Alan A. Madej

A laser frequency lock referenced to a single trapped ion

Abstract A frequency lock has been developed which frequency stabilizes a portion of the output from an ultrastable diode laser to the narrow 5s 2 S 1/2 –4d 2 D 5/2 transition at 445 THz (674 nm) of a single, trapped and laser cooled 88Sr+ ion. Digital processing is used to record quantum jump data and to servo the frequency applied to an acousto-optic modulator which is used to scan a portion of the laser output across two, symmetrically displaced Zeeman components. Stable locking has been obtained resulting in uncertainties in the ion transition referenced laser frequency of less than 150 Hz.

Precision frequency measurement of the /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition of Sr/sup +/ with a 674-nm diode laser locked to an ultrastable cavity

We have measured the frequency of the 5s /sup 2/S/sub 1/2/-4d /sup 2/D/sub 5/2/ clock transition of a single Sr ion confined in a Paul trap. A diode laser locked to an ultrastable Fabry-Perot (F-P) cavity was used to probe the transition with a resolution of 3.5 kHz. The absolute frequency was determined from heterodyne measurements referenced to an iodine stabilized HeNe laser and a CO/sub 2/ laser yielding a value for the S-D transition of (444 779 043 963/spl plusmn/30) kHz. This work could lead to the development of a new optical frequency standard at 674 nm.

Accurate absolute reference frequencies from 1511 to 1545 nm of the ν1+ν3 band of 12 C2H2 determined with laser frequency comb interval measurements

Absolute frequency measurements, with uncertainties as low as 2 kHz (1×10−11), are presented for the ν1+ν3 band of 12C2H2 at 1.5 μm (194-198 THz). The measurements were made using cavity-enhanced, diode-laser-based saturation spectroscopy. With one laser system stabilized to the P(16) line of 13C2H2 and a system stabilized to the line in 12C2H2 whose frequency was to be determined, a Cr:YAG laser-based frequency comb was employed to measure the frequency intervals. The systematic uncertainty is notably reduced relative to that of previous studies, and the region of measured lines has been extended. Improved molecular constants are obtained.

Absolute frequency measurement of a laser at 1556 nm locked to the 5S1/2-5D5/2 two-photon transition in 87Rb

Abstract The frequency of a diode laser system at 193 THz (1556 nm), which is frequency doubled and locked to a two-photon transition in rubidium at 385 THz (778 nm), has been measured with a Cs-based frequency chain and a single Sr + ion standard at 445 THz. The output frequency of the diode laser system was measured to be 192 642 283 183 700 ± 500 Hz. After applying corrections for systematic offsets in the rubidium spectrum, the frequency of the 87 Rb 5S 1/2 ( F g =2)−5D 5/2 ( F e =4) two-photon transition is found to be 385 284 566 370.4 ± 2 kHz.

Accurate absolute frequencies of the ν 1 +ν 3 band of 13 C 2 H 2 determined using an infrared mode-locked Cr:YAG laser frequency comb

Absolute frequency measurements, with up to 1×10−11 level accuracies, are presented for 60 lines of the P and R branches for the ν1+ν3 band of 13C2H2 at 1.5 μm (194 THz). The measurements were made using cavity-enhanced, diode-laser-based saturation spectroscopy. With one laser system stabilized to the P(16) line and a second laser system stabilized to the line whose frequency was to be determined, a Cr:YAG frequency comb was employed to accurately measure the tetrahertz level frequency intervals. The results are compared with recent work from other groups and indicate that these lines would form a basis for a high-quality atlas of reference frequencies for this region of the spectrum.

Single-Ion Optical Frequency Standards and Measurement of their Absolute Optical Frequency

This work examines the current status of research on optical frequency standards based upon single trapped ions. Methods for the containment and laser cooling of such single-ion samples are briefly discussed. Detection of ultra-narrow reference transitions via the observation of quantum jumps is outlined, together with the progress in the development of laser sources to provide cooling, detection and probing for such standards. A brief discussion on methods employed to date on stabilization to single-ion transition resonances is given, together with a summary of some of the principal sources for systematic shifts in such systems. Progress in the investigation of Ba + ,S r + ,C a + ,H g + ,Y b + ,a nd In + single-ion reference transitions is given. The work concludes with an overview of the progress in the measurement of single-ion referenced optical frequency relative to the Cs realization of the SI second and other reference standards.

Measurement of acetylene-d absorption lines with a self-referenced fiber laser frequency comb

This paper employed a self-referenced fiber laser frequency comb (FFC) to create a reference atlas of transitions of another acetylene isotope whose band covers the C-band telecom spectrum from 195 to 198 THz. Using the FFC together with a cavity-based diode laser-saturation-absorption spectrometer, this uncertainty is reduced to less than 2 kHz. It is concluded that the self-referenced fiber laser comb provides a very reliable and straightforward system by which large numbers of reference frequencies can be measured.

Absolute heterodyne frequency measurement of the 88 Sr + 455-THz S–D single ion transition

A system is described for the absolute frequency measurement of a laser source at 445 THz probing a narrow resonance of a trapped single ion of strontium. The 474-THz frequency from a laser referenced to an iodinestabilized helium-neon laser and a known 29-THz frequency from a saturation-stabilized carbon dioxide laser are mixed in an AgGaS(2) nonlinear crystal to synthesize the 445-THz radiation. A preliminary measurement of the (88)Sr(+) 5s(2)S(1/2)-4d(2)D(5/2) center frequency yielded a frequency of 444779044.14 +/- 0.39 MHz (1sigma).

Absolute frequency measurement of the HeNe/I2 standard at 633 nm

Abstract The absolute frequency of a HeNe laser locked to a hyperfine component in 127 I 2 is measured using a frequency standard based on a single, trapped and laser-cooled 88 Sr + ion. A CO 2 laser, whose frequency is measured with a Cs-based frequency chain, is used to span the frequency interval between the ion standard at 445 THz and the HeNe/I 2 laser at 474 THz. The frequency of the f component of the 11-5 R(127) transition of our HeNe/I 2 standard laser is found to be 473xa0612xa0353xa0600xa0180±720 Hz at the exact operating conditions specified for the realization of the recommended value of this radiation.

Studies of saturated absorption and measurements of optical frequency for lines in the ν 1 + ν 3 and ν 1 + 2ν 4 bands of ammonia at 1.5 μm

A cavity-enhanced absorption spectrometer was used to saturate several lines of ammonia in the 1510 nm – 1560 nm region. Analysis of power broadening of the saturated absorption feature for one of the ammonia lines yielded a dipole moment value comparable to that of the lines in the ν1+ν3 band in acetylene. Highly reproducible frequency measurements of four ammonia line centres were carried out using a frequency comb generated by a mode-locked Cr4+:YAG laser. These results demonstrate the possible application of ammonia saturated absorption lines for frequency metrology and calibration in a spectral region lacking strong absorbers. To our knowledge, this is the first frequency measurement of saturated absorption lines in ammonia at near infrared frequencies and the first reported observation of saturated absorption lines in the ν1+2ν4 band.