Abstract We study the effects of pump beam focusing and polarization inhomogeneity on second-harmonic generation (SHG) in a 3 cm long type-II ppKTP crystal. Focusing leads to an asymmetry in the SHG output power around the phase-matching temperature (PMT), along with a shift of the PMT to a lower temperature. Theoretical predictions are experimentally verified for different focusing parameters at various pump wavelengths, showing maximum SHG of 0.24% W −1 (close to optimal focusing). Further, an inhomogeneous polarization across the pump beam cross-section is theoretically predicted to break up the SHG transverse (intensity) profile into several lobes, resulting in an overall decrease in the total output power. We experimentally show that a radially/azimuthally polarized pump beam (generated via a Q-plate) results in a four-lobed SHG similar to the Hermite–Gaussian HG 11 mode with an optimal focusing parameter that is four times higher than that for the homogeneously polarized pump.
Lithium niobate on insulator platform, with excellent light confinement and second order nonlinearity, has recently attracted great interest for applications towards next-generation wavelength conversion systems that are highly efficient and can be densely fabricated. Here we propose and experimentally demonstrated efficient quasi-phase matched second harmonic generation in periodically-grooved lithium niobate waveguides with sub-micron dimensions. We show that, an additional momentum kick induced by periodically modulating the waveguide width could be used to compensate for the phase mismatch between the two fundamental modes at pump and second harmonic wavelengths. We measure normalized conversion efficiencies as high as 7.0% W-1cm-2 from the fabricated devices. This system is promising for future on-chip quantum wavelength conversion.
We investigate the time dynamics of light-induced desorption of Rb atoms in hollow-core photonic-band-gap fibers and demonstrate all-optical generation of precisely controlled Rb-vapor densities. We also compare the performance of the desorption process in an unmodified fiber with one with an organosilane-coated core, and based on the vapor depletion and recovery behavior, we propose a mechanism to describe the desorption processes. We further demonstrate that high densities of Rb vapor can be generated after the desorption beam is switched off and use it to realize $\ensuremath{\Lambda}$-scheme electromagnetically induced transparency at control powers as low as 80 nW.
Using light-induced atomic desorption, we generate an optically-dense Rb vapor on- demand inside a hollow-core photonic bandgap fiber for ultralow power nonlinear optical interactions. We demonstrate electromagnetically-induced-transparency, four-wave-mixing and efficient all-optical modulation in this system.
We propose simplified reduced 5-level and 7-level rate equation models to calculate saturated absorption spectra of the Rb D 2 line, and experimentally verify for transitions from upper and lower hyperfine ground state of 87 Rb, respectively.
A new Grounded Lamination Gate (GLG) structure is proposed in which grounded metal film is deposited in the spacer region on both sides of the gate to prevent the fringing field lines emanating from the bottom of the gate electrode from entering the source/drain regions. The variation of threshold voltage with gate dielectric permittivity is obtained for both the GLG and the conventional SOI MOSFETs using MEDICI. We demonstrate that the application of grounded lamination gate (GLG) structure is very effective in controlling the threshold voltage roll-off even for high gate dielectric permittivities.
We characterize the diffusion and redistribution processes that Rb atoms undergo on the inner silica surface of hollow-core photonic bandgap fibers by investigating the dynamics of fiber-transmission and light-induced atomic desorption.
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