C. S. Edwards

Absolute frequency measurement of a 1.5-µm acetylene standard by use of a combined frequency chain and femtosecond comb

We have developed and characterized a pair of Doppler-free acetylene-stabilized diode laser frequency standards as optical communications references. The Allan deviation sigma/f of an individual system reaches a minimum of 4 x 10(-14) at a sampling time of 5000 s, and the long-term lock-point repeatability is found to be 0.4 kHz (one standard uncertainty), corresponding to a fractional uncertainty of 2 x 10(-12). Using a combination of a frequency chain and a self-referenced femtosecond comb, we have measured the frequency of line P(16) of the v1 + v3 overtone band of 13C2H2 to be 194,369,569,385.9 (3.0) kHz. The uncertainty of this number is limited solely by the reproducibility of the standards.

Observation of the 5s 2 S 1/2 −4d 2 D 5/2 transition in a single laser-cooledtrapped Sr + ion by using an all-solid-state system oflasers

The first application, to our knowledge, of an all-solid-state system of lasers to the study of a single cooled trapped Sr(+) ion is described. Quantum jumps have been observed by driving the 674-nm 5s(2)S(1/2)-4d(2)D(5/2) transition, and preliminary observations of the line shape are reported. An upper limit for the temperature of a single ion, derived from the 674-nm linewidth, was 200 mK. If non-Doppler sources of broadening such as unresolved Zeeman structure dominate, then the temperature limit would be even lower.

Frequency-stabilised diode lasers in the visible region using Doppler-free iodine spectra

Abstract Hyperfine components of the 7-4, R(39) transition of the B-X system of 127 I 2 at 637 nm have been used to frequency-stabilise a pair of extended-cavity diode lasers. The variation of component frequency with laser operating parameters has been investigated. A frequency stability slope (square root of Allan variance) of 9.3 × 10 −11 τ −1 2 and a long term reproducibility of 28 kHz (5.9 × 10 −11 , 1 σ ) have been measured by analysing the beat-note between these lasers locked to components a 4 and a 13 . In addition, the absolute frequency of component a 4 has been measured to an uncertainty of 0.10 MHz (corresponding to 2.2 × 10 −10 , 1 σ ) by interferometric comparison with an I 2 -stabilised HeNe laser. The frequency separations of all hyperfine components with respect to a 4 are reported.

A 633 nm iodine-stabilized diode-laser frequency standard

An extended-cavity diode laser has been stabilized to hyperfine components of the 6-3, P(33) transition of the B-X system of 127I2 at 633 nm, and its performance evaluated by comparison with an iodine-stabilized He-Ne laser. The Allan standard deviation follows a slope of 3.8 × 10-11 τ-1/2, reaching a minimum of 1.7 × 10-12 at 500 s, and the reproducibility of the diode laser locked to component b21 has been determined to be 7 kHz (standard uncertainty) corresponding to a fractional uncertainty of 1.5 × 10-11. In addition, the influence of modulation depth, iodine pressure and axial power density on laser frequency has been investigated. Complete hyperfine interval sets and absolute frequency determinations of component b21 are presented for modulation depths of 2 MHz and 6 MHz.

A tunable diode laser absorption spectrometer for moisture measurements in the low parts in 109 range

A tunable diode laser absorption spectrometer for trace moisture measurements at atmospheric pressure using a strong water vapour absorption at 1393 nm has been characterized and its performance enhanced. It has been evaluated by comparison with the NPL Low Frost-point Generator and the signal temperature dependences of the modulator, cell and detector module have been investigated by the implementation of active temperature control. In tests over the moisture range 15 parts in 109 by volume (ppbv) to 1 ppmv, the spectrometer displayed a short-term sensitivity of 1.6 ppbv for an averaging time of 50 s and a reproducibility of 12 ppbv over a period of three months.

High precision trace humidity measurements with a fibre-coupled diode laser absorption spectrometer at atmospheric pressure

Laser absorption spectroscopy offers the potential for fast and precise trace moisture detection in gases at atmospheric pressure with a small cross sensitivity towards other molecules. We report on the development and calibration of a fibre-coupled tunable diode laser absorption spectrometer operating in the 1 - 100 ppm humidity range. The spectrometer was tested at three European humidity standards laboratories. The performance of the spectrometer was characterized by monitoring constant water vapour concentrations over several hours, yielding a good long-term stability, reproducibility and accuracy. The standard deviations of the measured water vapour concentrations for values above 5 ppm were below ±2%. Comparisons of the instrument with chilled mirror hygrometers demonstrated its fast response time. The dependences of the signal upon the flow rate and temperature are discussed.

Development of an IR tunable diode laser absorption spectrometer for trace humidity measurements at atmospheric pressure

There is an increasing demand for the measurement of trace humidity in air at levels down to a few parts in 10/sup 9/ (ppb/sub v/) at atmospheric pressure. This summary describes the development by a European collaboration of a diode laser absorption spectrometer capable of measuring trace humidity with an uncertainty of 5 ppb. The diode laser was a distributed feedback device, tuned to the 3,0,3/spl larr/2,0,2 rotation transition in the /spl nu//sub 1/+/spl nu//sub 3/ vibrational band of water vapour at 1393 nm. Two-tone frequency modulation spectroscopy (TTFMS) was chosen as it combines the advantages of being the most sensitive technique and is relatively straightforward to implement. After a number of refinements to the optical layout, TTFMS features were obtained with no observable background interference effects.

Precision interferometric frequency measurement of the 674 nm /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition in a single cold Sr/sup +/ ion

The narrow linewidth 674 nm /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition in a cold Sr/sup +/ ion confined within an RF Paul trap has been probed using an optically narrowed 674 nm diode laser offset-locked to a second diode laser stabilized to a high-finesse ultra-low-expansion reference cavity. The transition frequency has been measured by means of interferometric comparison with an iodine-stabilized 633 nm He-Ne reference standard. A preliminary value for the /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition line center is 444 779 045 (9) MHz, limited by residual micromotion and low magnetic field Zeeman splitting. >

Laser-cooling effects in few-ion clouds of Yb+

We report some laser-cooling effects in a few172Yb+ ions held in a Paul trap. Pronounced cloud-to-crystal phase transitions have been observed as discontinuities in the Yb+ fluorescence spectrum of the 369 nm cooling transition. The first reported two-dimensional images of Yb+ clouds with evidence of crystal structure have been recorded using a photon-counting position-sensitive detector. An ion temperature of 100 mK has been estimated from the size of a single ion image. Step-wise cooling of a re-heated, few-ion Yb+ cloud was also observed.

Laser cooling and probing of a trapped strontium ion using all‐solid‐state lasers

A single strontium ion confined within an rf quadrupole trap has been laser‐cooled and probed using all‐solid‐state lasers. Quantum jumps from the cold ion have been observed by driving the 674 nm 2S1/2‐2D5/2 transition. The 2D5/2‐state lifetime has been measured to be 347±33 ms in good agreement with previous measurements. Preliminary 674 nm lineshapes, constructed from quantum jump data, are presented, and their variation with residual micromotion and magnetic field discussed.A single strontium ion confined within an rf quadrupole trap has been laser‐cooled and probed using all‐solid‐state lasers. Quantum jumps from the cold ion have been observed by driving the 674 nm 2S1/2‐2D5/2 transition. The 2D5/2‐state lifetime has been measured to be 347±33 ms in good agreement with previous measurements. Preliminary 674 nm lineshapes, constructed from quantum jump data, are presented, and their variation with residual micromotion and magnetic field discussed.