Stuart MacCormack

Injection locking a laser-diode array with a phase-conjugate beam.

We use a mutually pumped phase conjugator to guide the output beam of a single-mode laser diode into the active region of a high-power laser-diode array. This injected beam locks the frequency of the array, causing it to emit a single, 1.45 times diffraction-limited, continuous-wave output beam containing 85% of the array’s total output power. Phase-conjugate injection dramatically improves the coupling into the laser array, so that less than a milliwatt of injected power is sufficient to lock all the array’s 450-mW output to the frequency of the master laser.

Effect of beam coherence on mutually pumped phase conjugators

The performance of four different mutually pumped phase conjugators in barium titanate depends on the mutual coherence of the two input beams. In three of the conjugators the use of fully mutually coherent input beams enhances the overall phase-conjugate reflectivity. We find that backscattering and transmission gratings in the photorefractive crystal both contribute to the phase-conjugate signal and that their relative strength depends on the relative coherence of the two input beams. We numerically solve coupled-wave equations that include all gratings and find reasonable agreement between our theory and our experimental data.

High-brightness output from a laser-diode array coupled to a phase-conjugating mirror

We obtain single-lobed, near-diffraction-limited output from a 20-element laser-diode array coupled to an apertured photorefractive phase conjugator. At low driving currents the output beam is diffraction limited and contains 75% of the total output power emanating from the array. At high driving current a 1.5× diffraction-limited lobe contains 490 mW of power, or 54% of the output power. By studying the near-field emission pattern and the frequency spectrum of the laser, we confirm that the apertured conjugator selects a narrow range of output array transverse modes.

All-optical three-dimensional mapping of 180° domains hidden in a BaTiO 3 crystal

We present three-dimensional, high-contrast maps of 180° domains hidden inside photorefractive crystals of BaTiO3. Some domains are columns that run the entire length of the crystal, whereas others are short needles that begin predominantly on the −c surface but disappear inside the crystal bulk.

110 W fiber laser

We demonstrate a Yb-doped double-clad fiber laser with record average power output of >110 W cw in a single spatial mode beam. The conversion efficiency was /spl sim/58% with respect to the incident pump power.

Powerful, diffraction-limited semiconductor laser using photorefractive beam coupling

We use semiconductor laser amplifiers and a photorefractive crystal to generate a high-power, diffraction-limited laser beam at 860 nm. Using a single flared amplifier, we obtain 1.09 W in a diffraction-limited beam from 2.2 W of pump power. Using an array of flared amplifiers, we also demonstrate efficient beam coupling, showing that this technique is easily extended to semiconductor amplifier arrays.

High-speed, high-power double-clad fiber amplifiers

Double-clad optical fibers are a robust, convenient medium for efficient optical amplification. Their compatibility with high-power semiconductor laser pump sources allows them to operate at saturated power levels of several watts, significantly higher than the level achievable with conventional diode-pumped fiber amplifiers. When coupled with a high-speed master oscillator, such an amplifier becomes an efficient high-speed, high-power optical transmitter. Such a source is of considerable interest for a high-speed space link. The transmitter consisted of a high-speed master laser diode, a high-gain fiber preamplifier, and a high-efficiency fiber power amplifier. The master oscillator was a Fabry-Perot laser diode centered at /spl lambda/=1072 nm, mounted in a high-speed, fiber-coupled package. The laser operated kink free to >50 mW and exhibited a 3-dB roll-off frequency of 11.1 GHz. Both the pre-amp and power amp were based on Yb-doped double-clad fibers pumped with /spl lambda/=915 nm fiber-coupled laser diodes. A polarization-independent optical isolator prevented feedback from the amplifier destabilizing the master oscillator. A free-space WDM module used to combine the signal and pump light into the core and cladding, respectively, of the pre-amp fiber, is shown.

REVEALING 180 DOMAINS IN FERROELECTRIC CRYSTALS BY PHOTOREFRACTIVE BEAM COUPLING

We describe a simple, optical technique for mapping 180° domains hidden inside photorefractive crystals. We intersect two coherent light beams in the crystal. Photorefractive coupling between the two beams causes one beam to emerge with a map of all the crystals 180° domains imprinted upon it. We tested many BaTiO(3) crystals and found that they all contained 180° domains, with the relative volume of these domains varying from 25% to 0.1%.

Photorefractive properties of rhodium doped barium titanate

Summary form only given. We have measured the effective trap density, the number of active trap levels, the sign of the dominant charge carrier, and the photorefractive two-beam coupling gain of four rhodium-doped crystals of BaTiO/sub 3/, all grown at Hughes Research Laboratories.<<ETX>>

Efficient quasi-phase-matched frequency doubling of a high power, unpolarized fiber laser source

Summary form only given. The combination of sum frequency generation (SFG) and SHG processes has generated 590 mW of green light from a planar periodically poled lithium niobate (PPLN) waveguide, which, to the best of our knowledge, is the highest power ever reported from such a device. In this experiment, combining the SFG and SHG processes within the planar waveguide produced 35% more green power than would be obtained by frequency doubling the two infrared polarizations separately.