Andrew J. W. Brown

All-optical switching and routing based on an electromagnetically induced absorption grating

An electromagnetically induced absorption grating is formed in a three-level atomic vapor under the condition of electromagnetically induced transparency in which the strong coupling beam is replaced by a standing wave. The transmission and reflection behaviors of the weak probe beam are greatly modified at certain frequencies near the two-photon resonance. An all-optical two-port signal router-all-optical switch is demonstrated.

Controlled steady-state switching in optical bistability

Optical switching has been achieved between two steady states of optical bistability generated in a system with three-level atoms inside an optical cavity. The optical power switching is controlled by adding short positive (switching up) or negative (switching down) pulses to the input intensity. The coupling laser beam in the three-level atomic system is used to control the threshold value and the width of the hysteresis cycle, which can adjust and optimize the optical switching process.

Competition between two four-wave mixing channels via atomic coherence

Two four-wave-mixing (FWM) processes can coexist in a four-level Y-type atomic system with carefully arranged coupling laser beams. The generated two FWM signal beams fall into two simultaneously opened dual electromagnetically induced transparency (EIT) windows, which can be tuned to overlap or separate by various frequency detunings. The authors report our experimental observation of competing FWM processes, especially mutual suppression of the two FWM signals when the two EIT windows merge in frequency. Controlling FWM processes can have important applications in wavelength conversion for optical communication.

Observation of interference between four-wave mixing and six-wave mixing

We report generation of four-wave mixing enhanced by electromagnetically induced transparency and optical pumping in a ladder-type atomic system. When two pumping laser beams are used to form a conjugate small-angle static grating, both four-wave and six-wave mixing processes are shown to exist at the same time. Interference between these two nonlinear wave-mixing signals is experimentally demonstrated.

High-energy, high-efficiency second-harmonic generation of 1064-nm radiation in KTP

An energy conversion efficiency of 80% for second-harmonic generation of 532-nm radiation from 1064-nm radiation has been achieved with a single KTP crystal and a commerical injection-seeded Q-switched Nd:YAG laser. A second-harmonic output of 720 mJ was generated with 900 mJ of incident 1064-nm radiation at 10 Hz.

Frequency detuning and power dependence of reflection from an electromagnetically induced absorption grating

When the strong-coupling laser beam is replaced by a standing wave under conditions of electromagnetically induced transparency (EIT) in a three-level atomic vapour, an electromagnetically induced absorption grating is formed. The weak probe beam in this EIT system is partially reflected by this absorption grating under certain conditions. The dependences of reflection signals on frequency detuning and coupling laser power are presented.

Efficient, high-energy, narrow-band, blue-light source

In excess of 350 mJ of narrow-band blue (457-nm) light has been generated at 10 Hz through sum-frequency mixing of the output from a cw diode injection-seeded Ti:Al2O3 laser and an injection-seeded Nd:YAG laser. A conversion efficiency of 20% was demonstrated from total 1-μm light to narrow-band blue light at the 200-mJ blue output level. The blue output energy was found to scale closely with the available Ti:Al2O3 energy. A comparison between KD*P and lithium borate as nonlinear mixing crystals has been performed.

Intermixing between four-wave mixing and six-wave mixing in a four-level atomic system

We investigate the interplay between six-wave mixing (SWM) and four-wave mixing (FWM) resulting from atomic coherence and polarization beat in a four-level atomic system. The dressed FWM evolution and competition pathways can be controlled by the coupling field to exhibit two FWM and SWM turning points, FWM+SWM, and FWM+FWM interference regions. Quantum interference between two FWM or one FWM and one SWM channels leads to nonlinear signal enhancement and suppression under different conditions. The fifth-order nonlinear response can be obtained by the phase control of the polarization beat between the FWM and SWM signals.

High-power side-pumped Nd:YVO 4 laser using a grazing incidence cavity

A grazing incidence geometry was used tom ake compact, high power, efficient TEM00, Nd:YVO4 oscillators and amplifiers. A side-pumped Nd:YVO4 laser based on a grazing incidence cavity design, pumped with a 50 W diode bar, achieved 30% optical to optical efficiency at 50 kHz and M2= 1.4 x 1.1 output. The alser was acousto-optically Q-switched and was operated at repetition rates from 20 to 100 kHz, as well as operating continuous-wave (CW). Multiple cavity designs were developed to optimize performance for short (<10ns) and longer (>30ns) pulse durations. 15 W of TEM00 output was generated at 50 kHz and used to pump a periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO), generating 5 W of eye safe output at 1.5 μm. This oscillator/OPO system was packaged on a 4 x 6 inch optical platform. Using an oscillator/amplifier/amplifier configuration, 30 W of 1.064 μm output power was generated at 50kHz and subsequently converted in an OPO to 10.25 W of eye safe output in a PPLN OPO. This work demonstrates that the side-pumped grazing incidence geometry scales to high power and maintains M2 and efficiency while fitting in a compact package.

Stimulated Brillouin scattering in multimode fibers

The propagation of high power narrowband laser pulses in multimode fibers and the limitations due to SBS are presented. An injection seeded pulsed Nd:YAG laser operating at 10 Hz was used to pump undoped step index fibers to determine the SBS threshold under various conditions. Measurements on 50μm core diameter fibers with various fiber lengths and pulse durations at 1064 nm were performed and simulated with a computer code. The code considers the time dependent coupling between the pump wave, the Stokes wave, and the acoustic wave. The experimental results are in good agreement with the numerical predictions. Our results quantify the limitations of high power narrowband pulse transmission in multimode fibers.