We demonstrated mutual injection locking and coherent beam combining of three individual Nd:YVO<sub>4</sub> laser modules. A beam splitter couples three lasers as well as combines their outputs. In the free running state, the divergence of combined beams is large. Under mutual injection locking, the divergence of the combined beams becomes substantially smaller than that in the free-running state and is as small as that of the individual laser beam. Mutual injection locking was also realized without active stabilization with large individual laser cavity length difference and low individual laser Q-factor.
Lasers have come a long way since the first demonstration by Maiman of a ruby crystal laser in 1960. Lasers are used as scientific tools as well as for a wide variety of applications for both commercial industry and the military. Today lasers come in all types, shapes and sizes depending on their application. The solid-state laser has some distinct advantages in that it can be rugged, compact, and self contained, making it reliable over long periods of time. With the advent of diode laser pumping a ten times increase in overall laser efficiency has been realized. This significant event, and others, is changing the way solid-state lasers are applied and allows new possibilities. One of those new areas of exploration is the high energy laser. Solid-state lasers for welding are already developed and yield energies in the 0.5 to 6 kilojoule range. These lasers are at the forefront of what is possible in terms of high energy solid-state lasers. It is possible to achieve energies of greater than 100 kJ. These sorts of energies would allow applications, in addition to welding, such as directed energy weapons, extremely remote sensing, power transfer, propulsion, biological and chemical agent neutralization and unexploded and mine neutralization. This article will review these new advances in solid-state lasers and the different paths toward achieving a high energy laser. The advantages and challenges of each approach will be highlighted.
The Army has initiated a flexible display research program. This program is part of the Army's strategy to create technologies that will enable revolutionary designs and transformational weapons systems for the Objective Force. The ARL flexible display program is more general than just for the dismounted soldier-it will also have implications for air and vehicular crews, and for the other services, even though it is not a DoD tri-service program per se. “Flexible” is defined in the program as displays that operate under conditions from conformal applications, limited flexing, to rollable displays for compact storage. The Army program will include display manufacturing concepts that enable roll-to-roll processes reduce cost, to tap a strong U.S. domestic industrial strength, and, eventually, to enable fabrication of very large sizes. There is commercial interest in flexible displays for applications ranging from wearable electronics for road-warriors and gamers to large screen 71-in. 1920x1200 color pixel consumer high definition television sets for walls. Industry willingness to cost share will be a key criterion in identifying investment opportunities that are necessary and timely from among all that may be envisioned. Some anticipated military applications and a roadmap are presented that identify the technology barriers at the materials, device and manufacturing levels to the creation of flexible display technology.
A novel methodology has been developed for the investigation of bacterial spores. Specifically, this method has been used to probe the spore coat composition of several Bacillus species. This technique may be useful in many applications; most notably, development of novel detection schemes toward potentially harmful biological agents. This method would also be useful as an ancillary environmental monitoring system where sterility is of importance (i.e., food preparation areas as well as invasive and minimally invasive medical applications). This unique detection scheme is based on the near-infrared (NIR) Surface-Enhanced-Raman-Scattering (SERS) from single, optically trapped, bacterial spores. The SERS spectra of several bacterial spores in aqueous media have been measured using SERS substrates based on 60-nm diameter gold colloids bound to 3-Aminopropyltriethoxysilane derivatized glass. The light from a 785-nm laser diode was used to capture/manipulate as well as simultaneously excite the SERS of an individual bacterial spore. The collected SERS spectra were examined for uniqueness and the applicability of this technique for the species identification of bacterial spores.
The rapid advances in full-color displays based on organic light emitting devices (OLEDS) and advances in nonemissive technologies have opened new military and commercial applications. For emissive displays, organic based devices are uniquely capable of being deposited at room temperature, which offers the possibility for fabrication on flexible substrates. Most passive technologies also have this property. In this talk, we will highlight the recent advances towards flexible emissive displays based on OLED technology and light modulating technology that are currently funded by the government. Here, we will provide an overview of the fabrication issues that include: the substrate, active and passive matrix drivers, small molecule and polymer based emissive layers, as well as sealing. The talk will provide an overview of the different approaches taken to address these issues and what are the common issues for all technologies.
The Army Research Laboratory (ARL) conducts a broad-based optoelectronics R and D program that addresses a number of Army applications. This program covers the full range of activities from basic materials development to component development and integration into higher levels of optoelectronic functionality. This paper addresses technology areas of interest to ARL including IR detection and imaging, IR sources, ladar, multifunction optoelectronic integration, diffractive optics, optoelectronic interconnects/processing, waveguide integrated optics, wide bandgap optoelectronics, and nonlinear optics. These areas represent a cross-section of the work conducted in the Sensors and Electron Deices Directorate of ARL. Space does not allow comprehensive discussion of the R and D program each of these technology thrust ares, but references are provided in each case so that the interested reader can pursue each of these topics further.
The Army Research Laboratory has had an active program in displays for many years since all Amy systems require displays of some type. Historically the program was predominately a 6.2 to 6.3 development work. Over the last few years the emphasis has been changing to more basic work. This paper discusses our current program.
