Electric Field-Induced Coherent Anti-Stokes Raman Scattering in the Visible Region from Water Molecules

Plasmas coexisting with water have attracted increasing attention due to their broad applications. Understanding such systems requires determining basic parameters, including the electric field strength.

Electric-field-induced coherent anti-Stokes Raman scattering (E-CARS) in visible region (E-CARSv) is a highly sensitive electric field measurement technique. Given the ubiquitous presence of water molecules in many systems, they represent a practical choice as a probe species. We studied the dependence of the E-CARSv signal intensity on electric field strength to investigate the feasibility of electric field measurements using water molecules as probes.

A static electric field up to 380 V/mm was applied between opposing electrodes in a water vapor cell at pressures ranging from 0.05 atm to 1 atm. Two nanosecond lasers (λ = 532 nm and 2735 nm) were collinearly focused at the center of the gap between electrodes and the induced E-CARSv signal was measured.

The signal intensity is proportional to the square of the electric field intensity, consistent with theoretical predictions and previous studies. This linearity was maintened regardless of molecular density. The minimum detectable electric field was determined to be 6 V/mm (at molecular density: 8.2×10²⁴ m⁻³), which is comparable to the reported detection limits of E-FISH and E-CARS in infrared region (5 V/mm). [1,2]

[1] B. M. Goldberg et al., Plasma Sources Sci. Technol. 31, 073001 (2022).[2] O. A. Evsin et al., Quantum Electron. 25, 278 (1995).