This is an 'equipment only' grant under the Defense University Research Instrumentation Program. A report of the results obtained with this equipment is contained in the final report for Grant F49620-95-1-0082, 'Phase-Conjugate Injection Locking of Laser Diode Arrays.' To avoid duplication of paperwork, only a partial summary of that report will be duplicated here. This grant is to produce high-brightness, narrow-frequency light beams from semiconductor laser arrays using optical phase conjugation. The investigators recently demonstrated that their proposed techniques are both practical and efficient, and can be applied to commercially available semiconductor lasers. Their experiments coupled an optical phase conjugator to a broad-area semiconductor laser, causing the laser to emit a 0.5 watt, near-diffraction-limited output beam. Their system is simple and compact, and it also automatically adjusts for any frequency drift or gradual misalignment of the optical components. The investigators extended their techniques from single, broad-area lasers to powerful semiconductor laser arrays.

This goal of this project is to produce a high-brightness, narrow-frequency light beam from a semiconductor laser array. We used a mutually-pumped phase conjugator to couple a single-frequency master laser into a high-power diode laser array. This injected light narrowed the frequency bandwidth of the laser array's output beam. Tuning the master laser (by adjusting its current or its temperature) then smoothly tuned the laser array, while the output beam remained diffraction limited. We compared the performance of the four types of mutually-pumped phase conjugators for injecting light into a laser array. We also invented a new technique for detecting domains hidden in photorefractive crystals. We also measured the phase of the light produced by frequency doubling in a self-phase matched optical fiber. We also measured the anisotropy of the mobility of holes in barium titanate crystals. We found that the drift mobility perpendicular to the crystal's c-axis is 40 times that along the c-axis. We also measured the calibrated small-signal gain spectrum, over a range of eight orders of magnitude, of a single-mode, flared semiconductor amplifier. We found that the detailed-balance theory of semiconductor lasers theory is not consistent with our data. We used a self-pumped phase conjugator to determine a key calibration constant in our experiments.

A complete review of the state of the art of phase conjugate lasers, including laser demonstrations, performances, technology and selection of the most important class of nonlinear media. * Emphasizes the basic aspects of phase conjugation. * Chapter authors have all made major contributions to their subjects.

A huge number of applications require coherent radiation in the visible spectral range. Since diode lasers are very compact and efficient light sources, there exists a great interest to cover these applications with diode laser emission. Despite modern band gap engineering not all wavelengths can be accessed with diode laser radiation. Especially in the visible spectral range between 480 nm and 630 nm no emission from diode lasers is available, yet. Nonlinear frequency conversion of near-infrared radiation is a common way to generate coherent emission in the visible spectral range. However, radiation with extraordinary spatial temporal and spectral quality is required to pump frequency conversion. Broad area (BA) diode lasers are reliable high power light sources in the near-infrared spectral range. They belong to the most efficient coherent light sources with electro-optical efficiencies of more than 70%. Standard BA lasers are not suitable as pump lasers for frequency conversion because of their poor beam quality and spectral properties. For this purpose, tapered lasers and diode lasers with Bragg gratings are utilized. However, these new diode laser structures demand for additional manufacturing and assembling steps that makes their processing challenging and expensive. An alternative to BA diode lasers is the stripe-array architecture. The emitting area of a stripe-array diode laser is comparable to a BA device and the manufacturing of these arrays requires only one additional process step. Such a stripe-array consists of several narrow striped emitters realized with close proximity. Due to the overlap of the fields of neighboring emitters or the presence of leaky waves, a strong coupling between the emitters exists. As a consequence, the emission of such an array is characterized by a so called supermode. However, for the free running stripe-array mode competition between several supermodes occurs because of the lack of wavelength stabilization. This leads to power fluctuations, spectral instabilities and poor beam quality. Thus, it was necessary to study the emission properties of those stripe-arrays to find new concepts to realize an external synchronization of the emitters. The aim was to achieve stable longitudinal and transversal single mode operation with high output powers giving a brightness sufficient for efficient nonlinear frequency conversion. For this purpose a comprehensive analysis of the stripe-array devices was done here. The physical effects that are the origin of the emission characteristics were investigated theoretically and experimentally. In this context numerical models could be verified and extended. A good agreement between simulation and experiment was observed. One way to stabilize a specific supermode of an array is to operate it in an external cavity. Based on mathematical simulations and experimental work, it was possible to design novel external cavities to select a specific supermode and stabilize all emitters of the array at the same wavelength. This resulted in stable emission with 1 W output power, a narrow bandwidth in the range of 2 MHz and a very good beam quality with M²<1.5. This is a new level of brightness and brilliance compared to other BA and stripe-array diode laser systems. The emission from this external cavity diode laser (ECDL) satisfied the requirements for nonlinear frequency conversion. Furthermore, a huge improvement to existing concepts was made. In the next step newly available periodically poled crystals were used for second harmonic generation (SHG) in single pass setups. With the stripe-array ECDL as pump source, more than 140 mW of coherent radiation at 488 nm could be generated with a very high opto-optical conversion efficiency. The generated blue light had very good transversal and longitudinal properties and could be used to generate biphotons by parametric down-conversion. This was feasible because of the improvement made with the infrared stripe-array diode lasers due to the development of new physical concepts.

This volume examines laser beam and control technologies.

With Contributions by Numerous Experts