Karolis Balskus

Mid-infrared 333 MHz frequency comb continuously tunable from 1.95 to 4.0 μm

Idler pulses from a 333-MHz femtosecond optical parametric oscillator were carrier-envelope-offset stabilized using a versatile locking technique which allowed the resulting comb to be tuned continuously over a range from 1.95 μm to 4.0 μm.

1-GHz harmonically pumped femtosecond optical parametric oscillator frequency comb

We present the first example of a femtosecond optical parametric oscillator frequency comb by using a 333-MHz Ti:sapphire laser to achieve a stabilized comb at 1-GHz mode spacing in the 1.1-1.6-μm wavelength band.

87Rb-stabilized 375-MHz Yb:fiber femtosecond frequency comb

We report a fully stabilized 1030-nm Yb-fiber frequency comb operating at a pulse repetition frequency of 375 MHz. The comb spacing was referenced to a Rb-stabilized microwave synthesizer and the comb offset was stabilized by generating a super-continuum containing a coherent component at 780.2 nm which was heterodyned with a (87)Rb-stabilized external cavity diode laser to produce a radio-frequency beat used to actuate the carrier-envelope offset frequency of the Yb-fiber laser. The two-sample frequency deviation of the locked comb was 235 kHz for an averaging time of 50 seconds, and the comb remained locked for over 60 minutes with a root mean squared deviation of 236 kHz.

Atomically referenced 1-GHz optical parametric oscillator frequency comb

The visible to mid-infrared coverage of femtosecond optical parametric oscillator (OPO) frequency combs makes them attractive resources for high-resolution spectroscopy and astrophotonic spectrograph calibration. Such applications require absolute traceability and wide comb-tooth spacing, attributes which until now have remained unavailable from any single OPO frequency comb. Here, we report a 1-GHz Ti:sapphire pumped OPO comb whose repetition and offset frequencies are referenced to Rb-stabilised microwave and laser oscillators respectively. This technique simultaneously achieves fully stabilized combs from both the Ti:sapphire laser and the OPO with sub-MHz comb-tooth linewidths, multi-hour locking stability and without the need for super-continuum generation.

Frequency comb metrology with an optical parametric oscillator

We report on the first demonstration of absolute frequency comb metrology with an optical parametric oscillator (OPO) frequency comb. The synchronously-pumped OPO operated in the 1.5-µm spectral region and was referenced to an H-maser atomic clock. Using different techniques, we thoroughly characterized the frequency noise power spectral density (PSD) of the repetition rate frep, of the carrier-envelope offset frequency fCEO, and of an optical comb line νN. The comb mode optical linewidth at 1557 nm was determined to be ~70 kHz for an observation time of 1 s from the measured frequency noise PSD, and was limited by the stability of the microwave frequency standard available for the stabilization of the comb repetition rate. We achieved a tight lock of the carrier envelope offset frequency with only ~300 mrad residual integrated phase noise, which makes its contribution to the optical linewidth negligible. The OPO comb was used to measure the absolute optical frequency of a near-infrared laser whose second-harmonic component was locked to the F = 2→3 transition of the 87Rb D2 line at 780 nm, leading to a measured transition frequency of νRb = 384,228,115,346 ± 16 kHz. We performed the same measurement with a commercial fiber-laser comb operating in the 1.5-µm region. Both the OPO comb and the commercial fiber comb achieved similar performance. The measurement accuracy was limited by interferometric noise in the fibered setup of the Rb-stabilized laser.

Frequency comb metrology with a near-infrared optical parametric oscillator

We show the first absolute optical frequency metrology demonstration performed with an OPO. The OPO frequency comb shows ∼300-mrad integrated CEO phase noise and ∼70-kHz optical linewidth at 1557-nm when fully-stabilized to a radio-frequency reference.

Carrier-envelope offset frequency stabilization in a femtosecond optical parametric oscillator without nonlinear interferometry

The carrier-envelope offset frequency of signal pulses in a femtosecond optical parametric oscillator was stabilized with a position-sensitive photodiode. The technique is easily implemented, requires no nonlinear interferometry and has a wide capture range.

Optical Frequency Combs Based on Femtosecond Optical Parametric Oscillators

The development of femtosecond frequency combs based on optical parametric oscillators (OPOs) in our group is summarized. Dual combs generated in a single OPO cavity have been showed applications in precise spectroscopy.

Carrier-envelope offset frequency stabilization in a femtosecond optical parametric oscillator without nonlinear interferometry.

The carrier-envelope offset frequency of signal pulses in a femtosecond optical parametric oscillator was stabilized with a position-sensitive photodiode. The technique is easily implemented, requires no nonlinear interferometry and has a wide capture range.

Observations of complex frequency comb structure in a harmonically-pumped femtosecond optical parametric oscillator

Various schemes allow femtosecond optical parametric oscillators to produce pulses at harmonics of their pump laser repetition frequency, each apparently offering the possibility of generating widely-spaced, tunable frequency combs. Using a 100-MHz Ti:sapphire pump laser, we have compared two alternative optical parametric oscillator architectures, both leading to 300-MHz pulses but one configured in a cavity three times shorter than the pump laser and the other in a cavity one-third longer. Heterodyne measurements between the pump and each of these two systems show that they possess different carrier-envelope offset characteristics, with implications on the coherence and stabilization of the resulting combs.