Cavity-enhanced phase-matched coherent Stokes Raman spectroscopy.

Area of Science:

• Spectroscopy
• Quantum Optics
• Chemical Analysis

Background:

• Standard Raman spectroscopy suffers from low sensitivity due to small scattering cross-sections.
• Coherent Raman spectroscopy techniques aim to overcome these limitations.
• Optical enhancement cavities can amplify weak spectroscopic signals.

Purpose of the Study:

• To develop and demonstrate an ultrasensitive detection method for trace gaseous molecules.
• To intensify Raman signals using phased-matched coherent Stokes Raman scattering within a high-finesse optical cavity.
• To quantify the signal enhancement compared to spontaneous Raman scattering.

Main Methods:

• Utilizing phased-matched coherent Stokes Raman scattering.
• Employing a macroscopic high-finesse optical enhancement cavity.
• Pumping the cavity with a narrow-band continuous-wave laser.
• Directly measuring the ratio of coherent to spontaneous Raman scattering signals in a gaseous medium.

Main Results:

• Achieved an enhancement ratio exceeding 10^9 for coherent Raman scattering signals over spontaneous Raman scattering.
• The measured enhancement ratio closely matched theoretical predictions.
• Demonstrated the method's effectiveness for trace gas detection.

Conclusions:

• The proposed method offers a significant advancement in ultrasensitive detection of trace gases.
• This technique is particularly promising for homonuclear diatomic molecules undetectable by absorption spectroscopy.
• The high enhancement factor validates the use of optical cavities in coherent Raman spectroscopy for trace analysis.