This paper recalls the history of sodium guide star laser systems used in astronomy and space situational awareness adaptive optics, analyzing the impact that sodium laser technology evolution has had on routine telescope operations. While it would not be practical to describe every single sodium guide star laser system developed to date, it is possible to characterize their evolution in broad technology terms. The first generation of sodium lasers used dye laser technology to create the first sodium laser guide stars in Hawaii, California, and Spain in the late 1980s and 1990s. These experimental systems were turned into the first laser guide star facilities to equip mediumto- large diameter adaptive optics telescopes, opening a new era of Laser Guide Star Adaptive Optics (LGS AO)-enabled diffraction-limited imaging from the ground. Although they produced exciting scientific results, these laser guide star facilities were large, power-hungry and messy. In the USA, a second-generation of sodium lasers was developed in the 2000s that used cleaner, yet still large and complex, solid-state laser technology. These are the systems in routine operation at the 8 to 10m-class astronomical telescopes and 4m-class satellite imaging facilities today. Meanwhile in Europe, a third generation of sodium lasers was being developed using inherently compact and efficient fiber laser technology, and resulting in the only commercially available sodium guide star laser system to date. Fiber-based sodium lasers are being or will soon be deployed at three astronomical telescopes and two space surveillance stations. These highly promising systems are still relatively large to install on telescopes and they remain significantly expensive to procure and maintain. We are thus proposing to develop a fourth generation of sodium lasers: based on semiconductor technology, these lasers could provide a definitive solution to the problem of sodium LGS AO laser sources for all astronomy and space situational awareness applications.
Areté Associates recently developed and flight tested a next-generation low-latency near real-time dust-penetrating (DUSPEN) imaging lidar system. These tests were accomplished for Naval Air Warfare Center (NAWC) Aircraft Division (AD) 4.5.6 (EO/IR Sensor Division) under the Office of Naval Research (ONR) Future Naval Capability (FNC) Helicopter Low-Level Operations (HELO) Product 2 program. Areté’s DUSPEN system captures full lidar waveforms and uses sophisticated real-time detection and filtering algorithms to discriminate hard target returns from dust and other obscurants. Down-stream 3D image processing methods are used to enhance pilot visualization of threat objects and ground features during severe DVE conditions. This paper presents results from these recent flight tests in full brown-out conditions at Yuma Proving Grounds (YPG) from a CH-53E Super Stallion helicopter platform.
Areté Associates recently developed and flight tested a next-generation low-latency near real-time dust-penetrating
(DUSPEN) imaging lidar system. These tests were accomplished for Naval Air Warfare Center (NAWC) Aircraft
Division (AD) 4.5.6 (EO/IR Sensor Division) under the Office of Naval Research (ONR) Future Naval Capability (FNC)
Helicopter Low-Level Operations (HELO) Product 2 program. Areté’s DUSPEN system captures full lidar waveforms
and uses sophisticated real-time detection and filtering algorithms to discriminate hard target returns from dust and other
obscurants. Down-stream 3D image processing methods are used to enhance pilot visualization of threat objects and
ground features during severe DVE conditions. This paper presents results from these recent flight tests in full brown-out
conditions at Yuma Proving Grounds (YPG) from a CH-53E Super Stallion helicopter platform.
We report high power operation of a vertical external-cavity surface-emitting laser (VECSEL) operating around 1180 nm. The gain chip of the VECSEL comprises 10 strain-compensated GaInAs/GaAs quantum wells in a top-emitting configuration. A maximum output power of 23 W was achieved with a mount temperature of about 0 ‡C, and 20.5 W with the mount temperature of about 12 °C. By introducing a birefringent filter inside the laser cavity we demonstrate a tuning range of 67 nm. The gain chip was also used to construct a VECSEL for single-frequency operation. In this configuration, a maximum output power of about 11 W was recorded.
We demonstrate a dilute nitride (GaInAsN) based gain mirror capable of meeting the wavelength and linewidth
requirements for laser guide stars. The mirror was grown by molecular beam epitaxy on a GaAs(100) substrate. The heat
generated during laser operation was extracted from the active region with a wedged intracavity CVD diamond. An
intracavity birefringent filter was employed for wavelength selection and a YAG etalon for linewidth narrowing. The
laser radiation was intra-cavity frequency doubled to achieve emission at 589 nm. The frequency-doubled semiconductor
disk laser emitted a narrow linewidth beam (~20 MHz) at 589 nm. In a free-running mode, the laser emitted more than
6W of yellow-orange light with a maximum conversion efficiency of 15.5%.
Flash lidars can produce high-resolution data in all three spatial dimensions. In addition, even low repetition rate lasers result in extensive data sets. The challenge presented by these systems is: “How do we reduce the inherently large sets of data to information that is useful to the human operator.” We discuss both sensor specific and general signal-processing tools developed to render 3D lidar data in a fashion that allows man in the loop identification of targets. Data collected during an airborne field test at Redstone Aresenal Test Area Three in Huntsville using Arete Associates FLASH lidar is used to present specific examples.
