Proposal of a frequency-synthesis chain between the microwave and optical frequencies of the Ca intercombination line at 657 nm using diode lasers

Optical frequency combs: Coherently uniting the electromagnetic spectrum

Optical frequency combs were introduced around 20 years ago as a laser technology that could synthesize and count the ultrafast rate of the oscillating cycles of light. Functioning in a manner analogous to a clockwork of gears, the frequency comb phase-coherently upconverts a radio frequency signal by a factor of [Formula: see text] to provide a vast array of evenly spaced optical frequencies, which is the comb for which the device is named. It also divides an optical frequency down to a radio frequency, or translates its phase to any other optical frequency across hundreds of terahertz of bandwidth. We review the historical backdrop against which this powerful tool for coherently uniting the electromagnetic spectrum developed. Advances in frequency comb functionality, physical implementation, and application are also described.

Frequency measuring system using mirror gap stabilized Fabry-Perot interferometer

The mirror gap of a Fabry-Perot interferometer was stabilized with two laser diodes; one locked to the line frequency 385,243,555.14445 MHz of the F=3<--1 in 5D(3/2)<--5S(1/2) (87Rb) and the other to the 385,284,566.3663 MHz of the F=4<--2 in 5D(5/2)<--5S(1/2) (87Rb) [Opt. Commun. 102 (1993) 432]. The length of the mirror gap was adjusted to generate the zero-cross points simultaneously at both of the two line positions. The fringe signals obtained from an interferometer thus stabilized can be used as frequency markers having accuracies of the order of 10(10) depending on the finesse of the interferometer used. Based on measurement using Cs D1 hyperfine lines reported by Udem et al. [Phys. Rev. Lett. 82 (1999) 3568], the uncertainty of markers in the region 50 THz apart from the reference lines is +/- 5 MHz.

Accurate measurement of large optical frequency differences with a mode-locked laser

We have used the comb of optical frequencies emitted by a mode-locked laser as a ruler to measure differences of as much as 20 THz between laser frequencies. This is to our knowledge the largest gap measured with a frequency comb, with high potential for further improvements. To check the accuracy of this approach we show that the modes are distributed uniformly in frequency space within the experimental limit of 3.0 parts in 10(17) . By comparison with an optical frequency comb generator we have verified that the mode separation equals the pulse repetition rate within the experimental limit of 6.0 parts in 10(16).

Optical frequency division by 3 of 532 nm in periodically poled lithium niobate with a double grating

Optical frequency division by 3 of 532 nm is demonstrated by back-to-back difference-frequency generation in a periodically poled lithium niobate crystal with a double grating. The first grating generates 1596-nm light from 532- and 798-nm inputs, and the second grating mixes the 798-nm input and the 1596-nm output from the first grating to produce a second 1596-nm output. The beat signal between the two 1596-nm outputs is detected and frequency stabilized to yield the 3:1 frequency ratio.

Proposed sum-and-difference method for optical-frequency measurement in the near infrared

We propose a method for the determination of optical frequencies in the near infrared that is based on the nonlinear generation of the optical sum and difference frequencies of two near-infrared lasers followed by the comparison of the sum and difference frequencies with standards in the visible and in the far infrared, respectively. We also address questions of practicability and discuss some examples open to the method.