We demonstrate a frequency-converted green laser source simultaneously emitting three spectral lines with nearly equal
intensity and ~ 0.5 nm separation, enabling a factor of √3 reduction of speckle contrast in pico-projector applications.
The source consists of an external cavity 1060 nm diode laser pump with dual-wavelength reflection provided by a
volume Bragg grating and a quasi-periodically poled MgO-doped lithium niobate waveguide engineered to phase-match
multiple-wavelength frequency conversion. 62 mW output power and 33% conversion efficiency are demonstrated.
We describe reverse-proton exchanged (RPE) waveguides in MgO-doped lithium niobate capable of stable secondharmonic
generation (SHG) of over 100 mW of CW green light with conversion efficiency exceeding 200%/Wcm2.
Substantially higher green power would require careful thermal management to limit the phase mismatch due to heating
produced by optical absorption. RPE waveguides show ability to support high-power generation of green light superior
to anneal-proton exchanged (APE) waveguides containing a higher-index layer. We also demonstrate devices with multipeak
spectral response for speckle-reduced green laser by using phase-modulated, quasi-periodic ferroelectric domain
structure.
The ability to achieve high quality periodic poling in lithium niobate (LN) has allowed quasi-phase-matching to be used for second-order nonlinear optics, leading to experimental demonstration of efficient optical frequency generation throughout its wide transparency range (0.35-4.5 microns). Applications of congruent lithium niobate involving visible or ultraviolet wavelengths are limited to low power or high temperature operation due to the effects of photorefractive damage (PRD) and green-induced infrared absorption (GRIIRA). The standard methods of suppressing PRD include doping with 5 mol-% MgO or ZnO and varying crystal stoichiometry. More recent methods employ a combination of lower doping level and near-stoichiometric composition. We use vapor transport equilibration (VTE) and significantly lower MgO doping (<0.5% in the melt) to obtain near-stoichiometric PRD-resistant crystals with improved parameters for periodic poling compared to the commercially available 5% MgO-doped congruent crystals. An efficient process for periodic poling at room temperature using baked photoresist as a patterned dielectric on one crystal surface with LiCl-solution electrodes was developed for periods as short as 8.3 microns for 0.5% and 7 microns for 0.3% MgO-doped VTE:LN. The quality of periodic poling improves as the MgO concentration is lowered. Stable second harmonic generation of 1.3-W continuous-wave 532-nm radiation was observed near room temperature (43 degrees Celsius, as determined by the phase matching condition) with no sign of degradation in a 1.5-cm long crystal of 0.3-% MgO-doped VTE:LN periodically poled with a period of 7.06 microns.
We use a combination of vapor transport equilibration and moderate MgO doping (≤1%) to explore near-stoichiometric damage resistant lithium niobate crystals with improved properties for periodic poling and annealed-proton-exchange waveguide fabrication compared to the commercially available 5-mol% MgO-doped crystals. High damage resistance, measured by the saturated space-charge field generated in the crystal by 514 nm radiation, was obtained for all MgO doping concentrations (0.3, 0.5 and 1%) with appropriate equilibration. Green-induced infrared absorption was also measured in the 0.3-% doped crystal and was below the detection limit. Dispersion in the region 460-1550 nm was measured. Periodic poling was performed using LiCl solution electrodes. Poling quality improves with lowering MgO concentration. Waveguides for frequency doubling of 1550 nm were fabricated in the 1% doped crystal with losses as low as 0.4 dB/cm and normalized efficiency of ~10%/Wcm2.
As the demand for optical fiber communications bandwidth grows, the implementation of signal processing functions using all-optical techniques becomes increasingly attractive. In recent years, a number of methods have been used to perform functions such as wavelength conversion for WDM systems, gated mixing for TDM multiplexing and demultiplexing, spectral inversion for dispersion compensation, and all-optical switching. Three-wave mixing in c(2) media is an attractive approach, presenting a combination of low pump power, wide bandwidth, and negligible degradation of signal to noise ratio. In this paper, we describe optical frequency mixers implemented using annealed proton exchanged waveguides in periodically poled lithium niobate. These devices have been used in a variety of system experiments. We present several WDM demonstrations, including wavelength conversion, dispersion compensation by mid-span spectral inversion, and compensation of Kerr nonlinearities. We also discuss TDM demonstrations such as efficient all-optical gating and multiplexing/demultiplexing of high bit-rate data streams.
As the demand for optical fiber communications bandwidth grows, the implementation of signal processing functions using all-optical techniques becomes increasingly attractive. In recent years, a number of methods have been used to perform functions such as wavelength conversion for WDM systems, gated mixing for TDM multiplexing and demultiplexing, spectral inversion for dispersion compensation, and all-optical switching. Three-wave mixing in (chi) (2) media is an attractive approach, presenting a combination of low pump power, wide bandwidth, and negligible degradation of signal to noise ratio. In this paper, we describe optical frequency mixers implemented using annealed proton exchanged waveguides in periodically poled lithium niobate. These devices have been used in a variety of system experiments. We present several WDM demonstrations, including wavelength conversion, dispersion compensation by mid-span spectral inversion, and compensation of Kerr nonlinearities. We also discuss TDM demonstrations such as efficient all-optical gating and multiplexing/demultiplexing of high bit-rate data streams.
Studies of the radiative lifetimes of some of the Beutler (formula available in paper) states of the mercury atom have allowed us to propose an inversion population mechanism for some of the laser actions observed previously. Most of the laser transitions in HgI are in the IR spectral region and few of them are connected with the Beutler states. We focused on the (formula available in paper) ((lambda) equals 5.88(mu) ) transition. A qualitative analysis of this laser transition is proposed.
In this work we present a theoretical estimation for VUV superluminescent laser gain employing electron-impact excitation and Super-Koster-Cronig decay in Zn vapors. The stimulated emission is produced on the 3d84s21G4 - 3d94p 3D3 130.6 nm two-electron transition of ZnIII. We use the existing information on atomic constants available in the literature to estimate the current densities that will be necessary to observe a significant gain, comparable to that observed in an experiment using x-ray excitation, produced in laser induced plasma. Our estimations show that such values of the gain are obtainable by pulsed electron excitation with time longitude greater than 1 microsecond(s) and high but possible current densities of the order of 10 kA/cm2.
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