Construction of coherent antistokes Raman spectroscopy (CARS)

Coherent Antistokes Raman Spectroscopy (CARS) has been built. It consists of a Raman cell, which is filled with CO2 gas at 5 atm pressure and a frequency doubled Nd-YAG laser pumped dye laser. The two beams are focused by means of a bi-convex lens into Raman cell. The Antistokes signals (CARS signals) are generated due to Four-wave mixing process. The antistokes signals were directed to monochrometer entrance slit by prism . The signals are detected by photomultiplier detector which is fixed on the exit slit and connected to data acquisition card located inside the computed case. The dye laser frequency has to be tuned to satisfy the energy difference between the ν1 beam (Nd- YAG laser beam) and the ν2 beam (the stokes beam or the dye laser beam) exactly corresponds to a vibrational - rotational Raman resonance (ν2 - ν1 = νM) in the 12CO2 or 13CO2 molecule, then the antistokes signals (ν3) will be generated. The spectra of the CARS signals have been recorded to determine the isotope shift of 12CO2, 13CO2, which is 18.3 cm-1. (author)