We report on a definitive demonstration of a 3D holographic display utilizing a photorefractive crystal. The resultant holographic image is viewed in real-time over a wide perspective, which can be extended by a mosaic of crystals. The image is also free from system-induced aberrations and has a uniform high quality over the entire range of FOV angles. The enhanced image quality results from the use of a phase-conjugate read beam generated from a second photorefractive crystal acting as a double-pumped phase- conjugate mirror. Multiple 3D images have been stored in the crystal via wavelength and angle multiplexing.
The nonlinear transmission of Zn:Tetrabenzporphyrin was measured in a Z-scan setup using 532 nm wavelength laser light with a 13 ns pulse duration. The excited-state absorption cross section, the excited-state refractive index cross section and the linear and nonlinear absorption contribution to a thermal image index change are discussed. The effects of fluorescence and acoustic waves on the nonlinear response of TBP have been determined. Limiter performance was modeled in an f/14 limiter and saturation effects were identified.
An optical limiter based on a large birefringence which is optically induced in bacteriorhodopsin is presented. The induced birefringence is observed to be a function of incident intensity, but saturates at a value of about 0.454 W/cm<SUP>2</SUP>. A measured value of (Delta) n of 6.6 multiplied by 10<SUP>-4</SUP> at wavelength of 514 nm is reported. The observed birefringence is found to be in good agreement with a proposed model based on vector-tensor approach.
Intensity dependent nonlinear materials placed at an intermediate focal plane in a simple two lens optical imaging system will limit radiation on a detector plane. We report the dependence of the energy and fluence limiting on aperture size, nonlinear material position, and the magnitude of the nonlinearity. The approximate performance of this same imaging system is determined for a laser source located far from the limiter. The nonlinear material requirements to limit the fluence at or below some predetermined level is determined. A dynamic range for the limiting behavior is determined which includes damage to the nonlinear material.
A photorefractive mutually pumped phase conjugator is operated in both the steady-state and transient regimes to demonstrate several important optical processing applications. While in the transient regime, or when photorefractive grating formation is taking place in the mutually pumped conjugator, cross talk is observed between the two input beams. This feature is used to demonstrate the instantaneous transfer of pictorial information from one laser beam to another and to perform the correlation of moving objects. Image transfer, optical correlation, and interferometric applications are presented. Key issues concerning the spatial resolution, time response, and Bragg condition are discussed for these applications.
Two types of optical limiting devices which have been demonstrated using photorefractive crystals are the 'beam fanning' limiter and the 'two-beam coupling' limiter. Experimental demonstrations of these two devices have revealed an interesting difference in behavior between those two limiter types. The two-beam coupling limiter is consistently faster than the beam fanning limiter for the same incident intensity. This is somewhat surprising since the beam fanning limiter is based on two-beam coupling phenomena. Our recent experiments show, however, that the relative speed of the two devices can be made more alike using a phase grating at the entrance face of the beam fanning limiter. While the phase grating scatters only about 1% to 5% of the incident light is apparently provides sufficient seeding to significantly enhance the beam fanning response time. Since the diffracted light is only about 1% the distortion to vision through the limiter due to dispersion is minimal. In the presentation we will present results from an experimental investigation of the effect of seeding on the 'beam fanning' limiter response time. In particular, we have examined the response time dependence on the intensity and direction of the seed beam. Comparison with theory will also be presented.
Optical limiting devices based on nonlinear optical (NLO) materials exhibit a throughput radiation level that is related to the magnitude of the nonlinear material parameters. In order to determine the upper bound on optical limiting performance in a variety of configurations it is necessary to establish the limitations of the NLO materials themselves. Various physical mechanisms responsible for NLO behavior in the visible spectral region are examined. Some of the largest effective nonlinearities are derived. These large nonlinear values are then compared to the nonlinearities required to protect the human eye from Q-switched visible laser pulses in a 0° field-of-view (FOV) "thin" cell limiter.
Obtaining self-pumped phase conjugation in photorefractive crystals without the use of external mirrors usually requires that the crystals exhibit significant beam fanning and have large gain-length products. Large variations in the phase conjugate reflectivity and response time can occur with changes in the incident beam location relative to the corner cube. This paper explores experimentally the dependence of the phase conjugate reflectivity and the response time on the incident beam location in a Ce-doped SBN:60 crystal. Beam erasure at selective sites within the crystal is used to determine the location of the self-organized gratings.
Thermal defocusing, nonlinear scattering and deflection, and
nonlinear quarter-wave stack switches are passive limiters that have
the ability to be extremely fast, simple in design, and require
little maintenance. In this paper we model the performance of these
devices in terms of transmission and/or throughput energy. A simple
optical design is considered in which incident radiation from
infinity is focused on the device, then recollected and reimaged on a
detector plane. Values for the effective nonlinear index of
refraction and the nonlinear time response are chosen which limit the
incident radiation to a specified optical density. The overall
performance of the protection device can then be investigated based
on the dynamic range, damage threshold, and linear transmission.