Linear Raman spectroscopy on aqueous aerosols: influence of nonlinear effects on detection limits
详细信息 查看全文
文摘
The influence of stimulated Raman scattering on the characterization of aqueous aerosols by linear Raman spectroscopy was studied experimentally. Raman scattering from a chain of microdroplets was excited by an argon ion laser. Holographic Raman filters, a spectrograph and a cryogenically cooled CCD detector were used to record the spectra. A procedure to estimate the detection limits of Raman instrumentation is presented. For the set-up used here, the detection limit for nitrogen in a gas mixture was 3 ppm. The detection limit for aqueous aerosol particles was limited to 100 mg m−3 by the occurrence of stimulated Raman scattering (SRS). The first measurement of SRS with continuous-wave excitation in water droplets is reported. The SRS thresholds for water droplets in the size range of 15-75 μm were 0.3 to 1 MW cm−2. For droplets, which consist of a 5 M NaNO3 solution, the threshold was 0.2 MW cm−2. Continuous-wave excited four-wave mixing in microdroplets of NaNO3 solution is reported.