Stable isotopic analysis of atmospheric methane by infrared spectroscopy by use of diode laser difference-frequency generation

An infrared absorption spectrometer has been constructed to measure the stable isotopic composition of atmospheric methane samples. The spectrometer employs periodically poled lithium niobate to generate 15 μW of tunable difference-frequency radiation from two near-infrared diode lasers that probe the ν3 rotational-vibrational band of methane at 3.4 μm. To enhance the signal, methane is extracted from 25 l of air by use of a cryogenic chromatographic column and is expanded into the multipass cell for analysis. A measurement precision of 12‰ is demonstrated for both δ13C and δD

Quenched narrow-line second- and third-stage laser cooling of 40Ca

We demonstrate three-dimensional (3-D) quenched narrow-line laser cooling and trapping of 40Ca. With 5 ms of cooling time we can transfer 28 % of the atoms from a magneto-optic trap based on the strong 423 nm cooling line to a trap based on the narrow 657 nm clock transition (that is quenched by an intercombination line at 552 nm), thereby reducing the atoms' temperature from 2 millikelvin to 10 microkelvin. This reduction in temperature should help reduce the overall systematic frequency uncertainty for our Ca optical frequency standard to < 1 Hz. Additional pulsed, quenched narrow-line third-stage cooling in 1-D yields sub-recoil temperatures as low as 300 nK, and makes possible the observation of high-contrast two-pulse Ramsey spectroscopic lineshapes.Comment: 21 Pages including figures. Submitted to JOSA

Stabilization of femtosecond laser frequency combs with subhertz residual linewidths

We demonstrate that femtosecond laser frequency combs (FLFCs) can have a subhertz linewidth across their entire emission spectra when they are phase locked to a reference laser with a similarly narrow line width. Correspondingly, the coherence time of the comb components relative to the reference laser can be of the order of a few seconds. Thus we are able to detect high-contrast spectral interferograms at up to 10-8 integration time between two FLFCs locked to a common optical reference

Femtosecond-Iaser-based synthesis of ultrastable microwave signals from optical frequency references

We use femtosecond laser frequency combs to convert optical frequency references to the microwave domain, where we demonstrate the synthesis of lO-GHz signals having a fractional frequency instability of ~ 3 . 5 X 10-15 at a 1-s averaging time, limited by the optical reference. The residual instability and phase noise of the femtosecond-laser-based frequency synthesizers are 6.5X 10-16 at 1 sand - 98 dBc/Hz at a I-Hz offset from the lO-GHz carrier, respectively. The timing jitter of the microwave signals is 3.3 fs

Design and Control of Femtosecond Lasers for Optical Clocks and the Synthesis of Low-Noise Optical and Microwave Signals

This paper describes recent advances in the design and control of femtosecond laser combs for their use in optical clocks and in the synthesis of low-noise microwave and optical signals. The authors present a compact and technically simple femtosecond laser that directly emits a broad continuum and shows that it can operate continuously on the timescale of days as the phase-coherent "clockwork" of an optical clock. They further demonstrate phase locking of an octave-spanning frequency comb to an optical frequency standard at the millihertz level. As verified through heterodyne measurements with an independent optical frequency standard, this provides a network of narrow optical modes with linewidths at the level of ~ 150 Hz, presently limited by measurement noise. Finally, they summarize their progress in using the femtosecond laser comb to transfer the stability and low phase-noise optical oscillators to the microwave domain

420-MHz Cr:forsterite femtosecond ring laser and continuum generation in the 1-2-my m range

We demonstrate a chromium-doped forsterite femtosecond ring laser that generates 30-fs pulses at a 420-MHz repetition rate with nearly 500 mW of average power. The compact solid-state design and broad spectral output make this laser attractive for telecommunications applications in the 1.3-1.5-μm region. Additional spectral broadening of the laser output in highly nonlinear optical fiber leads to octave-spanning spectra ranging from 1.06 to 2.17 μm. The octave is reached at a level of 18 dB below the peak. The underlying optical frequency comb can be linked to existing optical frequency standards

Absolute-frequency measurements with a stabilized near-infrared opticalfrequency comb from a Cr:forsterite laser

A frequency comb is generated with a chromium-doped forsterite femtosecond laser, spectrally broadened in a dispersion-shifted highly nonlinear fiber, and stabilized. The resultant evenly spaced comb of frequencies ranges from 1.1 to beyond 1.8,um. The frequency comb was referenced simultaneously to the National Institute of Standards and Technology's optical frequency standard based on neutral calcium and to a hydrogen maser that is calibrated by a cesium atomic fountain clock. With this comb we measured two frequency references in the telecommunications band: one half of the frequency of the d/{ crossover transition in 87Rb at 780 nm, and the methane 7)2 + 27)3 R(8) line at 1315 nm