Anti-Stokes Region

The anti-Stokes region of pararealgar from the Getchell, Mine:



The cause of the line at -275cm^-1 is unknown.

The laser line is seated more on the high side of the notch filter
and should be centered, but that would require considerable 
realignment of everything.

The cause of the difference in the peak offsets for positive and negative 
energy displacements is unknown. The wavelength calibration with Neon 
covered the shown range.


Raman Cooling

The following are simplistic statements and the actual physics 
is probably a bit more complex:

* The Stokes-scattered photons are less energetic (lower frequency) 
than the exciting laser's photons. They have transfered energy to
the specimen. 

* The anti-Stokes scattered photons are more energetic (higher frequency) 
than the exciting laser's photons. They are carrying away energy (heat) 
from the specimen. The energy gained by anti-Stokes photons 
came from molecular phonons. 
The phonons represent quantized energy from lattice mass oscillations.
Since molecular motion has lost energy to the laser's photons,
the molecular motion was lowered. Or equivalently, the molecule was cooled.
This is the basis for Raman Cooling.
Cooling molecules is trickier than cooling individual atoms.
This area of physics is advancing rapidly.

References: 
  Motional Quantum Ground State of a Levitated Nanoparticle from Room Temperature
  Military Raman Fiber Lasers