Optical system and method for gas detection and monitoring

A free-space optical path of an optical interferometer is disposed in an environment of interest. A light beam is guided to the optical interferometer using a single-mode optical fiber. The light beam traverses the interferometer's optical path. The light beam guided to the optical path is combined with the light beam at the end of the optical path to define an output light. A temporal history of the output light is recorded

Laser Propulsion Standardization Issues

It is a relevant issue in the research on laser propulsion that experimental results are treated seriously and that meaningful scientific comparison is possible between groups using different equipment and measurement techniques. However, critical aspects of experimental measurements are sparsely addressed in the literature. In addition, few studies so far have the benefit of independent confirmation by other laser propulsion groups. In this paper, we recommend several approaches towards standardization of published laser propulsion experiments. Such standards are particularly important for the measurement of laser ablation pulse energy, laser spot area, imparted impulse or thrust, and mass removal during ablation. Related examples are presented from experiences of an actual scientific cooperation between NU and DLR. On the basis of a given standardization, researchers may better understand and contribute their findings more clearly in the future, and compare those findings confidently with those already published in the laser propulsion literature. Relevant ISO standards are analyzed, and revised formats are recommended for application to laser propulsion studies

CO2 Laser Ablation Area Scaling and Redeposition on Flat Polyoxymethylene Targets

One of the remaining subjects of interest for laser ablation propulsion study is whether special benefits or challenges exist when applying a particularly large or small laser spot area to a target. This subject is of high importance for topics including laser removal of space debris, micropropulsion, and design of laser propulsion vehicles. Analysis of spot area-dependent effects is complex since ablation phenomena differ between atmosphere and vacuum conditions. Progress has also been impeded by the difficulty of setting control parameters (particularly fluence) constant while the spot area is adjusted. It is virtually impossible for one group to address small- and large-area effects using a single high-power laser system. Recent collaborative experiments using 100-J class and 10-J class CO2 lasers have advanced the understanding of laser propulsion area scaling. Experiments were conducted below the threshold for plasma formation. The dependence of various laser propulsion parameters on the laser spot area has been investigated within areas covering approximately 0.5-50 cm2 on the target

Update on CO2 Laser Ablation of Polyoxymethylene

Polyoxymethylene (POM) propellants have been studied since the 1970's, and perhaps represent the most promising match of a propellant to the CO2 laser for laser propulsion studies. Applications range from ground-launch of laser propulsion vehicles at atmospheric pressure to spacebased laser ablation propulsion microthrusters. In this paper we broadly update the state of understanding of CO2 laser ablation of POM based on new experiments conducted in Japan and Germany, with a focus on the basic physics of ablation of flat POM targets. Measurements using 10 J-class and 100 J-class lasers are compared to previous literature results for ablation of POM. Emphasis is placed on the influence of control parameters on ablation, especially the incident laser fluence and ambient pressure. New results highlight the influence of the ambient pressure on ablation physics from the vaporization threshold to the plasma regime, and clarify the role of the fluence in determining ablation behavior in air and vacuum environments. Imparted impulse and ablated mass were measured at the target using piezoelectric force sensors, impulse pendulums, and scientific balances. The new experimental investigations cover orders of magnitude in fluence (10E-2 to 10E3 J/cm2) and ambient pressure (10E-3 to 10E5 Pa)

Experimental Determination of the Impulse Coupling Coefficient - Standardization Issues

In research on beamed energy propulsion, the momentum coupling coefficient cm is a central figure of merit to characterize a propulsion system. Basically, the determination of cm is based on the measurement of imparted impulse and laser pulse energy. Nevertheless, the knowledge of laser pulse length, laser spot area and ablated mass is of great importance for the comparability of experimental results in laser ablative propulsion. The use of a great variety of measurement techniques for these parameters throughout the scientific community implies the risk of misunderstandings and might impede the comparability of results. In this paper, we present critical issues concerning the measurement of the aforementioned key parameters with respect to possible standardization issues. As an example, a simple laser propulsion experiment will be presented and compared with an experimental model from a different research group