This paper discusses revolutionary laser system architecture capable of dramatically reducing the complexity of laser systems while increasing capability. The architecture includes 3 major subsystems. The first is a phased array of laser sources. The second provides wavefront control and electronic beam steering. The third is sub-aperture receiver technology. Combining these three technologies into a new laser systems architecture results in a system that has graceful degradation, can steer to as wide an angle as individual optical phased array sub-apertures can steer, and can be scaled to high power and large apertures through phasing of a number of sub-apertures.

A review of recent advances in chemical laser technology is presented. New technology and concepts related to the Chemical Oxygen Iodine Laser (COIL), All Gas-phase Iodine Laser (AGIL), and HF Overtone Laser are discussed.

A novel dispersion-managed breathing-mode mode-locked semiconductor ring laser is studied. The working regime and pulse evolution at the key cavity points are experimentally characterized and numerically simulated. Linearly chirped, asymmetric exponential pulses are generated, suitable for external amplification and compression. The pulses are externally compressed to duration as short as 274 fs, which is within 10% of the bandwidth limit. The close agreement between the simulated and the measured results verifies our ability to control the physical mechanisms involved in pulse formation and shaping within the ring cavity.

We demonstrate an external cavity, active mode-locked GCSEL. The optical pulse duration from the actively mode-locked oscillator is 22.6ps and a 3 dB optical spectrum bandwidth is 0.07nm at 976nm. The average power from the oscillator is 0.72mW and its peak power is 108mW. The amplification characteristics of a GCSOA, optically injected with a continuously operated external cavity GCSEL, are also demonstrated. Despite the observation of lasing from the device, injection locking can be performed using an external source. At 4A peak current injection, 375mW output is achieved with 12mW injection.

Bidirectional (mutual) injection locking was demonstrated with solid-state lasers, producing significant improvements over traditional single-direction injection locking. Each laser element shares part of its output with other elements in bidirectional locking, distinct from single-direction (traditional) injection locking where one master laser provides the locking signal for a number of slaves. In a phase-locked array, the individual laser outputs add coherently, and the brightness of the entire array scales with the square of the number of elements, as if the active material diameter were increasing. Benefits of bidirectional locking, when compared to traditional injection locking, include reduced laser threshold, better output beam quality, and improved scaling capability. Experiments using two Nd:YVO4 lasers confirmed that mutual injection locking reduced lasing threshold by a factor of at least two and increased the output beam quality significantly. The injection locking effects began with 0.03% coupling between lasers and full-phase locking for coupling exceeding 0.5%. The 0.5% requirement for full phase-locking limits traditional injection-locked arrays to fewer than 100 elements, while mutually injection-locked arrays have no such limit. Mutual injection locking of an array of lasers can lead to a new architecture for high-power laser systems.

In this paper a technique for estimating a range resolved atmospheric turbulence profile statistics is investigated that uses a single laser guide star in conjunction with a Shack-Hartmann wave front sensor. The technique utilizes the fact that light passing through different layers to different wave front sensor apertures in the wave front sensor array will pass through different regions of the atmosphere whose relative distance varies as a function of distance from the laser guide star. This causes the correlation between tilts measured by each pair of wave front sensors in the array to measure different weighting of the power of the index of refraction variation in the turbulence profile as a function of altitude. This variation allows a set of linear equations to be constructed that can be solved to yield the C²_n profile. This general technique has been utilized to estimate the turbulence profile using multiple sources and apertures. This paper suggests the possibility of extending the technique to be used with a set of hardware frequently encountered in adaptive optics systems. The application of this technique at many astronomical telescopes would simply involve an additional signal processing function with no change to the optics or other hardware. Simulations performed in this paper serve to demonstrate the degree to which a single guide star could be used with an array of wave front sensors to recover the turbulence profile.

The accuracy of laser designators and range finders must be precise in order to be effective. If the operator only believes he or she is designating a target the results can be catastrophic. Range measurements for navigation may not be correct, potentially causing a collision. Reverse positioning inaccuracy may result in ordnance being misdelivered. If laser designation is incorrect, the target may be missed. Therefore in order to measure the laser designators and range finders performances and capabilities a Laser Rangefinder/Designator Beam Metrology System (LRDBMS) for beam characteristic analysis through environmental and atmospheric conditions was designed and implemented. The LRDBMS is in place at the Night Vision Electro-Optics (NVEO) Outdoor Laser Target Range located at the Naval Surface Warfare Center (NSWC) Crane Division. Atmospheric modeling software was evaluated and chosen in order to predict what is being measured by the LRDBMS.

It is well known that the transmission of an optical signal through the turbulent atmosphere results in random phase fluctuations. In turn, these random phase fluctuations impart a random frequency fluctuation onto the optical signal. As laser radar (lidar) systems rely on the evaluation of micro-Doppler frequency shifts of the reflected optical wave to determine certain target characteristics, it is critical to understand the impact of the atmospheric induced frequency fluctuations. Additionally, lidar systems used for defense applications would typically operate in moderate to strong atmospheric turbulence conditions. Hence, for such applications, it is necessary to develop models describing atmospheric induced frequency fluctuations of an optical wave that are valid in all regimes of optical turbulence. In this paper, we present preliminary results for a model of atmospheric induced frequency fluctuations for the double pass propagation problem in weak optical turbulence conditions and a possible method for extension of these results into moderate to strong turbulence conditions.

