1. 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