The Nautilus Project was started in 1995 as a joint US-Israel feasibility study for using laser systems to defend against short-range artillery rockets. It has now matured into a successful laser weapon demonstration program - the Tactical High Energy Laser (THEL) Advanced Concept Technology Demonstration (ACTD) Program. By now the THEL Demonstrator has engaged and destroyed a large number of artillery rockets in mid-flight in an extended series of demonstration tests at the US Army's White Sands Missile Range in New Mexico. The THEL ACTD hardware and development process are described in this paper, as well as the major test results. The paper also describes the operational concept for a deployed THEL weapon system and some possible growth paths for the THEL ACTD Program.

The US Air Force Airborne Laser (ABL) is an airborne, megawatt-class laser system with a state-of-the-art atmospheric compensation system to destroy enemy ballistic missiles at long ranges. This system will provide both deterrence and defense against the use of such weapons during conflicts. This paper provides an overview of the ABL weapon system including: the notional operational concept, the development approach and schedule, the overall aircraft configuration, the technologies being incorporated in the ABL, and the risk reduction approach being utilized to ensure program success.

The Space Based Laser (SBL) program is concerned with both near-term feasibility of space lasers and also the desired operational capability for a robust SBL constellation. For the near term system, we have defined an Integrated Flight Experiment (IFX) that will integrate a high power laser device, a beam control system, and a large beam director, performing a lethal engagement against a boosting missile in the 2010-2014 time period. For the operational system, the program was conducted its Affordability and Architecture Study (AAS) for Dr. Jacques Gansler (former USD(AT&L)). We arrived at a particular set of solutions for a prescribed threat. These solutions include both pure SBL constellations and also combinations of SBL satellites and space-based relay mirrors (SBM). We also considered Air Borne Lasers (ABL) and Ground Based lasers (GBL) as complements to the SBL and SBM. In this paper, we describe the current status of both the IFX program, which is the principal recipient of current funding, and also a nascent SBL Technology program to address the needs of the operational system. For the technology program, we analyzed the specific technology areas we need to develop in order to realize the most pay off for operational SBL systems.

We present a review of our experimental studies on picosecond UV (248.6 nm) filaments and give a motivation for scaling them to longer pulsewidths. An analytical solution for the propagation of nanosecond UV filaments shows their feasibility for directed energy applications.

On-orbit servicing (OOS) is growing in importance for the sustainment of certain satellite systems. Although it is more economical to replace satellites in many cases, OOS could be beneficial, or even critical, for more expensive satellites such as Space-Based Laser and constellations such as the Global Positioning System. Some future OOS missions including refueling and modular component replacement will be highly autonomous, but there will still be a need for humans to supervise and to recover when unexpected situations arise. Non-routine tasks such as damage repair or optics cleaning will likely require a more significant level of human control. The human interfaces for such activities can include body tracking systems, three-dimensional audio and video, tactile feedback devices, and others. This paper will provide some insights into when and at what level human interaction may be needed for OOS tasks. Example missions will be discussed and the argument will be made that human interfaces are important even for primarily autonomous missions. Finally some current research efforts within NASA, academia and the military will be discussed including research being conducted in the Air Force Research Laboratory at Wright-Patterson Air Force Base.

Space based defense systems, such as a Space Based Laser (SBL), and space based surveillance systems share a common objective: extremely high resolution Line of Sight (LOS) target imaging. In order to achieve the mission objectives, their beam control subsystem must provide precise LOS pointing and tracking capabilities with suppression of LOS jitter. Draper Laboratory has developed concepts and instrumentation that address these needs based upon a stabilized inertial platform mechanization that holds a collimated light source, called the Inertial Pseudo Star Reference Unit (IPSRU). This paper describes the original IPSRU design and a design concept for a new High Performance version of the IPSRU system (HP-IPSRU) that meet the jitter stabilization needs of the SBL. The IPSRU provides an inertially stabilized optical probe beam that provides a precise pointing and tracking reference with nanoradian jitter performance. The IPSRU serves as a master reference for stabilizing imaging and weapon system pointing and tracking. This paper describes the IPSRU system, its measured error allocation and integrated performance. It presents the error budget required to achieving the 5 nrad rms jitter stabilization performance projected to be necessary for an operational Space Based Laser system. A conceptual design for the HP-IPSRU is presented.

