Mordechai Katz

Broadly tunable dual-wavelength light source for coherent anti-Stokes Raman scattering microscopy

The signal and idler beams from a picosecond, synchronously pumped optical parametric oscillator (OPO) provide the two colors necessary for coherent anti-Stokes Raman scattering (CARS) microscopy. The OPO provides a continuously tunable frequency difference between the two beams over a broad range of Raman shifts (100-3700 cm(-1)) by varying the temperature of a single nonlinear crystal. The near-infrared output (900-1300 nm) allows for deep penetration into thick samples and reduced nonlinear photodamage. Applications of this light source to in vivo cell and ex vivo tissue imaging are demonstrated.

Low temperature periodic electrical poling of flux-grown KTiOPO4 and isomorphic crystals

Studies of dielectric spectroscopy, dc conductivity, and polarization switching allowed the observation of phase transition from the superionic to the insulating state in flux-grown KTiOPO4 (KTP) crystals at low temperature where the high mobility of potassium ions is suppressed. A low temperature method of fabrication of engineered periodic domain structures in superionic KTP and isomorphic crystals is proposed. It enabled us to tailor homogeneous domain gratings with various periods in the range 4–39 μm for quasiphase-matched nonlinear optical converters in KTP plates over whole area of 30×30 mm2.

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 blue light generation in KTiOPO4 waveguides

Very high normalized efficiency, up to 800% W−1 cm−2 for infrared to blue light conversion (425 nm), has been obtained in quasi‐phase‐matched waveguides in KTiOPO4. It is shown by a detailed calculation that this value is higher by a factor of 4 than that predicted by theory.

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% W−1 cm−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 soliton self-reflection at a quadratically nonlinear interface.

The reflection of bulk quadratic solutions incident onto a quadratically nonlinear interface in periodically poled potassium titanyl phosphate was observed. The interface consisted of the boundary between two quasi-phase-matched regions displaced from each other by a half-period. At high intensities and small angles of incidence the soliton is reflected.

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.

Properties of quadratic multi-soliton generation near phase-match in periodically poled potassium titanyl phosphate

The properties of the multi-quadratic-soliton generation process have been investigated both theoretically and experimentally near and on phase-match in non-critically-phase-matched, periodically poled, potassium titanyl phosphate (PPKTP). It was found that multi-soliton generation occurs primarily due to asymmetry in the input beam and at phase-matching. The number of solitons generated depended on the input intensity in a non-trivial way.

Weak beam control of multiple quadratic soliton generation

Theoretical predictions and experimental observations show that a weak harmonic seed beam can control the process of generating multiple quadratic solitons in periodically poled KTiOPO4 by inputting only a fundamental beam. This all-optical switching does not depend on the relative phase of the input beams, an unusual property for such coherent solitons.

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.