1. Presented by: Mohamed Salah the group 4290 Saint Petersburg Electro technical University "LETI" laser spectroscopy

2. Laser Spectroscopy There are several aspects of laser spectroscopy performed with molecular beams which have contributed to the success of these combined techniques. 1. Reduction of Doppler Width

3. If the source diameter is small compared with the slit width b and if b « d the flux density behind the slit B is approximately constant across the beam diameter, since The density n(v)dv of molecules with velocities v = I v I inside the interval v to v+dv in a molecular beam at thermal equilibrium, which effuses with the most probable velocity into the z direction, can be described at the distance from the source A as

4. where the normalization factor assures that the total density n of the molecules is Note that the mean flux density is If the collimated molecular beam is crossed perpendicularly with a monochromatic laser beam with frequency w propagating into the x direction, the absorption probability for each molecule depends on its velocity component vx.

5. Laser Spectroscopy of Collision Processes laser spectroscopy has already become a powerful tool for studying various kinds of collision processes in more detail. The different spectroscopic techniques illustrate the wide range of laser applications in collision physics. They provide a better knowledge of the interaction potentials and of the different channels for energy transfer in atomic and molecular collisions, and they give information that often cannot be adequately obtained from classical scattering experiments without lasers. Some techniques of laser spectroscopy, such as the method of Separated fields, coherent transient spectroscopy or polarization spectroscopy allow one to distinguish between phase changing, velocity changing, or orientation changing collisions.