This paper describes a high-energy laser (HEL) concept based on a disk-type solid-state laser operating in active mirror mode. The gain medium disks have high-performance real-time cooling that allows the laser to operate continuously. This configuration of the laser shows excellent scalability to high-average power required for directed energy applications and can be integrated into a simple, compact, lightweight, and affordable unit. The paper also discusses engineering concepts for integrated HEL, power-size-weight scaling model, as well as options for prime power and thermal management.

This paper describes a method of enhancing coherence and intensity of a broad-area laser array. An experimental scheme has been proposed to injection lock a single or multiple broad-area high-power lasers in a commercially available 19-laser array driven by a common current source. We experimentally demonstrate both the injection locking of each individual broad-area laser and the simultaneous injection of two broad-area lasers in a 19-laser array using a single-mode laser as the source of injection. The method and required conditions for the simultaneous locking of all 19 lasers have been discovered from the experimental results.

A new polarization optical element - a parallel axicon which is a cylinder whose face surfaces have a conical form with identical vertex angles and are parallel relative to each other - is proposed. It allows for compensation of thermally induced birefringence in laser rods of master oscillators and amplifiers. The optical scheme that we suggest consists of a quarter-wave plate, laser rod, 45 degree reciprocal rotator, parallel axicon and mirror. The parallel axicon operates as a quarter-wave plate whose axis inclination angle coincides with polar angle. As a result, after two passes through the whole scheme the radiation resumes its linear polarization, e.e., depolarization in the laser rod is totally compensated. In this work we discuss in detail numerous aspects of the proposed technique, including advantages and disadvantages of this technique in comparison with other methods. The proposed technique for compensation of birefringence in AE may find a broad application in powerful laser oscillators and amplifiers based on Nd:YAG and other isotropic active media.

This paper gives the history of the invention and development of early high power lasers, to which the author contributed and had personal knowledge. The earliest hint that a high power laser could be built came from the electric CO₂-N₂-He laser of Javan. It happened that the director of the Avco-Everett Research Laboratory had written his Ph.D. dissertation on the deactivation of the vibrational excitation of N₂ in an expanding flow under Edward Teller, then at Columbia Univ. The director then started an in-house project to determine if gain could be achieved in a mixture similar to Javan's by means of a shock tunnel where a shock heated mixture of N₂, CO₂, and He gas was expanded through a supersonic nozzle into a cavity. This concept was named by the author as the gasdynamic laser (GDL). The paper traces the history of the initial gain measurements, the Mark II laser, the RASTA laser, the Tri-Service laser, its troubles and solutions, the United Technology's XLD gasdynamic laser, and their ALL laser. The history of the coastal Crusader will also be mentioned. Also discussed are the early experiments on a combustion-driven chemical laser, and its subsequent rejection by the director.

The advent of the DF chemical laser in the early 1970s provided the Navy with a laser source that suffered less from atmospheric absorption than did CO₂. This technology was systematically scaled up in power and integrated with beam control systems to support assessment as a future weapon for fleet defense. The Navy-ARPA Chemical Laser (NACL) was mated with the Navy Pointer Tracker at TRW's San Juan Capistrano facilities in the 1975-1978 time frame. This was the Navy's initial integrated HEL system test-bed and was used to provide the first demonstrated kill of an operational missile in 1978. This was followed by the Mid-Infrared Advanced Chemical Laser (MIRACL) and the SeaLite Beam Director (SLBD) which provided the nation's first (and only) megawatt class HEL test-bed. They were integrated in the mid 1980s at the Army's High Energy Laser System Test Facility at White Sands Missile Range, New Mexico. Following integration, extensive tests were conducted in the areas of high power optical components and beam path conditioning, beam control techniques, high power propagation, target damage and vulnerability, and target lethality.

A technique for modeling the effect of illuminator partial coherence on target imaging and optical tracking is discussed. Computer simulations of imaging and tracking through atmospheric turbulence show that it is important to account for illuminator partial coherence if one is interested in accurately modeling the effects of turbulence on optical tracking.

