Possible Condensation Laser

1. 拟进行的研究摘要：实验将包括将各种气体混合物暴露在源室的电晕放电中，然后将被激发的气体通过一个小喷嘴膨胀到真空中作为超音速射流。特别令人感兴趣的是那些激发态以红外线辐射的物质，如CO和CO2。它们的辐射将通过傅里叶变换红外光谱法和全辐射探测器进行分析。在一些初步实验中，当源气体的初始温度和压力达到预期在自由射流膨胀期间会发生冷凝时，辐射强度增加了五倍之多。由此产生的问题是，这种观测到的“超辐射”是否由于基态分子的聚集引起的种群反转，这将改变它们的吸收波长，从而使它们不能吸收受激发单体辐射的光子。研究的目的是确定在什么种类和什么条件下可以产生超辐射，潜在机制的性质，以及该机制是否为红外系统中有用的激光器提供了有效的新方法。2. 新颖性：激光操作的必要条件是当受激分子辐射光子时，处于高激发态的分子数量密度超过处于低激发态的分子数量密度。在激光系统中，已经使用了许多种工艺来填充上态和/或去填充相应的下态。据我们所知，反转以前还没有通过使用冷凝来减少低态的人口来实现。原则上，它应该是有效的，用超音速自由射流进行的初步实验表明，它可以发生在含有振动激发态的气体的快速绝热膨胀中。3. 技术影响：初步实验表明，含有振动激发CO和CO2的自由射流产生了显著的超辐射。暂定的解释是由于分子在较低的状态下聚集或凝聚而导致的人口反转。如果这一结论被提议的研究证实，那么发展新的“冷凝激光”系统的道路似乎是开放的。由于这种方法应该适用于几乎任何具有红外活性的气体物种，因此有广泛的激光系统覆盖大部分红外光谱的前景。相对复杂的分子应该具有可调性。量子效率应该很高，因为较低的状态必须有很少或没有剩余的内能才能凝结。

1. Summary of Proposed Research: Experiments to be carried out will consist in exposing various gas mixtures to a corona discharge in a source chamber and then expanding the excited gas through a small nozzle into vacuum as a supersonic jet. Of particular interest are species whose excited states radiate in the infrared such as CO and CO2. Their radiation from the jet will be analyzed by Fourier Transform Infrared Spectrometry as well as by total radiation detectors. In some preliminary experiments the intensity of the radiation showed as much as a fivefold increase when the initial temperature and pressure of the source gas were such that condensation would be expected during the free jet expansion. The question thus arises as to whether this observed "superradiance" was due to a population inversion caused by clustering of the ground state molecules which would shift their absorption wavelength so that they could not absorb photons radiated by excited monomers. The objective of the research is to determine with what species and under what conditions the superradiance can be made to occur, the nature of the underlying mechanism, and whether that mechanism offers an effective new approach to useful lasers in the infrared regime. 2. Novelty: The sine qua non of laser operation is a population inversion in which the number density of molecules in an upper excited state exceeds the number density in the lower state produced when the excited molecule radiates a photon. Many kinds of processes have been used to populate an upper state in a laser system and/or to depopulate the corresponding lower state. To our knowledge inversions have not previously been achieved by the use of condensation to depopulate the lower state. In principle it should work and preliminary experiments with supersonic free jets indicate that it can occur in rapid adiabatic expansion of a gas containing vibrationally excited species. 3. Technological Impact: Preliminary experiments have shown remarkable superradiance from free jets containing vibrationally excited CO and CO2. The tentative explanation is a population inversion due to clustering or condensation of molecules in the lower state. If this conclusion is confirmed by the proposed research, the way would seem open for the development of new "condensation laser" systems. Because this approach should be applicable to almost any gaseous species that is infrared-active, there looms the prospect of a wide range of laser systems covering a large part of the infrared spectrum. Relatively complex molecules should offer tunability. Quantum efficiencies should be high because the lower state must have little or no remaining internal energy in order to condense.