Cascaded Stimulated Raman Scattering Of D₂O And Ice-Ih

Deuteroxide has always been a hot topic among scientists in the fields of physics,chemistry,biology,etc,so the research on the properties and structure of deuteroxide was also indispensable in the field of scientific research.Raman spectroscopy was an effective means of analyzing microscopic changes in molecules.We can visually observe the specific peak positions of the material through the obtained Raman spectrum,and understand the intrinsic vibration mode of the material through its peak positions.In this paper,liquid and D₂O ice Ih are used as the research objects to study the structure of two different forms of D₂O,the threshold of cascade stimulated raman scattering（SRS）,pulse width and their four-wave mixing（FWM）processes by spontaneous Raman spectroscopy and stimulated Raman spectroscopy.The filament effect and the change of conversion efficiency at different energies are discussed,and the mutual transformation process of strong and weak vibrational modes at different temperatures is expounded.1.Stimulated Raman scattering（SRS）of deuteroxide was investigated using a pulsed Nd:YAG laser with 532 nm wavelength.After the pump laser passing through the first sample cell（C₁）,the output light included the transmitted pump beam and the stokes SRS lights,where the frequency difference between them self-matches the O-D symmetric and antisymmetric stretching vibration modes,realizing the effect of resonance enhancement on the SRS signal in the second sample cell（C₂）.The 1^st and the cascaded 2^nd-order stokes and their coherent anti-stokes raman spectroscopy（Coherent Anti-Stokes Raman Spectroscopy-CARS）of both two modes were observed;symmetric vibrations are weak vibrational modes,the antisymmetric vibrations was called a strong vibration mode.The 2^nd-order stokes SRS and its CARS were firstly observed at 14.79 m J of pump energy.The pure stokes SRS are always collinear with the pump beam along the axial direction;some ring-like stokes SRS and CARS,which originates from the FWM processes.The energy conversion efficiency can reach to 54%.2.The temperature-variable spontaneous Raman and stimulated Raman scattering properties of D₂O ice Ih were studied.D₂O ice Ih high-order SRS and CARS were obtained.As the temperature decreases,the O-D symmetric and antisymmetric stretching vibration modes intensities interconvert,and only cascaded SRS of O-D symmetric stretching vibration modes（weak vibration modes）was observed in D₂O ice Ih.At the same time,the self-termination behavior of liquid D₂O SRS was obtained,which was attributed to the self-defocusing effect of the beam caused by the photothermal effect;D₂O ice Ih has higher thermal conductivity,and the self-defocusing effect is not obvious,so there is no self-terminating behavior of SRS.