This study extends branch point tolerant phase reconstructor research to examine the effect of finite time delays and measurement error on system performance. Branch point tolerant phase reconstruction is particularly applicable to atmospheric laser weapon and communication systems, which operate in extended turbulence. We examine the relative performance of a least squares reconstructor, least squares plus hidden phase reconstructor, and a Goldstein branch point reconstructor for various correction time-delays and measurement noise scenarios. Performance is evaluated using a wave-optics simulation that models a 100km atmospheric propagation of a point source beacon to a transmit/receive aperture. Phase-only corrections are then calculated using the various reconstructor algorithms and applied to an outgoing uniform field. Point Strehl is used as the performance metric. Results indicate that while time delays and measurement noise reduce the performance of branch point tolerant reconstructors, these reconstructors can still outperform least squares implementations in many cases. We also show that branch point detection becomes the limiting factor in measurement noise corrupted scenarios.

A fast electron energy spectrometer has been built using a photodiode array measuring the backward optical transition radiation from a thin film of aluminum. The resolution of the electron energy spectrometer is about 0.2% with a time resolution of 50 ns. The maximum energy spread that can be measured is 6.4%. We present the measurements of the time-resolved electron beam energy spectrum on the Mark III linear accelerator at Vanderbilt University, while lasing at different wavelengths and while not lasing. We also discuss the effects of different parameters, such as cathode heating, alpha magnet strength and RF phase, on the electron energy spectrum and optical spectrum. The diagnostics of time-resolved electron energy spectrum and time-resolved laser spectrum provide the technology to understand the physical process of the FEL interaction. Based on these diagnostics, the FEL facility can realize some special modes of operation, such as macropulse chirping and macropulse two color lasing.

The mechanism of nonlinear harmonic generation in the exponential gain regime, which is driven by bunching at the fundamental wavelength, may provide a path toward both enhancing and extending the usefulness of an x-ray free- electron laser (FEL) facility. Related exotic generation schemes, which exploit properties of harmonic production in various undulator topologies, have been discussed both in the past and more recently. Using three different numerical simulation codes, we explore the possible utility of such schemes (e.g., harmonic afterburners and biharmonic undulators) at future light source facilities.

Lasing at high power in FELs has been achieved so far only with a near-concentric resonator [1]. Though this design can scale up to quite high power, it is ultimately limited by the mirror steering stability as the resonator design approaches con-centricity. This constraint may be avoided by using a near-confocal resonator operated in a ring configuration. It is found that, if a small amount of gain focusing is present, the near-confocal resonator eigenmodes are modified such that the lowest order mode collapses around the electron beam and is large in the return (non-focusing) direction. This eigenmode is stable and is relatively insensitive to changes in the mirror radii of curvature and the strength of the electron beam focusing. This paper will present the theory of this new concept.

All space activities rely completely on rockets to get into space. Advanced propulsion systems are being examined by NASA and others but few if any of these technologies, even if perfected, can provide the high-volume, low-cost transportation system required for future space activities mankind hopes for. A system with the required traits is the space elevator. The space elevator, a cable that can be ascended by mechanical means from Earth to space, would reduce the cost of getting into space by a factor 100 or more while increasing launch capabilities dramatically. Under a NIAC grant we have laid the technical groundwork by examining all aspects of a first elevator. For a cost of $40B the first space elevator could provide low-risk, inexpensive access to space within the next 15 years. A free-electron laser power beaming system is critical to the success of the space elevator, no other system has the performance required to provide power to the climbers. Using the free-electron laser power beaming system the space elevator could efficiently provide inexpensive access to space for placing satellites, human colonization and placement of space-based solar power satellites that could provide large quantities of renewable clean power.

The space elevator, a cable with one end attached to Earth and the other 100,000 km up in space that can be ascended by mechanical climbers, is a revolutionary system for carrying satellites into space. A 20.000 kg-capacity space elevator appears feasible with developing technologies at a cost of $40B. The basic design and implementation of the elevator have been worked out and many of the components are in use in other programs. The ComPower laser beaming design (free- electron laser and adaptive optics) has the performance required for the critical delivery of power to the climbers. With system designs in hand the next step is to perform a feasibility test of the overall system. One possible test utilizes a high-altitude balloon, carbon nanotube composite tether, protytpe climber, and laser power beaming system. A free-electron laser beam is directed to the climber using a lightweight composite mirror system with adjustable beam diameter. The climbers will ascend the tether to a 600 m altitude demonstrating the performance of the climber, power delivery and laser beaming system along with interactions of all the components. Combining this test with several others being conducted should demonstrate the viability of the space elevator.

