Title: NIST Develops Advanced Optical Clock Technology Using Femtosecond Lasers
NIST researchers have developed a revolutionary optical clock technology using femtosecond lasers, which function as the “gears” of the clock. The femtosecond laser clockwork provides a phase-coherent link between optical frequencies and the microwave domain with unprecedented accuracy, down to 1 part in 10^19.
The key innovation is the self-referenced optical frequency comb, which allows counting optical cycles with femtosecond resolution using a compact and robust system. This breakthrough enables direct measurement of optical frequencies separated by hundreds of terahertz, connecting the optical and microwave domains.
The frequency comb is essentially an evenly-spaced array of optical modes in the output of a mode-locked femtosecond laser. The key technical points are:
1. The frequency of each mode can be described as n = Nfrep + fo, where N is a large integer, frep is the repetition rate of the laser, and fo is the carrier-envelope offset frequency.
2. Both frep and fo are typically microwave frequencies, providing the pathway to connect optical and microwave frequencies.
3. The frequency comb is stabilized to a laser referenced to an optical atomic transition, with frep providing the down-converted optical frequency.
NIST’s research focuses on building specialized femtosecond mode-locked lasers, developing nonlinear optical systems, and actively stabilizing the mode-locked laser to achieve the required accuracy levels.
Source: https://www.nist.gov/programs-projects/femtosecond-laser-frequency-combs-optical-clocks
Keywords: femtosecond, repetition, frequency, metrology, lasers
