Optical frequency comb generator with carrier envelope offset frequency detection
The present invention provides systems and methods for optical frequency comb generation with self-generated optical harmonics in mode-locked lasers for detecting the carrier envelope offset frequency. The mode-locked laser outputs an optical frequency comb and a harmonic output. The harmonic output provides an optical heterodyne resulting in a detectable beat note. A carrier envelope offset frequency detector detects the beat note and generates an optical frequency comb signal. The signal can be used to stabilize the optical frequency comb output.
1. An optical frequency comb generator system comprising, a femtosecond (fs) mode-locked laser oscillator simultaneously outputting:
a first frequency comb at a first central optical frequency, and
a least one second frequency comb at a second central optical frequency which is different from the first central frequency, wherein the first and one second frequency combs spectrally overlap one another in overlap spectral regions in which the first and second combs heterodyne beat against one another; and
a photodetector configured to detect a heterodyne signal generated by the heterodyne beating and corresponding to a carrier envelope offset frequency.
2. The system of claim 1 , wherein the fs oscillator is configured with a nonlinear laser medium simultaneously outputting the frequency combs at a fundamental central frequency and a plurality of higher harmonics of the fundamental central frequency respectively, the overlapped combs being the combs at the fundamental and second harmonic, or the second and third harmonics, or third and fourth harmonics.
3. The system of claim 2 , wherein the first and second central frequencies of respective first and one second frequency combs comprise respective fundamental frequency and second harmonic thereof.
4. The system of claim 2 , wherein the first and second central frequencies of respective one and second frequency combs comprise the second and third harmonics of the fundamental frequency.
5. The system of claim 1 further comprising at least one spectral broadening element operative to broaden the first and one second frequency combs, wherein the spectral broadening element is located between the fs oscillator and the carrier envelope offset frequency detector.
6. The system of claim 2 , wherein the mode-locked laser is configured with a resonator cavity tailored for increased output at one or more of the higher harmonics.
7. The system of claim 2 , further comprising at least one spectral filter configured to modify the spectral content of the heterodyne heating combs.
8. The system of claim 1 , wherein the carrier envelope offset frequency detector is configured to provide a signal used to control the carrier envelope offset frequency and thereby stabilize the optical frequency comb output.
9. The system as in claim 1 , wherein the mode-locked oscillator is a Kerr-lens mode-locked mid-JR fs oscillator that is configured with a TM:II-VI type material with high second and third order nonlinearity and a polycrystalline structure, wherein the oscillator provides three-wave mixing via a random quasi-phase matching process.
10. A method of providing an optical frequency comb comprising;
simultaneously outputting at least two overlapped optical frequency combs at respective first and second central frequencies, which are different from one another, from a mode-locked laser, wherein the first and second overlapped combs heterodyne beating against one another in overlapped spectral regions, thereby generating a heterodyne signal;
detecting the heterodyne signal; and
generating a signal corresponding to the carrier envelope offset frequency based on the detected heterodyne signal.
11. The method as in claim 10 , further comprising;
providing the carrier envelope offset frequency signal to a carrier envelope offset frequency control system to stabilize the carrier envelope offset frequency.
12. A method of detecting a carrier envelope offset frequency in a Kerr lens mode-locked mid-IR polycrystalline Cr:ZnS oscillator based laser system with a self-generating harmonic output, the method comprising;
simultaneously outputting multiple optical frequency combs at respective central frequencies, which are different from one another and include a fundamental frequency and multiple higher harmonics thereof, directly in the Cr:ZnS material, at least two combs overlapping one another in overlap spectral regions, wherein the overlapped combs produce a heterodyne signal; and
detecting the heterodyne signal, and generating a signal corresponding to carrier envelope offset frequency based on the detected heterodyne signal.