Light forces
This chapter introduces the interaction of motional degrees of freedom with light and internal atomic states. We begin by re-visiting the optical Bloch equations, and show how that formalism already includes the basis for inclusion of spatial coordinates in the equations of motion. In particular, we show that the steady state solutions of the optical Bloch equations lead to a nice picture of how atoms excited by an electromagnetic field can feel a friction force. This formalism provides a basis for an exploration of laser cooling, due to the balance of momentum absorbed from light and momentum released in random directions through spontaneous emission. We find that this "spontaneous light force" mechanism is responsible for three important modern laser cooling techniques, optical molasses, beam slowing, and magneto-optical traps. When a very strong light field is applied, the dynamics change, allowing the dipole force of a light beam to manipulate atoms (even single atoms!) through a potential due to the AC Stark shift, as is seen through the dressed atom picture.
- Light forces from steady-state solutions
- 2009 Class notes
- see API pp. 370 - 378
- Further reading on friction force in a standing wave (not covered in class)
- C. Cohen-Tannoudji, Les Houches 1990, pp. 34-35
- J.P. Gordon and A. Ashkin, PRA 21, 1606 (1980)
- Applications of the spontaneous light force (2009 Class notes)
- Optical Molasses
- Beam Slowing
- Magneto-Optical Traps
- References:
- Molasses, beam slowing and MOT:
- Nice summary on both dipole traps and radiation pressure traps
- W.D. Phillips, Laser cooling and trapping of neutral atoms, in Laser Manipulation of Atoms and Ions, edited by E. Arimondo, W.D. Phillips, and F. Strumia, Proceedings of the International School of Physics “Enrico Fermi”, Course CXVIII (North-Holland, Amsterdam, 1992) Download
- Original paper on optical molasses, Chu et al.
- Original paper on MOT, Raab et al.
- Original papers on optical Earnshaw theorem
- Dipole forces and the dressed atom picture
- see API Chapter VI – worth reading!
- Important paper: J. Dalibard and C. Cohen-Tannoudji, J. Opt. Soc. Am .B 2, 1707 (1985)