Two separate data collections using Arete Associates' FLASH lidar are presented. The hardware and the experimental arrangements are discussed. An airborne data collection over military targets in clear and obscuring camouflage environments provided high-resolution three-dimensional images for combat identification purposes. In the second field test, the sensor was suspended from a crane above the ocean surface to acquire FLASH imagery of anti-landing mines and obstacles in the highly turbid surf zone environment over a wide range of surf zone conditions.
A 3D direct detection imaging laser radar was developed and tested to demonstrate the ability to image objects highly obscured by foliage or camouflage netting. The LADAR provides high-resolution imagery from a narrow pulse-width transmitter, high frequency receiver, and 3D visualization software for near-real-time data display. This work accomplished under DARPA contract number DAAD17-01-D0006/0002.
A new nitric oxide (NO) sensor is intended for use in assessment of airway inflammation with applications in asthma diagnosis and management as well as in other health care applications involving inflammation in the gastrointestinal tract and the urogenital organs. The sensor was designed to measure trace quantities of NO in air using the combination of hollow optical waveguides and quantum cascade lasers. The primary application intended is analysis of exhaled breath. The unique marriage of the components and the novel design provides for rapid response to concentration changes while maintaining sensitive measurement capabilities. We achieved a lower detectable limit of 58.8 ppb of NO in N2 with a 0-90% response time of 0.48 s. The QC laser was operated at room temperature in pulsed current mode near 5.4μm. The hollow waveguide used to make these measurements was 9m in length and the inside diameter was 1000μm. The waveguide was coiled with a 15cm radius of curvature and perforated on the interior walls of the coils to allow gas to flow into and out of the waveguide. The sensor can easily be converted to measure other gases in the midinfrared by selecting a QC laser whose output is coincident with the absorption line of interest.
The SEAL camera (SEACAM) is a small underwater imaging and ranging device that will provide a number of useful functions for the divers, such as intelligence gathering, limited nigh vision, and providing ranging information for countermining. SEACAM is designed for low-visibility missions, where 'low-visibility' refers to low diver observability, and is not a reference regarding water clarity. The camera, by virtue of the laser wavelength, is specifically made for the low-visibility mission where emission of visible light is undesirable, and is capable of working in conditions of low ambient lighting. SEACAM is a combination of a digital camera and an underwater laser range finder that allows the process range to the target to be measured simultaneously with the image. Given this measured range and the known field of view of the camera, the 'plate scale' of the image can be precisely determined, allowing for accurate estimates of the target dimensions. Upon return from the mission, the image and range data can be downloaded into a computer for rapid distribution. The camera will be magnetically and acoustically qualified for the Mine Countermeasures environment.
An ammonia monitor designed for in situ smoke stack or exhaust duct applications is discussed here. A probe composed of a diffusion cell with a protected multipass optical measurement cavity provides the optical interaction with the sample. Other components of the system include signal processing electronics and an embedded PC104 computer platform. This instrument is useful in a wide variety of ammonia monitoring and process control applications, particularly ammonia-based NOx control technologies, such as selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). The in situ design eliminates sample handling problems, associated with extractive analysis of ammonia, such as sample line adsorption and heated sample trains and cells. The sensor technology exploited in this instrument is second harmonic spectroscopy using a near infrared diode laser. Data collected during field trials involving both SCR and SNCR applications demonstrate the feasibility and robust operation of this instrument in traditionally problematic operating environments. The instrument can measure other gases by changing the wavelength, either by changing the diode operational set point or by changing the diode. In addition, with straightforward modification the instrument can measure multiple species.
Tunable diode laser absorption spectroscopy (TDLAS) shows promise for a number of environmental monitoring applications. This technique is advantageous over more classical methods because of excellent dynamic range, signal to noise ratios, and narrow bandwidth detection. With the rapid advances in the communications industry, lasers and optical components necessary for sensor technology are becoming affordable as well. One serious obstacle towards this effort is the paucity of spectroscopic data for the most useful, albeit weak, transitions near fiber optic communications wavelengths, especially at elevated temperatures. This data is important not only for species of monitoring interest, but also for those of possible interferants. In the near infrared, these are typically overtone and combination bands and hence accurate prediction of location, linestrength, and broadening coefficients is non-trivial. This is especially true for transitions arising from a highly excited rotational lower energy state. These are lines which may not be observable at room temperature but can play an important role for in-situ monitoring of a hot duct or smokestack. We have developed a system comprised of an extended cavity tunable diode laser and high temperature oven to characterize absorption spectra as a function of temperature and pressure. The experimental apparatus is described and data presented for water near 1.55 microns form 100 to 300 degrees C and 30 Torr.
Measurements made using two different types of ammonia monitors during a two-month field study in the summer of 1994 are discussed. The first instrument was a diode-laser based open path monitor designed for automated operation in an industrial environment. The second is a point monitor based on thermal decomposition of ammonia to NO and subsequent analysis by O3 - NO chemiluminescence. The two monitors provided consistent measurements of ammonia during weeks of continuous unattended operation.
A CW CO2 lidar sytem developed to determine the feasibility of using such a system for detecting and measuring low-level wind shear is discussed. The system was constructed from off-the-shelf components at a relatively low cost. Results of preliminary testing of the system are included. Wind shear measurements have been achieved but the capability of the system to measure large-scale microburst-generated wind shear has not been determined at this time.