Gustav Strömqvist

Fabrication of submicrometer quasi-phase-matched devices in KTP and RKTP [Invited]

We review the techniques used for fabrication of bulk submicrometer ferroelectric domain gratings in KTiOPO4 (KTP) and demonstrate that bulk Rb-doped KTiOPO4 (RKTP) is an excellent candidate for im ...

Control of forward stimulated polariton scattering in periodically-poled KTP crystals

We report suppression of forward stimulated polariton scattering (SPS) in χ((2)) structured media. Periodic poling in KTiOPO(4) (KTP) leads to the destructive interference of phonon-polariton waves, which is responsible for the dependence of the SPS threshold on the poling period. This was confirmed by comparing the SPS thresholds in periodically-poled KTP (PPKTP) crystals with different poling periods. Further confirming the physical picture, we studied the changes in the Stokes power distribution as a function of the rotation angle of the PPKTP crystal.

Temporal coherence in mirrorless optical parametric oscillators

One of the unique features of mirrorless optical parametric oscillators based on counterpropagating three-wave interactions is the narrow spectral width of the wave generated in the backward direct ...

Tandem PPKTP and ZGP OPO for mid-infrared generation

Efficient laser sources in the 3 - 5 μm wavelength range are needed for directed infrared countermeasures, but also have applications in remote-sensing, medicine and spectroscopy. We present new results on our tandem optical parametric oscillator (OPO) scheme for converting the radiation from a 1.06 μm Nd3+-laser to the mid-infrared. Multi Watt level output power in the 3-5 μm range at 20 kHz pulse repetition frequency is reported. Our setup uses a type I quasi phase-matched PPKTP crystal in a near degenerate OPO to generate 2.13 μm radiation. A volume Bragg grating resonant close to, but not exactly at the degenerate wavelength, is used as a cavity mirror to reduce the bandwidth and ensure singly resonant operation. Both signal and idler from the PPKTP OPO are used to pump a ZGP OPO generating high power radiation in the 3-5 μm region. Using this scheme for each pump photon it is possible to generate four photons for each pump photon, all in the interesting wavelength range, thus enabling high efficiency conversion.

Self-established noncollinear oscillation and angular tuning in a quasi-phase-matched mirrorless optical parametric oscillator

We experimentally demonstrate self-established noncollinear interactions in a quasi-phase-matched mirrorless optical parametric oscillator using a periodically-poled KTiOPO4 crystal with submicrometer periodicity. It is shown that the oscillation is established in a very specific geometric configuration where the two possible solutions of the energy and momentum conservation conditions become spatially degenerate and contribute coherently to the gain. In this configuration, the signal and the idler remain mutually counter-propagating. The tuning capabilities of a noncollinear mirrorless optical parametric oscillator are investigated.

Counter-propagating parametric interaction with phonon-polaritons in periodically poled KTiOPO 4

Strongly enhanced backward stimulated polariton scattering (BSPS) is demonstrated in periodically-poled KTiOPO4 (KTP) crystals with a high power-conversion efficiency up to 70%. We study the physical mechanism of such counter-propagating parametric interaction with phonon-polaritons in χ(2) modulated structures. BSPS is a three-wave mixing that is distinguished from backward stimulated Raman scattering (BSRS), while a strong absorption at large polariton wave-vectors can still make BSPS display certain characteristics of BSRS such as self-compression of the Stokes pulse. We also compare BSPS with counter-propagating parametric oscillation in the near- and mid-infrared range, providing an estimation of the fabrication error margin to expect the outcome of their competition in the same device.

Investigation by coherent X-ray section topography of ferroelectric domain behaviour as a function of temperature in periodically poled Rb:KTP

The behaviour of ferroelectric domains at high temperatures near the Curie temperature in a periodically poled rubidium-doped potassium titanyl phosphate crystal (Rb:KTP) has been studied by Bragg-Fresnel X-ray diffraction imaging in situ using a compact coherence-preserving furnace. The development and partial disappearance of the inverted domain structure as the temperature increases has been successfully modelled, and is explained by invoking a built-in electric field produced under heating in a low vacuum by out-diffusion of atoms from the sample.

Nonlinear Refractive Indices in Disordered NaT(XO 4 ) 2 T = Y, La, Gd, Lu and Bi, X = Mo, W Laser Crystals

Nonlinear index has been measured using z-scan technique in tetragonal disordered double tungstate and molybdate laser crystals. The n2is comparable or larger than in monoclinic double tungstates, with substantial enhancement found in NaBi(WO4)2.

Control of forward stimulated polariton scattering in periodically poled nonlinear crystals

Periodic poling in KTP leads to periodic phase reversal of the polaritons generated in Cherenkov phase-matched direction. This is responsible for the dependence of stimulated Raman scattering threshold on crystal rotation angle and poling period.

Nonlinear refractive indices in undoped and Yb-doped KT(WO 4 ) 2 T=Y, Yb, Gd, Lu crystals

Nonlinear index was investigated in undoped and Yb-doped monoclinic double-tungstates for E∥N<inf>m</inf> and E∥N<inf>p</inf> polarized 819 nm light. Anisotropic n<inf>2</inf> with maximum for E∥N<inf>m</inf> in all investigated compounds is proportional to the rare earth ion polarizability.