Rotationally resolved coherent anti-Stokes Raman spectroscopy by using a tunable optical parametric oscillator

Area of Science:

• Spectroscopy
• Laser Physics
• Chemical Analysis

Background:

• Coherent anti-Stokes Raman spectroscopy (CARS) is a powerful technique for molecular analysis.
• Achieving rotationally resolved CARS measurements, particularly for atmospheric gases like nitrogen, requires precise control over the light source.
• Optical parametric oscillators (OPOs) offer tunable laser output, but their application in high-resolution CARS needs specific configurations.

Purpose of the Study:

• To develop and evaluate two distinct approaches for performing rotationally resolved CARS measurements of nitrogen in air.
• To utilize a beta-barium borate optical parametric oscillator (BBO OPO) as the tunable light source for these CARS measurements.
• To demonstrate the capability of these methods for detailed analysis of nitrogen molecules.

Main Methods:

• A beta-barium borate optical parametric oscillator (BBO OPO) was employed as the tunable laser source.
• Two CARS techniques were implemented: scanned CARS using a continuously tuned, narrow-band BBO OPO with injection-seeding, and single-shot multiplex CARS using a free-running BBO OPO.
• Rotationally resolved spectra of nitrogen in air were acquired using both methods.

Main Results:

• The scanned CARS technique successfully provided rotationally resolved spectra of nitrogen by precisely controlling the BBO OPO wavelength.
• The single-shot multiplex CARS technique enabled rapid acquisition of rotationally resolved nitrogen spectra.
• Both methods demonstrated the feasibility of using BBO OPOs for detailed CARS analysis of nitrogen.

Conclusions:

• The study successfully demonstrated two effective BBO OPO-based CARS techniques for rotationally resolved nitrogen measurements in air.
• The scanned and multiplex CARS approaches offer complementary capabilities for atmospheric nitrogen analysis.
• These BBO OPO-driven CARS methods provide valuable tools for high-resolution molecular spectroscopy.