Saturation in Multi-level Atoms from First Principles Dustin Stuart 1, Gar-Wing Truong 1, Tom Stace 2 Eric May 1, Andre Luiten 1 1 Frequency Standards and Metrology Group - University of Western Australia, 2 University of Queensland

Dustin Stuart - UWA People Involved Andre Luiten (UWA) Dustin Stuart (Honours Student) Eric May (UWA) Tom Stace (University of Queensland) Gar-Wing Truong (Ph.D Student)

Dustin Stuart - UWA Overview Quantitative Spectroscopy How weak does a laser beam need to be to avoid perturbing the atoms? We have developed a model that predicts the onset of saturation

Boltzmann Constant Doppler linewidth is related to temperature Carefully measure width to obtain Boltzmann constant

Experimental Setup

Dustin Stuart - UWA Hyperfine components of the Caesium D 1 line. Caesium D 1 Line Hz (exact)

Dustin Stuart - UWA Energy Levels: D 1 Line F = 3 F = 4 F' = 3 F' = 4 2 P 1/2 2 S 1/2 895 nm GHz GHz

Dustin Stuart - UWA Optical Pumping F = 3 F = 4 F' = 4 2 P 1/2 2 S 1/2

Dustin Stuart - UWA Optical Pumping |1  |2  |3  A 31 A 32 B 13 Laser-driven Excitation Spontaneous Decay

Dustin Stuart - UWA Optical Pumping |1  |2  |3  A 31 A 32 B 13 Spontaneous Decay Laser-driven Excitation

Dustin Stuart - UWA Optical Pumping |1  |2  |3  A 31 A 32 B 13 Spontaneous Decay Laser-driven Excitation

Dustin Stuart - UWA Relaxation Mechanism Collisions with the walls of the cell destroy the polarisation of the atoms Fresh atoms flow in from surrounding gas Pumped atoms eventually collide with a wall, causing relaxation Gaussian Laser Beam

Dustin Stuart - UWA Optical Pumping Population of laser- coupled ground state (v y = 170ms -1 ) Model Based On: Classical rate equations Effusive gas dynamics True Gaussian beam shape

Dustin Stuart - UWA Results

Dustin Stuart - UWA Different Components Theory Experiment ABCD

Dustin Stuart - UWA Zeeman Pumping |1  |2  |3  A 31 A 32 B 13 Laser-driven Excitation Spontaneous Decay

Dustin Stuart - UWA Optically Thick Samples At higher temperature, the atomic density is higher such that the vapour becomes optically thick and the saturation behaviour is different

Dustin Stuart - UWA Optically Thick Samples 1.Guess the form of u(r,z) (gaussian beam with exponential absorption) 2.Solve the rate equations to get atomic populations P i 3.Calculate absorption coefficient k from the populations P i 4.Calculate u(r,z) 5.Repeat until convergence...