Abstract
We report the first Kerr-lens mode-locked (KLM) bulk frequency comb in the 1-μm spectral regime. The fundamental KLM Yb:CYA laser is pumped by a low-noise, high-bright 976-nm fiber laser and typically provides 250-mW output power and 57-fs pulse duration. Only 58-mW output pulses were launched into a 1.3-m photonic crystal fiber (PCF) for one octave-spanning supercontinuum generation. Using a simplified collinear f-2f interferometer, the free-running carrier-envelope offset (CEO) frequency was measured to be 42-dB signal-to-noise ratio (SNR) for a 100-kHz resolution and 9.6-kHz full width at half maximum (FWHM) under a 100-Hz resolution. A long-term CEO control at 23 MHz was ultimately realized by feeding the phase error signal to the pump power of the oscillator. The integrated phase noise (IPN) of the locked CEO was measured to be 316 mrad with an integrated range from 1 Hz to 10 MHz. The standard deviation and Allan deviation for more than 4-hour recording are 1.6 mHz and 5.6 × 10(-18) (for 1-s gate time), respectively. This is, to the best of our knowledge, the best stability achieved among the 1-μm solid-state frequency combs.
Highlights
Self-referenced optical frequency combs (OFC) from femtosecond mode-locked lasers have revolutionized the fields of precision measurements in frequency and time [1,2,3] since their birth at the end of 1990s [4]
The spectra of OFCs have extended to the extreme ultraviolet regime [5,6] and mid-infrared regime through different techniques [3,7]
Relevant researches reveal that Kerr-lens mode-locked (KLM) oscillators have intrinsically better potential for a very low carrier-envelope offset (CEO) noise compared to other kinds of mode-locked mechanism [26]
Summary
Self-referenced optical frequency combs (OFC) from femtosecond mode-locked lasers have revolutionized the fields of precision measurements in frequency and time [1,2,3] since their birth at the end of 1990s [4]. OFCs enable precision control over the electric field of the ultrashort laser, which makes it possible to generate attosecond pulses and achieve attosecond time-resolved measurement of the molecular dynamics process [9]. These increasing application requirements, on the other hand, stimulate the appearance of novel frequency combs based on different kinds of laser sources. For the 1-μm regime, though dozens of Yb-doped laser bulk oscillators were realized over the last decade years [29,30], most of them were limited by either low output power or long pulse duration to be developed towards frequency combs. The good performances of our novel frequency comb can be attributed to the low phase noise and high stability of the Yb:CYA oscillator and our improvement to the conventional two-arm f-2f interferometer, as will be described
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