-matched frequency doubled by a bulk periodically poled flux-grown KTiOPO(4) crystal in an external resonant cavity. The conversion efficiency and the second-harmonic power with a pump of 225 mW were 55% and 123.5 mW, respectively. The loss of the 1-cm-long crystal, which operated near room temperature, was 1.3% and was dominated by scatter from the cleaved facets of the crystal. No damage, photorefractive or other, was observed at intensites of 370Wmm(-2) , but beam size had to be optimized to eliminate thermal-induced instabilities in the doubling cavity.

Optical characterization of KTiOPO4 periodically segmented waveguides for second‐harmonic generation of blue light

Periodically segmented waveguides were fabricated by the ion exchange process in KTiOPO4. The waveguides were characterized by measuring the spectra of the transmitted and reflected guided infrared light and of the second‐harmonic‐generated power. The near‐field distribution of the fundamental and second‐harmonic wave was also investigated. Infrared to blue light conversion efficiency up to 250%u2009W−1u2009cm−2 was obtained. Waveguide characteristics were calculated by replacing the segmented structure with an equivalent continuous waveguide. Good agreement between the calculated and measured values was obtained.

Quadratic spatial solitons in periodically poled KTiOPO4

The evolution of fundamental beams into quadratic spatial solitons was investigated in a periodically poled bulk KTiOPO4 crystal near and at phase matching. Various soliton properties, such as trapping efficiency as a function of phase mismatch, poling-induced walk-off, and the effects of pulse width, beam width, and input beam quality, were measured. Effects attributed to the presence of cubic nonlinearities were also observed.

Second-harmonic generation in Bragg-resonant quasi-phase-matched periodically segmented waveguides

Second-harmonic generation in Bragg-resonant quasi-phase-matched periodically segmented waveguides is studied experimentally and theoretically. At resonance, a deep spectral valley appears in the quasi-phase-matching curve. Nevertheless, in practice, the conversion efficiency is significant, in spite of this effect, because of reduced reflections, especially at 2omega. The mechanism behind this reduction seems to be small random variation in the location and shape of the domain boundaries.

Refractive dispersion curve measurement of KTiOPO4 using periodically segmented waveguides and periodically poled crystals

We introduce a technique for measuring the refractive indices of a crystal and apply it to measure the dispersion curve of KTiOPO4. The refractive index evaluation is based on measurement of the Bragg reflection wavelength of periodically segmented waveguides close to cut-off conditions. The measurement error is found to be less than 10−4. Second harmonic generation and optical parametric oscillation in periodically poled KTiOPO4 enable us to extend the measurement to a wide wavelength range. A room temperature Sellmeier type equation for the dispersion curve nz(λ) of flux-grown KTiOPO4 in the entire transparency range of the crystal is determined.

Bragg reflection in periodically segmented KTiOPO4 waveguides

Distributed Bragg reflection spectra in segmented waveguides of KTiOPO4 are studied both theoretically and experimentally. Regular period and super period structures are analyzed. The reflectivity is found to be strongly dependent on the unit cell structure. High reflectivity values, in excess of 90%, are obtained in relatively short 3.8 mm waveguides.

Efficient frequency doubling and locking of diode laser light in periodically segmented KTiOPO4 waveguide

Simultaneous frequency doubling and Bragg reflection locking of the light of a GaAlAs diode laser was obtained by two separate sections of a periodically segmented waveguide of KTiOPO4. A blue light power of 3.6 mW at 429 nm was generated. The blue light was emitted in a circular beam with a low divergence angle of 5.7°.

Second harmonic generation tuning curves in quasiphase-matched potassium titanyl phosphate with narrow, high-intensity beams

The second harmonic generation (SHG) tuning curves with temperature and angle of incidence were measured in periodically poled KTiOPO4 for narrow fundamental beams at intensities typical of quadratic soliton generation. Mutual self-focusing of the fundamental and harmonic, cascading, and walk-off for light incidence away from the poling axis drastically distorted the SHG response curves, in good agreement with theory.