Laser Cooling Molecules Joe Velasquez, III*, Peter L. Walstrom †, and Michael D. Di Rosa* * Chemistry Division, Physical Chemistry and Applied Spectroscopy † Accelerator Operations and Technology, AOT-ABS (LA-UR ) AOT

Non-Arrhenius Chemistry at Very Low T Inelastic collisions at ultra-cold temperatures may have enhanced rates!? 2  molecule and 2 S atom colliding at low temperature result in two possible total spin values: S = 1 and S = 0: CaH + Li → ?? < 1K CaH + Li LiH + Ca ↓↑ ↑↑ R.V. Krems, Cold Controlled Chemistry. PCCP. 10, (2008).

Stark Deceleration (10s of mK) Common Cooling Techniques for molecules Photoassociation Other techniques: Buffer gas cooling, spinning nozzle velocity Input Velocity Distribution Output Velocity Distribution Laser

Laser Cooling Molecules Directly Molecular structure necessarily means electronic transition-cycling is inefficient! To laser cool a molecule one would like: 1.Large oscillator strength for a given one-photon transition 2.A highly diagonal Franck-Condon band 3.A clean upper electronic state with no curve-crossings  00 X-state A-state  00  01  02  0n v'' v' n

Molecule 00, nm 01, nm BeH MgH CaH SrH BaH NH BH AlH AlF AlCl Candidate Molecules M. D. Di Rosa, Laser-cooling molecules Eur. Phys. J. D. 31, (2004).

Candidate Molecules for Laser Cooling

Combined Beams to Instrument 2.4 m Source Zeeman Slower Cooling lasers (on beam axis) 1.25 T Dipole Experimental Frequency Monitoring Dye 1Dye 2 Diode 1 Diode 2 AOM

Fiber-Coupled Pulsed Laser Ablation Source Evacuated chamber Launch fiber (Ø  m) Ø1 cm Nd:YAG 2  16 m Long Fiber ( Ø um) In-vacuum Fiber ( Ø 800 um) Aspherical Lens Target Vacuum feedthrough Throughput approaches 60 % Could be improved through better and fewer SMA-SMA connections f/2 positive lens

Observed Lithium-7 Subcooling in Xe Jet

Laser Cooling Scheme

Building Density: A Page from Accelerator Physics Paramagnetic particles may experience a force in a magnetic field, The trap must have a minimum, nonzero field for the stored state, The stored state must be intrinsically different than the injected state (Liouville’s Theorem) F = ± grad (  B ) We can achieve quantum-state specificity through Optical Pumping

Optical Pumping of Li-7 at High Fields

Early Accumulator Designs Linear Trap (Solenoid/Hexapoles) “Racetrack” histogram of v r from Monte-Carlo simulation x z y Linear Trap Radial Velocity Acceptance time, sec z -coordinate, m No Stable Orbits

The Cusp Solenoid z x y Trapping Volume Entry Cusp Solenoid Axis ( y ), m xy Contour Plot of | B | | B | in T x -coordinate, m y -coordinate (beam axis), m | B |, T State-Switching and Trapped Extents

histogram of v r from Monte-Carlo simulation Acceptance Range Cusp Solenoid Linear hexapole histogram of v axial from Monte-Carlo simulation Radial Velocity Acceptance of Cusp Solenoid Radial Velocity, cm/sec Axial Velocity Acceptance of Cusp Solenoid Axial Velocity, m/sec Counts

xy and yz Orbit Projections for Cusp Solenoid y -coordinate (beam axis), m

We wish to thank the Los Alamos LDRD program for funding.