Using a Fiber Laser Frequency Comb for Precision Photoassociation Spectroscopy A.K. Mills, Yi-Fei Chen, Jie Jiang, K. Madison and David J. Jones Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada Femtosecond Laser Frequency Combs …an absolute frequency reference Abstract: We demonstrate the use of difference frequency generation to reference a CW Ti:sapphire laser to a fiber laser femtosecond frequency comb. We generate locking signals used to stabilize the CW laser with difference frequency generation and second harmonic generation, and we compare their performance. Difference frequency generation allows for an expanded range over which the CW laser can be tuned. This system will be used to perform high resolution photoassociation spectroscopy in our Rb2 and LiRb ultracold molecule system. Measurement of CW NIR Laser with an Infrared Fiber Laser Frequency Comb CW laser is stabilized to frequency comb (its frequency relative to comb is measured) Good SNR is required in heterodyne beat >25 dB (100 kHz RBW) Fiber comb & Ti:sapphire have no spectral overlap! Nonlinear frequency conversion must be used Heterodyne beat measurement is performed to measure the frequency of an unknown optical source, opt Self reference comb uses an octave of optical bandwidth to extract the offset frequency of the comb, fo using an f-2f interferometer fo frequency of mth mode: m = mfrep + fo Difference Frequency Generation (DFG) CW laser & fiber comb mix in nonlinear crystal DFG comb mixes with fiber comb in IR (near 1550 nm) Advantages DFG SNR scales linearly with CW laser power Second Harmonic Generation (SHG) Fiber comb is doubled in nonlinear crystal Single SHG comb element mixes with CW laser in NIR ( Disadvantages SHG SNR saturates at low CW laser power SNR limited by SHG power per comb element Our Motivation: Photoassociation (PA) Spectroscopy in a Dual Species MOT of Atomic Lithium and Rubidium PA spectroscopy requires widely tunable laser sources Spectroscopy requires precision frequency reference Frequency comb is a reference grid for photoassociation lasers Results with BBO: Tuning range (SNR >25 dB) SHG: 22 nm DFG: 33 nm (with max power) Multiple measurement branches can be added using splitters and Erbium doped fiber amplifiers (EDFA) We are currently investigating periodically poled lithium niobate (PPLN) in place of BBO Funding: We gratefully acknowledge support from the following sources Canadian Foundation for Innovation BC Knowledge Development Fund Natural Science and Engineering Research Council University of British Columbia