The spatial light modulator (SLM) can be used to alter the phase of the wave front to achieve a deflection or a change in the shape of a laser beam. In this study a commercial nematic zero-twist liquid crystal SLM was evaluated. SLMs can be operated to produce pure phase modulation necessary for beam steering. For liquid crystals the relation between applied voltage and phase modulation is highly non-linear due to the relation between the voltage driven molecular tilt angle and extraordinary refractive index. To compensate for this effect we optimized and examined look-up tables (LUT) that realize the inverse of the phase response. It was found that the factory LUT improved the power ratio between the zero order and the first order peaks five times compared to the case without using an LUT, however, further improvement of this ratio of two was reached using an LUT optimized from the measured phase response of the SLM. The discrete phase modulation results in a stepped, non-ideal blazed grating that alters the relative power of the available steering angles. To obtain optimal performance these effects must be analyzed for different bit depths and preliminary results of such quantization effects are discussed.

In order to increase the plasma production efficiency in the laser triggered lightening experiment, it is proposed that a hyper-velocity micro-particle flow produced by a chemical explosion shall be used along the laser beam path. A preliminary experiment to verify the proposal has successfully been done in the laboratory using 100 J 80 nsec CO₂ laser pulse.

Laser applications in science and technology are based on the special properties of laser radiation, such as monochromaticity, coherence, beam concentration and high power density. Since the laser was discovered, an ever increasing number of applications have been found for it in the most diversified fields. Despite this, its wide possibilities are still by no means fully known or exhausted. Further development is continually taking place in the design of new systems. The generation of the photons is in itself an optic-electronic process. The trajectory of the laser beam is linear. It could be modified by a lens or by a mirror. We built some devices, in order to know how a laser beam could be partially deviated by a divergent nozzle. We began with a simple device, but at present we built a mono-module device, which is safer concerning the positioning errors.

SLAC E158 is an experiment to make the first measurement of parity violation in Moller scattering. The left-right cross-section asymmetry in the elastic scattering of a 45-GeV polarized electron beam off unpolarized electrons in a liquid hydrogen target will be measured to an accuracy of better than 10^-8, with the expected Standard Model asymmetry being approximately 10^-7. An intense circularly polarized laser beam for the polarized electron source is required with the ability to quickly switch between left and right polarization states with minimal left-right asymmetries in the parameters of the electron beam. This laser beam is produced by a unique SLAC-designed, flash-lamp pumped, Ti:Sapphire laser. We present this laser system design and initial results from recent commissioning runs.

A use of the energy transmission system is proposed to supply the scientific rover to confirm the existence of ice on the moon at the bottom of craters in the lunar polar region, where no sun light reaches at all through the year and it is a cryogenic environment. A small system model has been fabricated that it is principally possible. A full size rover model is now going on and 100 m energy transmission experiment will be done soon. Major technological problems to be solve to realize the system in the actual lunar exploration is also discussed.

High power laser based electro-optic sensor systems are generally bulky. Currently, several of these systems have to be located near exit apertures on airborne platforms due to lack of high damage resistant flexible optical conduits offering high mode fidelity and transmission efficiency. In several cases, system functionality has to be scaled down in a space-constrained environment. Coherent Technologies, Inc. has developed flexible, efficient, metallic rectangular hollow waveguides for use with high-energy laser systems such that they can be re-located to a convenient, safe, and protective location. These ribbon-like waveguides provide >96%/m transmission efficiency with near diffraction-limited performance and high mode fidelity besides transporting high-energy optical radiation. In this paper, damage threshold measurement carried out using aluminum based rectangular hollow waveguides is reported. Measurements at 2 micrometers and 10.6 micrometers wavelengths in 1-m long waveguides with aperture heights of 100 to 250 micrometers have been performed. Damage thresholds greater than 1 GW/cm² has been measured at 2 micrometers wavelength. Being thin and flexible, these waveguides are low cost, easy to fabricate, and are amenable for integration into fuselage of an airplane. It is anticipated that distributed aperture coherent ladar systems and high power optical directed energy on space/airborne platforms would benefit from this technology.