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Abstract
Apparatus and methods for generating mid-IR frequency combs using intra-pulse DFG. A mode-locked pulse generation laser generates near-IR pulses which are amplified. The amplified pulses are spectrally broadened by a nonlinear element, for example a normal dispersion highly nonlinear fiber (ND-HNLF) to generate broadened pulses. The nonlinear spectral broadening element is a transparent dielectric material having a cubic nonlinear response. Broadened pulses are temporally compressed to generate short, high-power pulses which few-cycle conditioned pulses which are ready for the intrapulse DFG process. The DFG block generates a mid-IR comb by difference frequency generation. It might comprise an orientation patterned GaP (OP-GaP) crystal or a poled lithium niobate (PPLN) crystal.
patent description
We present a new approach to generating a coherent comb of infrared frequencies utilizing intra pulse difference frequency generation. The central claims of this invention are:
- A simple technique to generate few-cycle pulses derived from an amplified Er:fiber mode locked laser. This technique involves nonlinear spectral broadening in normal dispersion fiber, followed by compression in anomalous dispersion glass.
- A simple one-step approach to use these pulses to drive difference-frequency generation in a nonlinear optical crystal that possesses a chi-2 nonlinearity. The output of the nonlinear crystal is an extremely broad infrared spectrum.
- The infrared spectrum consists of a comb of optical frequencies which are pure harmonics of the repetition rate of the mode-locked laser, with no other offset frequency.
- Via the combination of difference frequency generation and cascaded chi-2 spectral broadening with the few cycle pulse, we can use this approach to directly measure the offset frequency of the original frequency comb.
Our invention provides a robust source of coherent light in the infrared, that is difficult to obtain otherwise. There is rapid growth and increasing interest in this region of the spectrum because it is extremely important for spectroscopy, materials science, microscopy, chemistry, trace gas sensing, health diagnostics, to name a few.