IEEE Journal of Quantum Electronics

The evaluation of pump capability and scaling the output power of Nd:YVO/sub 4/ (vanadate) lasers are presented in this paper. Taking into account thermal fracture limitation and fundamental mode operation, systematic investigations of vanadate crystals have been conducted in an effort to scale the output power of diode-pumped lasers to higher levels. Based on the limitation of pump power, the input versus output power and beam propagation factor of vanadate lasers are optimized with knowledge of the thermal lensing effect and maximum pump power. The theoretical analyzes provide a good prediction for the output power of diode-pumped Nd:YVO/sub 4/ lasers, which is in agreement with the experiment. A practical example of a single-end-pumped vanadate laser is demonstrated with continuous-wave output powers of 9.8 W in the TEM/sub oo/ mode and 12.4 W in multimode.

The accurate computation of the propagation constants and field distributions of different modes in nonlinear optical dielectric waveguides is addressed in this paper. Using the vector finite-element formulation of the beam propagation method, combined with the imaginary distance propagation technique, both linear and nonlinear modes can be accurately calculated. The proposed technique is applied to obtain the fundamental TE nonlinear mode of a strip-loaded waveguide, and the excellent agreement seen with published results shows its high numerical precision.

A new model is proposed for the active modulation component of a mode-locked laser cavity. By using Jacobi elliptic functions to capture the periodic forcing to the cavity, we are able to construct exact solutions representing a mode-locked pulse train. Two families of pulse-train solutions are generated: one in which neighboring pulses are in-phase and a second in which neighboring pulses are out-of-phase. We show that only out-of-phase solutions allow for stable mode-locked pulse trains. Further, pulse-to-pulse interactions can generate instabilities that destroy the pulse train altogether or lead to Q-switching.

We investigate nonlinear waveguiding effects, due to second-order nonlinearity, in quasi-phase-matching (QPM) structures in periodically poled lithium niobate (PPLN) with engineered patterns. We specifically study the existence and the propagation of pure nonlinear guided modes in QPM gratings with different domain lengths in different transverse regions of the medium, without any waveguiding effect due to linear refractive index changes. On one hand, the obtained results enlighten the possibility of soliton operation at lower intensity thresholds than in standard not-tailored PPLN structures. On the other hand, in such nonlinear engineered structures, we reveal the presence of intensity-dependent attractive and repulsive potential wells that can be exploited for soliton control (resonant trapping and emission) in quadratic nonlinear media.

We succeeded in observing one of the absorption lines of acetylene [P(16)] using an erbium-doped fiber-ring laser, which is the first such observation using a fiber-ring laser. The observed linewidth of the P(16) linear absorption was approximately 450 MHz. Mode competition and mode hopping were suppressed by using an ultra narrow-band fiber Bragg grating and a Fabry-Perot filter in the ring laser, respectively. Wavelength fine-tuning was carried out by changing the cavity length of the fiber-ring laser; the fine-tuning range was about 850 MHz (0.01 nm). Furthermore, wavelength tuning was achieved by controlling the temperature of the fiber Bragg grating, and the coarse timing range was about 0.2 mn.

We describe an ongoing study of nanoheteroepitaxy (NHE), the use of nanoscale growth-initiation areas for the integration of highly mismatched semiconductor materials. The concept and theory of NHE is briefly described and is followed by a discussion of the design and fabrication by interferometric lithography of practical sample structures that satisfy the requirements of NHE. Results of NHE growth of GaAs-on-Si and GaN-on-Si are described, following the NHE process from nucleation through to coalescence. Micro-Raman measurements indicate that the strain in partially coalesced NHE GaN-on-Si films is <0.1 GPa.

Photomodulated reflectance (PR) and conventional reflectance studies have been performed on an InGaP/AlGaInP/Al/sub x1/Ga/sub y1/As/Al/sub x2/Ga/sub y2/As resonant-cavity light emitting diode structure in the red spectral region. The PR spectra show prominent signals from the Fabry-Perot cavity mode and the quantum-well (QW) ground state excitonic transition. This high-precision technique, and its variations as functions of incidence angle and temperature, as reported in this article, allow one to investigate light emission from the QW confined in a microcavity with relation to the Fabry-Perot mode, and is the only known nonconductive, nondestructive method of doing so.

We present a comprehensive study on multigigahertz repetition rate Nd:YVO/sub 4/ lasers, passively mode-locked with semiconductor saturable absorber mirrors. A brief review of Q-switching instabilities with special emphasis on high repetition rate is given. We then present basic design guidelines, and experimentally show that one can push the pulse repetition rate of a Nd: YVO/sub 4/ laser up to 157 GHz, reaching the fundamental limit to the repetition rate which is given by the pulse duration and thus by the amplification bandwidth. We also demonstrate an air-cooled diode-pumped 10-GHz Nd: YVO/sub 4/ laser with 2.1-W average output power and 13% electrical-to-optical efficiency, showing the potential of solid-state lasers generating multiwatt, multigigahertz pulse trains with high efficiency.

A multi-reentrant nonplanar ring laser cavity configuration is presented. Two identical spherical mirrors were used to construct the laser cavity. The exact reentrant condition of the ring cavity is derived and the stability of the laser cavity is analyzed. Although slight astigmatism can arise from the intracavity elements, the cavity itself is astigmatism-free. Linear output polarization is readily achieved. A 3-atm.% Nd doped YAG with 1-mm thickness was used as the gain medium to reduce beam distortion, and the gain medium also served as a Faraday rotator to control the laser beam propagation direction. The laser cavity length is short, whereas the laser beam round-trip length can be long. A factor of 13-times enlargement in round-trip length is demonstrated.

For the first time, a wide tunability waveguide CO/sub 2/ laser was used to pump the CHD/sub 2/OH molecule for the generation of new FIR laser lines with a large offset. Optoacoustic signals associated with the infrared absorbing transitions of the CD/sub 2/ wagging vibrational mode served as a guide for finding new laser lines. All lines were characterized in wavelength, relative polarization, intensity, optimum pressure of operation, and precise offset measurements.