Erbium doped YAG is an intriguing laser material which lases directly at 1645nm when pumped at either 1473nm or
1532nm, all of which are in the eye-safe band. However, a laser made from this material is not particularly
straightforward to design. Er:YAG is a quasi-three-level system, which leads to strong temperature dependence.
Perhaps more importantly, a strong up-conversion process, which is dopant concentration dependent, effectively
produces a pump intensity dependence in the saturation intensity and other laser parameters. We present a detailed
study of the absorption coefficient and the gain as a function of the pump intensity, dopant concentration and crystal temperature. The results of this study will allow us to optimally design the laser.
Erbium doped YAG, lasing at 1645 nm from a 1532 nm pump, is an intriguing alternative to wavelength shifted 1-micron lasers for eye-safe applications. In this paper, we will report on an end-pumped Er:YAG laser that employs diamond disks for heat extraction. Using an alternating arrangement of diamond and Er:YAG thin disks, heat flows from the gain material to the diamond along the optical axis and is then radially transmitted to a circulating cooling fluid at the perimeter of the diamond disks. This architecture allows larger diameter disks or rods to be used than conventional radial cooling architectures, thus allowing for higher powers through area scaling. This architecture also provides better beam quality for a given pulse energy. We have demonstrated excellent beam quality (M2=1.3) from a 10-Watt Er:YAG laser. We will also report on results of Q-switching and oscillator-amplifier experiments in a study of the well-known up-conversion process for relatively low dopant concentrations (0.5%-1.0% a.w. of Erbium).
Scaling studies of a Cr:LiSAF power oscillator are being performed and 80W average output power has been achieved at 10Hz repetition rate using a newly designed transverse flow cell. An SBS phase conjugate system using Fluorinert FC-75 has been set up and reflectivity measurements indicate very good fidelity with reflectivities >60%, at pulse energies of less than 1J.
This report briefly reviews the development, capabilities, and current status of pulsed high-power coherent CO2 laser radar systems at the Maui Space Surveillance System (MSSS), HI, for acquisition, tracking, and sizing of orbiting objects. There are two HICLASS systems, one integrated to the 0.6 m Laser Beam Director and one just integrated Summer 2000 to the 3.7 m Advanced E-O System (AEOS). This new system takes full advantage of the large AEOS aperture to substantially improve the ladar range and sensitivity. These improvements make the AEOS HICLASS system potentially suitable for tracking and characterization experiments of small < 30 cm objects in low-earth-orbits.
The optical quadrature imaging technique, as derived and extended from microwave and laser radar quadrature detection techniques, provides an efficient method for obtaining phase information from a sample that has little or no amplitude contrast. We are able to resolve internal structures of a sample that are defined by relatively small refractive index differences without the use of dyes or stains, while using much lower light levels than conventional techniques. We have constructed a prototype system for imaging microscopic phase- only objects. In this paper, we present its capabilities, as well as the imaging and reconstruction methods used to obtain quantitative information about a sample.
A concept is described for a Doppler Lidar capable of three- dimensional measurements. The concept is based on conventional line-of-sight lidar with multiple beams, each slightly displaced with respect to the other. A quadrature detection technique is used to provide sign determination so that three- dimensional velocities can be resolved unambiguously.
We have investigated the use of acoustic energy produced by a pulsed CO2 laser to detect objects underwater or buried in sand. The CO2 laser produced 150 mJ pulses of duration 100 ns. The resulting acoustic pulses were detected with an audio microphone with a response to 15 kHz or a PZT transducer with a resonant frequency at 28 kHz. With the laser incident on the surface of a water-filled tank, acoustic echoes were observed from the tank walls and from objects in the tank. For objects buried in sand, changes in the acoustic lineshape related to the presence of subsurface objects were observed. Analysis of the data to extract clear signatures of the mine are in progress.
KEYWORDS: Microwave radiation, Thermography, Absorption, Temperature metrology, Sensors, Data fusion, Fusion energy, Land mines, Solar energy, Infrared cameras
No single sensor modality will solve the problem of detecting small, buried objects in soil in the presence of typical clutter. Techniques involving fusion of data from multiple sensors can improve detection statistics. At the next level of complexity is multi-modal sensing in which an excitation with one modality is detected by another. Here we consider one such example, microwave heating of the soil followed by infrared imaging. The technique promises to produce signatures of buried objects which have contrast with respect to the surrounding soil in (1) absorption at the microwave frequency resulting in a change in the amount of energy absorbed, (2) dielectric constant resulting in alteration of the field distribution in the soil, or (3) thermal properties resulting in changes in the heat distribution. Indirect detection may be possible, through changes in the microwave or thermal properties of the soil caused by disturbance during placement of the object, or caused by changes in the soil properties resulting from alterations in water content caused by the object. We discuss wavelength selection, expected sensitivity, and techniques for enhancement of the signal, as well as overall system requirements, and will show some preliminary results.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.