Laser absorption/gain experiments

The earliest experiments with lasers in absorption spectroscopy were performed with the high-gain infrared line X = 3.39p of the He-Ne laser the first gas laser Several authors Miscovered that this laser line is absorbed by many hydrocarbon molecules, causing a vibrational-rotational transition in a band which belongs to the excitation of a C-H stretching vibration . ... 

We report on saturated absorption experiments in Na2> realized with a tunable and stabilized argon laser. These experiments provide both spectroscopic and physical results, which help in understanding the behavior of optically pumped alkali dimer lasers. We briefly describe a new double resonance experiment which enables us to study the gain line-shapes of the dimer laser and to demonstrate the backward-forward gain competition. 

In other words, the Stokes wave experiences an exponential gain constant (if jV, > N2) that is proportional to the incident laser intensity. If this gain is larger than the loss at owing to absorption, random scatterings, and so on experienced by the Stokes wave, it is possible to have laser oscillations (i.e., the generation of Stokes lasers). Such a process is called stimulated Raman scattering. 

With the development of the first chemical laser sources it became possible to use the lasers themselves to obtain the specific rate constant data formerly available only from the infrared chemiluminescence experi-ments. " Some very useful techniques have been developed by Pimentel and co-workers for the determination of the partitioning of the energy release of chemical reaction among the vibrational levels of diatomic reaction products/ These techniques are based on the relationship between gain or absorption and the ratio of vibrational populations on a given vibration-rotation transition. These methods were originally developed for the study of reactions of interest for chemical lasers however, they have been generalized to include many other reactions which do not provide useful population inversions. 

---