H. Rhee

New nonlinear-laser effects in YbVO4 crystal: Sesqui-octave stokes and anti-Stokes comb generation and the cascaded self-frequency “tripling” of χ(3)-Stokes components under a one-micron picosecond pumping

We report the experimental investigations of nonlinear-laser effects in vanadate YbVO4 under a onemicron picosecond Nd3+:Y3Al5O12 laser pumping. In this tetragonal host-crystal for Ln3+ lasants, for the first time, we excited more than one-and-a-half octave (≈11661 cm−1) Raman-induced Stokes and anti-Stokes generation combs and observed a multistep cascaded parametric χ(3) lasing in the deep-blue spectral region. All generation lines were identified and attributed to the SRS-promoting vibration mode of the crystal (ωSRS ≈ 897 cm−1). We classified the ytterbium vanadate as a promising material for Raman frequency converters, wideband χ(3)-nonlinear comb generators, and as a gain medium for solid-state lasers.

Multi-octave frequency comb generation by χ(3)-nonlinear optical processes in CVD diamond at low temperatures

We study stimulated Raman scattering (SRS) and Raman four-wave mixing (RFWM) processes in chemical vapour deposition (CVD) diamond crystals. The strong interaction of picosecond laser pulses at 1.064 and 0.532 µm wavelength with the dominant Raman-active F2g mode results in a more than two-octave-spanning frequency comb, ranging from the UV to the NIR spectral region. In addition to spectroscopic analysis of the χ(3)-nonlinear emission at room temperature, comparative measurements have been carried out at cryogenic temperature of 10 K. The Raman shift and the Raman gain are found to change only weakly. Moreover, the potential of SRS frequency comb generation in CVD diamond for ultra-short pulse synthesis is discussed.

Frequency conversion concepts for the efficient generation of high power 935 - 942 nm laser radiation

The three-dimensional measurement of the global water vapor distribution in the atmosphere considerably improves the reliability of the weather forecast and climate modeling. A spaceborne Differential Absorption Lidar (DIAL) is able to per-form this task by use of suitable absorption lines of the broad absorption spectrum of water vapor. Because no interference with the absorption of other molecules exists, the range of 935/936 nm, 942/943 nm are the most preferred wavelength ranges for a water vapor DIAL. The challenge is to develop a dedicated efficient high power laser source emitting at these wavelengths. The comparison between frequency converters based on stimulated Raman scattering (SRS) and Ti:Sapphire and the directly generated Mixed Garnet laser shows the favorable properties of each concept and helps to evaluate the most suitable concept. Development of Raman frequency converters for high pulse energies concentrates on linear resonator de-signs and seeding using the Raman material as a direct amplifier based on Raman four-wave-mixing. In addition a seeded and frequency stabilized pulsed Ti:Sapphire laser system with output pulses up to 22 mJ injection-seeded at the water vapor absorption line at 935.684 nm with a spectral purity up to 99.9 % has been developed. Direct generation of the wavelengths 935/936 nm and 942/943 nm required for water vapor detection is possible with diode-pumped, Nd-doped YGG- and GSAG-crystals. First experiments resulted in pulse energies of 18 mJ in Q-switched and 86 mJ in free-running operation at 942 nm wavelength.

Stimulated Raman scattering spectroscopy of Y0.4Gd0.6VO4 crystals with partly disordered zircon-type structure—observation of new χ(3)-nonlinear optical interactions

This letter presents the results of stimulated Raman scattering (SRS) spectroscopy of tetragonal Y0.4Gd0.6VO4 vanadate crystals having a partly disordered zircon-type structure. Picosecond laser pumping revealed previously unexplored χ(3)-nonlinear interactions comprising the generation of an almost two-octave spanning Stokes and anti-Stokes frequency comb, self-third harmonic generation as well as cross-cascaded processes involving four different Raman-active modes. The recorded spectral lines have been assigned to the participating molecular vibrational modes of the (VO4)3− structural units of the studied crystal. In addition, this work provides a brief review of all known SRS-active tetragonal and monoclinic vanadates of the form REVO4 including their χ(3)-nonlinear properties and steady-state Raman gain coefficients for first Stokes generation.