A trailer-based sensor system has been developed for remote chemical sensing applications. The detection scheme utilizes quantum cascade lasers operating in the long-wave infrared. It has been determined that atmospheric turbulence is the dominating noise source for this system. For this application, horizontal path lengths vary from several hundred meters to several kilometers resulting in weak to moderate to strong turbulence conditions. Field experiments have simultaneously monitored meteorological and atmospheric quantities during remote sensing in order to better understand the impact of turbulence on horizontal beam propagation. A numerical model has been developed to simulate the performance of the system and comparisons between simulation and experiment have been encouraging.

The role of the Advanced Air Transportation Technologies program undertaken at the NASA Glenn Research Centers has been focused mainly on the improvement of air transportation safety, with particular emphasis on air transportation communication systems in on-board aircraft. The conventional solutions for digital optical communications systems specifically designed for local/metro area networks are, unfortunately, not capable of transporting the microwave and millimeter RF signals used in avionics systems. Optical networks capable of transporting RF signals are substantially different from the standard digital optical communications systems. The objective of this paper is to identify a number of different communication link architectures for RF/fiber optic transmission using a single backbone fiber for carrying VHF and UHF RF signals in the aircraft. To support these architectures, two approaches derived from both hybrid RF-optical and all-optical processing methodologies are discussed with single and multiple antennas for explicitly transporting VHF and UHF signals, while the relative merits and demerits of each architecture are also addressed. Furthermore, the experimental results of wavelength division multiplexing (WDM) link architecture from our test-bed platform, configured for aircraft environment to support simultaneous transmission of multiple RF signals over a single optical fiber, exhibit no appreciable signal degradation at wavelengths of both 1330 and 1550 nm, respectively. Our measurements of signal to noise ratio carried out for the transmission of FM and AM analog modulated signals at these wavelengths indicate that WDM is a fiber optic technology which is potentially suitable for avionics applications.

Shipboard infrared search and track (IRST) systems can detect sea-skimming anti-ship missiles at long ranges. Since IRST systems cannot measure range and velocity, they have difficulty distinguishing missiles from slowly moving false targets and clutter. ARL is developing a ladar based on its patented chirped amplitude modulation (AM) technique to provide unambiguous range and velocity measurements of targets handed over to it by the IRST. Using the ladar's range and velocity data, false alarms and clutter objects will be distinguished from valid targets. If the target is valid, it's angular location, range, and velocity, will be used to update the target track until remediation has been effected. By using an array receiver, ARL's ladar can also provide 3D imagery of potential threats in support of force protection. The ladar development program will be accomplished in two phases. In Phase I, currently in progress, ARL is designing and building a breadboard ladar test system for proof-of-principle static platform field tests. In Phase II, ARL will build a brassboard ladar test system that will meet operational goals in shipboard testing against realistic targets. The principles of operation for the chirped AM ladar for range and velocity measurements, the ladar performance model, and the top-level design for the Phase I breadboard are presented in this paper.

A megawatt-class high energy laser aboard a Navy ship could provide effective self defense against modern anti-ship missiles. The free electron laser is a candidate for use in this mission, and has several advantages over chemical lasers, which have been previously considered. One obvious advantage is wavelength tune-ability of teh FEL-allowing tuning of the laser wavelength to an atmospheric spectral window of minimum absorption. This study reports on analysis performed to select optimum wavelengths for a ship-based FEL in consideration of atmospheric effects. We examine atmospheric absorption, scattering, trubulence, and thermal blooming, and compare their relative importance in optimizing power in the bucket on target for representative scenarios. We also examine the issue of thermal blooming caused by atmospheric aerosol absorption, and examine the relative absorption of open-ocean vs continental aerosols. We find excellent propagation results at 1.625 and 1.047 microns.

The signal-to-noise power ratio parameter of coherent ladar systems operating within the atmosphere and including atmospheric scintillation effects is modeled. Previously published round-trip geometry ladar data of the variance of the normalized-irradiance as a function of the one-way path integral Rytov parameter are utilized to estimate a signal-tonoise power ratio. However, these data were taken in the strong signal case where local-oscillator-laser noise was negligible. A model is proposed to combine the local-oscillator-laser produced noise, a zero-mean wideband-Gaussian random process corresponding to normal coherent ladar operation, with the scintillation produced by round-trip turbulence based on a calculation of the one-way path-integral Rytov parameter. Close agreement with Shapiro's 1981 analysis is found, provided one modifies the Shapiro formulation to account for scintillation saturation.

Laser weapon systems would be significantly enhanced with the addition of high altitude or space-borne relay mirrors. Such mirrors, operating alone with a directed energy source, or many in a series fashion, can be shown to effectively move the laser source to the last, so-called fighting mirror. This “magically” reduces the range to target and offers to enhance the performance of directed energy systems like the Airborne Laser and even ground-based or ship-based lasers. Recent development of high altitude airships will be shown to provide stationary positions for such relay mirrors thereby enabling many new and important applications for laser weapons. The technical challenges to achieve this capability are discussed.