Abraham Englander

Periodically poled KTiOAsO4 crystals for optical parametric oscillation

Polarization switching and dielectric spectroscopy of KTiOAsO4 (KTA) crystals have been studied. This has allowed, for the first time, the fabrication by low temperature poling of periodically-poled domain structures in KTA crystals (0.5 mm thick, 10 mm long) and also the observation of optical parametric oscillation in the mid-infrared region. The integrity of the periodic domain pattern and the structural perfection of the periodically poled crystal have been demonstrated using scanning electron microscopy (SEM) and high-resolution x-ray diffraction imaging.

Generation of a high-energy ultrawideband chirped source in periodically poled LiTaO3

A method for generation of a chirped, ultrawideband infrared source by use of optical parametric generation in periodically poled crystals and pumped by a chirped Ti:sapphire laser is described. A ∼35% bandwidth in the idler branch was demonstrated in a periodically poled LiTaO3 crystal pumped by a chirped Ti:sapphire laser with 2.1% bandwidth. Optical parametric generation and optical parametric amplification configuration allowed us to generate up to a ∼250-µJ chirped pulse from 2.1 to 3 µm.

Average power effects in periodically poled crystals

The introduction of periodically poled crystals with high non-linear coefficients has lowered significantly the threshold for parametric processes. This progress enables pumping frequency conversion devices with low pulse energy, Q-switched, diode-pumped, solid-state lasers. New non-linear optical ferroelectric materials, such as KTP and Stoichiometric Lithium Tantalate (SLT) were proven to exhibit adequate deff, higher optical damage resistance and lower photo-refractivity in comparison to well-known periodically poled Lithium Niobate. Advances in poling technology have enabled the production of relatively thick periodically poled crystals from those materials. Thus, in principal much higher average power levels can be converted. We have investigated the effects that limit frequency conversion efficiency as power levels are increased. Average power induced thermal lensing and thermal phase mismatching were considered. The resulting power limitations are discussed, and under some assumptions quantitative expressions for these limits were formulated. Thermal lensing imposes a limit on the local power density. Thermal phase mismatching imposes a limit on the overall power.

Periodically poled thick wafers of near stoichiometric LiTaO 3

Near stoichiometric LiTaO3 is investigated for high power quasi-phase-matched optical frequency conversion applications due to its high optical damage threshold and low coercive field. In this work, near stoichiometric undoped and MgO-doped LiTaO3 wafers were characterized by transmission through cross-polarizes, x-ray diffraction and microscope inspection. Periodically inverted domain structures were fabricated in 1 to 4mm thick wafers, by electric field poling in vacuum. Efficiency values between 10% and 16% were obtained for direct frequency conversion of 1 μm to 4 μm light using optical parametric oscillations scheme. The resulting periodically poled structure quality and frequency conversion efficiency seems to be limited by crystalline imperfections of the wafers.

Doubling the frequency of depleted fundamental waves in periodically poled KTiOPO4

Frequency doubling of a diode-pumped Nd:YAG laser in 1 and 2 cm long periodically poled KTiOPO4 wafers has been investigated. Up to 60% doubling efficiency has been achieved. The good agreement obtained between measured results and those calculated by numerical integration of the coupled wave equations demonstrate that the efficiency is limited by the basic process of backconversion and dephasing rather than by thermal effects.

Frequency conversion efficiency limitation in periodically poled KTP crystals and waveguides

Frequency conversion efficiency limiting factors in PPKTP crystals and segmented waveguides have been investigated. It was found that at high intensity, back conversion effects related to the spectral and spatial properties of the laser beam, limit the conversion efficiency. High conversion efficiencies in PPKTP are demonstrated by selecting proper laser conditions. A parametric study of the influence of geometrical parameters on conversion efficiency in periodically segmented waveguides has been carried out and an optimal design parameter range has been defined. An improved waveguide structure in which higher efficiencies can be obtained is suggested.

Frequency doubling in periodically poled flux-grown KTP of short period length

Periodically poled KTiOPO4 (KTP) wafers with short period length are required for generation of green and blue coherent light. Electric field poling processes developed for producing inverted micrometer scale domain structures in other ferro-electric materials cannot be directly applied to flux-grown KTP due to its relatively high (super ionic) conductivity at room temperature. In this paper we describe the low temperature method developed by us for poling flux- grown KTP crystals without modifying their composition. High voltage switching pulses were applied to KTP samples at a temperature below the superionic insulating transition and the switching charge was continuously monitored. This way, high quality domain gratings of 3.8 - 10 micrometers periods were fabricated in 0.5 - 1.0 mm thick flux-grown KTP plates. Second harmonic generation in the range of 400 - 530 nm light by these samples were tested with different types of IR lasers including diode, diode pumped solid state and fiber lasers. The results demonstrate that the low temperature poling technique can provide high quality, short period periodically poled KTP for blue and green coherent light generation.

Generation of ultrawide-band chirped sources in the infrared through parametric interactions in periodically poled crystals

A method to generate chirped ultrawide-band sources with a chirp bandwidth of about 50% in the infrared is described and experimentally verified. It is based on optical parametric generation in periodically poled crystals with a chirped Ti:sapphire as a pump source. We have demonstrated a 27% wide bandwidth in the signal branch and 45% bandwidth in the idler branch when a periodically poled KTP crystal was pumped by a chirped Ti:sapphire laser with 12 nm full width at half maximum bandwidth.

Generation of a High-Energy Ultra-Wideband Chirped Source in Periodically Poled Crystals

A method to generate chirped, ultra-wideband infrared source, by use of optical parametric generation in periodically poled crystals, pumped by a chirped Ti:sapphire, laser is described. Few hundredth of micro-Joule were measured.

Efficient high power eye-safe opo with pp-ktp

Optimization studies of an eye-safe PP-KTP OPO were conducted. A 50% signal conversion efficiency with a 28 mm long crystal and more than 2 Watt average power in a signal resonating SRO were achieved.