Kinetic Investigation of Collision Induced Excitation Transfer in Kr*(4p 5 5p 1 ) + Kr and Kr*(4p 5 5p 1 ) + He Mixtures Md. Humayun Kabir and Michael C. Heaven Department of Chemistry Emory University Atlanta, GA International Symposium on Molecular Spectroscopy 66 th Meeting: June , 2011

Motivation  The development of high-power lasers using diode pumped solid-state and fiber lasers are currently limited by material damage and heat dissipation problem.  Optically pumped alkali (Cs, Rb, and K) vapor lasers have recently been demonstrated with high output power and high efficiency. Krupke et al. Opt. Lett. 23 (2003)

Atomic Rare Gas Lasers are attractive: Excellent beam quality at high powers Potentially scaleable to high powers Possibility of operating in the IR range Concept of Optically Pumped Atomic Gas Lasers atomic gas Diode Pump, p  atom

Objectives and Goal  Detailed knowledge of collision-induced energy transfer kinetics of Kr + Kr and Kr + He: quantum state populations for laser modeling.  To obtain both accurate and comprehensive state-to-state collisional rate constants for the Kr + Kr and Kr + He collisional systems.  Our interest in using elements other than the alkali metals is to expand the range of pump and lasing wavelength.  Optical pumping scheme can be used to pump the rare gas atoms that are in the metastable electronic states. Siegman et al. J. Appl. Phys. 49 (1978)

Stepwise Electron-Photon Excitation-Scheme 3P13P1 3P03P0 3P23P2 1P11P1 4p 5 5s 4p 5 5p 3 D 3 (2p 9 ) 3 S 1 (2p 10 ) 1S01S0 e - impact excitation 1 S 0 (2p 1 ) Coll. transfer 3 D 2 (2p 8 ) 1 D 2 (2p 6 ) 3 D 1 (2p 7 ) E/eV Radiative decay Quenching to other multiplet  E = 13 cm -1

Experimental Experimental conditions: p(Kr) =0.5-1 Torr, p(He) = 2-20 Torr Discharge: V; R=1 k  ; current = mA Discharge Period: 350  s; laser fired within the discharge. pump R Nd:YAG LaserDye Laser HV Rg PMT Digital ‘Scope Monochromator Delay Generator Computer

Emission Spectra of Kr Plasma

Time Dependent Fluorescence Decay of 2p 6 level

Decay Rates vs Discharge Voltage Radiation Trapping: when a resonance photon emitted from an excited atom is absorbed and re-emitted from the other atoms cause a dramatic lengthening of the measured lifetimes of resonance transitions.

De-excitation of Metastable States Kr m + e -  Kr * (upper excited levels) + e - Kr m + Kr  Kr* + Kr Kr m + e -  Kr ** (1s 2, 1s 4 levels) + e - Kr m + e -  Kr + + 2e - Excitation by electron collision on upper excited levels Quenching by two-body collision: Penning Ionization: Quenching by electron collision to radiative levels Ionization by electron collision Kr m + Kr m  Kr + + Kr + e -

Total Collisional Deactivation Rate Constants

Comparison to Deactivation in other Rare Gases

Fluorescence Spectra following 2p 6 Excitation

Population Evolution following Excitation of 2p 6 level

State-to-State Rate Constants

S IMULATION Master Equation: models the evolution of individual level populations The rate equations for the collisional energy transfer process in the Kr(4p 5 5p) manifold Excitation of the initial state by the laser pulse Radiative decay loss

Comparison between expt. & calc. Spectra

Is Optically Pumped Laser Scheme Favorable? 3P13P1 3P03P0 3P23P2 1P11P1 4p 5 5s 3D33D3 3S13S1 3D23D E/eV  E = 13 cm -1 Pumped State Upper Laser Level Optical Pumping Lasing k( 3 S 1 ) = 6 x cm 3 s -1 (upper bound) k 10  9 = 5 x cm 3 s -1

Conclusion  Time-resolved LIF measurements were used to examine Kr(4p 5 5p) + Kr and Kr(4p 5 5p) + He collisional energy transfer within the Kr(4p 5 5p) manifold for the first time.  Largest total and state-to-state rate constants were observed for the for 2p 8 and 2p 9 levels.  For the Kr(4p 5 5p) + He collisional system the upper bound rate constant for lowest 2p 10 level is found to be 6 x cm 3 s -1.  Measured rate constants for the Kr(4p 5 5p) + Kr and Kr(4p 5 5p) + He collisions are found to be fairly similar except the lowest 2p 10 level.