Hidenobu Ono

Group-velocity-matched noncollinear second-harmonic generation in quasi-phase matching

We demonstrate group-velocity-matched second-harmonic generation of 80-fs pulses under noncollinear quasi-phase-matching (QPM) geometry. Second-harmonic pulses of 100-fs duration, 11-nm bandwidth, and0.78-µm center wavelength were generated with 50% efficiency with 3-mm-long periodically poled lithium niobate. We have also numerically studied the dependence of conversion efficiency and pulse durations on pump intensity, propagation length, and noncollinear angle. It is confirmed that our group-velocity-matching scheme requires a much lower pump intensity than the conventional collinear QPM scheme.

Cascaded third-harmonic generation of ultrashort optical pulses in two-dimensional quasi-phase-matching gratings

Cascaded third-harmonic generation (THG) of femtosecond pulses in a two-dimensional periodically poled lithium niobate is demonstrated experimentally. The poling pattern satisfies quasi-phase-matching conditions for both second-harmonic generation (SHG) and the following sum-frequency generation. The pulse-front tilt in noncollinear interactions compensates for group-velocity mismatch among fundamental, second-harmonic (SH), and third-harmonic (TH) pulses, thereby achieving broad acceptance bandwidths in SHG and THG. A 2 mm thick device generates SH and TH pulses of 106 and 110 fs, respectively, from fundamental pulses with temporal duration of 118fs and a 1568 nm center wavelength. The frequency conversion properties are studied theoretically, and the optimal focusing condition for maximum conversion efficiency is derived.

Photorefractive effect and photochromism in the Fe-doped relaxor ferroelectric crystal Pb(Zn1∕3Nb2∕3)O3-PbTiO3

The photorefractive properties of the iron-doped Pb(Zn1∕3Nb2∕3)O3-PbTiO3 (PZN-PT) relaxor ferroelectric single crystals were investigated by two-beam coupling experiments. The Fe:0.01wt%- and the Fe:0.1wt%-doped 0.91PZN-0.09PT single crystals were grown with the flux solution method. The Extinction spectrum, the electro-opric coefficient, the light-induced absorption change, and the photoconductivity were measured in these samples. The maximum gain coefficient reached to 21cm−1, which is about twice as large as that of undoped PZN-PT. The grating formation rate decreases with the Fe concentration.

Group-velocity-mismatch compensation in cascaded third-harmonic generation with two- dimensional quasi-phase-matching gratings

A novel scheme to achieve broadband cascaded third-harmonic generation by use of two-dimensional quasi-phase-matching gratings is proposed. Intrinsic group-velocity mismatch is compensated by the pulse front tilt in noncollinear interaction geometry. The presented scheme enables broadband third-harmonic generation in a single device of long interaction length, which reduces the operation intensity dramatically.

Photorefractive effect in the relaxor ferroelectric material 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3.

The photorefractive effect in a nominally undoped 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 single crystal is measured. We report what is, to our knowledge, the first observation of the photorefractive effect in Pb-based relaxor ferroelectric crystals. The crystal is grown by the flux solution method. Then it is cut into a 2 mm x 4 mm x 8 mm piece and electrically poled along the [111] direction. The coupling constant of the two-wave mixing is 17 cm(-1), and the normalized time constant under 1-W/cm(2) illumination is 12 s at a wave-length of 476 nm. The effective trap density is calculated as 5 x 10(16) cm(-3) from the Debye screening length under the assumption of Kukhtarevs band-transport model. The dominant carrier is identified to be holes from the direction of two-wave mixing energy transfer.

Detection of small in-plane vibrations using the polarization self-modulation effect in GaP

The adaptive measurement of nanometre-scale vibrations of diffuse surfaces using the polarization self-modulation effect in a photorefractive GaP crystal is described. The sensitivity is investigated as a function of the applied electric field, the intensity of the incident light, and the mean size of the speckles. Numerical estimation of the sensitivity dependence on the mean size of the speckles shows a good agreement with experimental results.

Group-velocity-matched cascaded X (2) -processes in two-dimensional QPM gratings

The simultaneously group velocity (GV) matched second harmonic generation (SHG) and third harmonic generation (THG) of femtosecond pulse in a single 2D quasi-phase-matching (QPM) device have been demonstrated. The conversion efficiencies of 27% for SHG and 7% for THG with the pulse duration of -100 fs was achieved. The demonstration has proved that 2D QPM devices are of significant importance for compact and powerful ultrafast coherent sources. It was believed that the same concept is promising for other multistep chi(2) cascading applications of ultrashort pulses.

Ultrashort pulse cascaded third-harmonic generation in two-dimensional quasi-phase-matching structure

We propose and demonstrate group-velocity mismatch compensation in cascaded third-harmonic generation. Second- and third-harmonic generation efficiency of 25% and 7%, respectively, were experimentally obtained for femtosecond pulses by use of two-dimensionally periodically-poled lithium niobate.

2-D Periodically-Poled LiNbO 3 and Its Application to Broadband 2 nd - and 3 rd -Harmonic Generation

We fabricated a two-dimensional quasi-phase-matching device. Efficient cascaded 2nd- and 3rd-harmonic generation of a 100-fs pulse at 1570 nm is demonstrated. Group velocity mismatch is compensated by pulse-front tilt technique with non-collinear geometry.

Group-velocity matched second- and third-harmonic generations using a two-dimensional quasi-phase-matching device

We demonstrate group-velocity matched secondand third-harmonic generations using a two-dimensional quasi-phase-matching device. Broad spectral responses were experimentally confirmed, and several performances of the scheme are studied with numerical simulations.