Operation of a Raman laser in bulk silicon

A Raman laser based on a bulk silicon single crystal with 1.127 μm emission wavelength is demonstrated. The Si crystal with 30 mm length was placed into an external cavity and pumped by a Q-switched Nd:YAG master oscillator power amplifier system. Strong defocusing of the pump and Raman laser beam by free carriers was compensated by an intracavity lens. Raman laser operation with a pulse duration of 2.5 ns was identified by a Raman laser threshold significantly lower than the single-pass stimulated Raman-scattering threshold. Linear absorption losses of the 1.06415 μm pump radiation are strongly reduced by cooling the Si crystal to a temperature of 10 K.

Efficient laser systems for 935 and 942 nm for water vapor lidar

Water vapour absorption wavelengths have been directly generated by diode pumped Nd:YGG crystals emitting at 935 nm and with Nd:GSAG crystals emitting at 942 nm in cw and pulsed operation. In addition the 1064 nm fundamental wavelength from Nd:YAG pump lasers with pulse lengths of 10 or 20 ns was shifted using Stimulated Raman Scattering (SRS) or Ti:Sapphire (TiSa) lasers. The potential of Nd:GSAG, Nd:YGG, SRS and TiSa laser systems is compared for future incorporation into a satellite based Lidar system. High output energies are possible by recent advances of fiber coupled diode sources allowing pulsed longitudinal pumping of Q-switched solid state lasers.

25 Gb/s Silicon Photonics Interconnect Using a Transmitter Based on a Node-Matched-Diode Modulator

In this article a nonreturn-to-zero data transmission of 25 Gb/s between silicon photonic transmitter and receiver units is demonstrated, where the transmitter is based on a silicon optical Fabry-Pérot modulator with a node-matched-diode geometry. This modulator type has a footprint of less than 100 μm2. On the receiver side, an integrated Ge-photo detector has been used. Mask tests according to the 100G ER4 standard have been performed and yielded error free data transmission.

Monoclinic LaGaGe2O7:Nd3+—a novel SRS- and SE-active crystal with high-order Stokes and anti-Stokes picosecond χ(3)-nonlinear lasing

Steady-state ?(3)-nonlinear generation in the host crystal LaGaGe2O7 for Nd3+(Ln3+)-lasants has been discovered. All the registered Stokes and anti-Stokes lasing sidebands are identified and attributed to its SRS-promoting phonon mode at ?SRS???882?cm?1. We have classified the studied germanate as a promising crystal for self-Raman laser converters.

High-Speed Fabry–Pérot Optical Modulator in Silicon With 3-μm Diode

A silicon optical modulator using a novel node-matched-diode geometry inside a Fabry-Pérot nanowaveguide resonator is presented. The diode length is only 3 μm. An analysis of the dynamic spectral transmission behavior is given. Non-return-to-zero data transmission of 10 Gb/s is demonstrated.

Monoclinic m-LaVO4—a novel high Raman gain SRS-active crystal

Monoclinic m-LaVO4, having a monazite-type structure and being known as a host crystal for Nd3+-lasants, is an attractive χ(3)-nonlinear optical material for Raman laser converters. This paper presents the stimulated Raman scattering (SRS) spectroscopy of m-LaVO4 in the visible and near-IR spectral range using picosecond laser excitation. High-order SRS and Raman-induced four-wave parametric mixing processes result in an almost two-octave-wide Stokes and anti-Stokes frequency comb. All the measured spectral lines were assigned to the participating molecular vibration modes of the studied vanadate. Finally, an estimation of the steady-state Raman gain coefficient for first Stokes generation in near-IR was performed.