Ariel Bruner

Annular symmetry nonlinear frequency converters

We present a new type of two-dimensional nonlinear structure for quasi-phase matching. This structure has continuous rotational symmetry, and in contrary to the commonly used periodic structures, is not lattice shaped and has no translation symmetry. It is shown that this annular symmetry structure possesses interesting phase matching attributes that are significantly different than those of periodic structures. In particular, it enables simultaneous phase-matched frequency doubling of the same pump into several different directions. Moreover, it has extremely wide phase-mismatch tolerance, since a change in the phase matching conditions does not change the second harmonic power, but only changes its propagation direction. Several structures were fabricated using either the indirect e-beam method in LiNbO(3) or the electric field poling method in stoichiometric LiTaO(3), and their conversion efficiencies, as well as angular and thermal dependencies, were characterized by second harmonic generation.

Frequency stability at the kilohertz level of a rubidium-locked diode laser at 192.114 THz

The frequency stability of a 1560-nm diode laser, whose second harmonic was locked to (87)Rb sub-Doppler lines, was characterized by measuring the beat frequency relative to a 780-nm reference laser that was locked to sub-Doppler lines of another rubidium cell. The square root of the Allan variance reached a minimum value of 7.5 x 10(-12) in 1 s, which corresponded to frequency variations of 1.44 kHz for the 1560-nm laser. The frequency reproducibility of the system was approximately 1 x 10(-9). These values are better than those that can be achieved by locking to Doppler-broadened transitions at the 1550-nm wavelength band.

Second-harmonic generation of green light in periodically poled stoichiometric LiTaO3 doped with MgO

Periodically poled crystals of stoichiometric lithium tantalate doped with MgO (PP-Mg:SLT) were developed for a high-power optical frequency conversion. Inverted domain structures with 7.7μm period were fabricated in 1-mm-thick crystals by an electric-field poling using patterned metallic electrodes. Frequency-doubling characteristics of these units were investigated with continuous and pulsed Nd:YAG lasers. The nonlinear coefficient, d33, of Mg:SLT derived from these measurements is 13pm∕V, similar to that of the congruent lithium tantalate. A stable generation of 5.5W average power of green light at 532nm was obtained while the photoinduced breakdown of the periodically poled KTiOPO4 was observed under similar experimental conditions. These results demonstrate the advantage of Mg:SLT for high-average-power applications.

Frequency stabilization of a diode laser at 1540 nm by locking to sub-Doppler lines of potassium at 770 nm

An external cavity 1540-nm diode laser was frequency doubled in a 3-cm-long periodically poled LiNbO(3) waveguide doubler with 150% W(-1) conversion efficiency, thereby generating more than 3 muW at 770 nm. Second-harmonic light was used to detect and lock to sub-Doppler lines of the (39)K D(1) transition.

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.

Refractive index dispersion measurements of congruent and stoichiometric LiTaO 3

We present a temperature-dependent Sellmeier equation for congruent and stoichiometric LiTaO3. The refractive indices in the range of 0.39-4.1 micrometers were determined by scanning the pump lasers wavelength and finding the QPM second harmonic wavelength for a series of period- temperature pairs, and from QPM OPO measurements. The obtained new Sellmeier coefficients were used to calculate the QPM wavelengths of the idler and signal for a PPSLT OPO pumped at 1064 nm. An OPO based on PPSLT was demonstrated. The idler-tuning range was 4.1828-3.9898 micrometers for temperatures of 40-200 degree(s)C. The obtained wavelengths were in good agreement with our predictions.

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.

Distinct distances between a collinear set and an arbitrary set of points

Abstract We consider the number of distinct distances between two finite sets of points in R k , for any constant dimension k ≥ 2 , where one set P 1 consists of n points on a line l , and the other set P 2 consists of m arbitrary points, such that no hyperplane orthogonal to l and no hypercylinder having l as its axis contains more than O ( 1 ) points of P 2 . The number of distinct distances between P 1 and P 2 is then Ω min n 2 ∕ 3 m 2 ∕ 3 , n 10 ∕ 11 m 4 ∕ 11 log 2 ∕ 11 m , n 2 , m 2 . Without the assumption on P 2 , there exist sets P 1 , P 2 as above, with only O ( m + n ) distinct distances between them.

All-Fused-Silica Technology for On-Chip High Power Applications

Silica-on-Silica technology enables fabrication of waveguide-based on-chip devices for high-power applications. We demonstrate a 25µm thick Yb/Al-codoped fused silica slab waveguide with 0.2dB/cm loss and 0.6dB/cm gain, and a 25X25µm all-fused-silica rectangular waveguide.