Jun Yoda

Towards an accurate frequency standard at 1.5 /spl mu/m based on the acetylene overtone band transition

We have made a frequency standard operating at the 1.5 /spl mu/m region using the saturated absorption of the v/sub 1/+v/sub 3/ band of /sup 13/C/sub 2/H/sub 2/. To enhance the moderate power from a laser diode and to saturate a very weak molecular overtone transition, we used a Fabry-Perot (FP) cavity and inside of it we put an acetylene cell. In order to obtain a longer life time for the cell, we designed a new scheme consisting of a cavity with a ULE (ultralow expansion) glass spacer and a baked and sealed-off cell with Brewster windows. We observed the saturated spectrum having a 1 MHz spectral linewidth. The signal obtained using the same cell ten months later had the same signal-to-noise ratio (SNR) and spectral linewidth. We made two versions of the frequency standard and observed a beat note between these two lasers from which we derived the frequency stability, in terms of the square root of the Allan variance /spl sigma/(/spl tau/)=2.4/spl times/10/sup -13/ at an integration time /spl tau/=1000 s.

Portable I/sub 2/-stabilized Nd:YAG laser for international comparisons

We have established a compact and transportable I/sub 2/-stabilized Nd:YAG laser for international comparisons of laser frequency. The root Allan variance of the portable laser has reached 3.9/spl times/10/sup -14/ when the integration time is longer than 200 s. The results of an international comparison between the National Research Laboratory of Metrology (NRLM), Tsukuba, Japan and the JILA (formerly the Joint Institute for Laboratory Astrophysics), Boulder, CO, USA show that the frequency difference of the portable laser NRLM-Y1 and the JILA laser JILA-W (f/sub NRLM-Y1/-f/sub JILA-W/) was -2.5 kHz, when the cold-finger temperatures of NRLM-Y1 and JILA-W were kept at -10/spl deg/C and -15/spl deg/C, respectively. The averaged frequency offset between two NRLM lasers (f/sub NRLM-Y1/-f/sub NRLM-Y2/) was -1.1 kHz. A frequency variation of about 1.2 kHz was found for the frequency offset between two NRLM lasers, after NRLM-Y1 was taken for a round trip to Sydney for a comparison organized by the National Measurement Laboratory, (NML), Australia.

Frequency comparison of /sup 127/I/sub 2/-stabilized Nd:YAG lasers

A first international comparison of I/sub 2/-stabilized Nd:YAG lasers has been made between the National Research Laboratory of Metrology (NRLM), Tsukuba, Japan, the Joint Institute for Laboratory Astrophysics JILA (formerly the Joint Institute for Laboratory Astrophysics), Boulder, CO, the National Institute of Standards and Technology (NIST), Boulder, and the University of Colorado, Boulder. The results of the comparison show that the square root Allan variance of the portable NRLM laser has reached 2/spl times/10/sup -14/ when the integration time is larger than 300 s. Matrix measurements were made for five hyperfine components from a/sub 6/ to a/sub 10/ of the R(56)32-0 line. The averaged frequency difference between the NRLM and JILA lasers for four measurements made on three separate days was -4996 Hz (NRLM-JILA, at 532 nm) with a standard deviation of 88 Hz.

Saturation spectroscopy of an acetylene molecule in the 1550 nm region using an erbium doped fiber amplifier

Abstract We have observed saturated absorption of the ν 1 + ν 3 band of 13 C 2 H 2 using an extended cavity laser diode and an erbium doped fiber amplifier. These narrow lines are very promising candidates for wavelength/frequency standards in the 1550 nm region (the optical communication band). We also discuss the possibility of making a working standard in this wavelength region using a Fabry-Perot cavity cell.

Generation of continuous-wave ultraviolet light by sum-frequency mixing of diode-laser and argon-ion-laser radiation in β-BaB2O4

More than 1 microW of tunable continuous-wave radiation at 369 nm has been generated by sum-frequency mixing of the radiation from a 1310-nm diode laser with the radiation from a 515-nm argon-ion laser in a beta-BaB(2)O(4) crystal. The phase-mismatching tolerance for nearly optimum focusing of input beams was found to be several times as large as that for no focusing or the calculated value. This effect was caused by relatively large double refraction of beta-BaB(2)O(4).

Anharmonic Oscillation of Ions Trapped in a RF Trap with Light Buffer Gas

The effect of a light buffer gas on the anharmonic oscillation of ions trapped in a rf trap is studied. The rf resonance absorption signals showed a change of the signal height and the hysteresis with the sweep direction of the dc voltage or the probing frequency due to the anharmonicity of the pseudopotential well of a rf trap. It was found that the signals changed drastically or even disappeared depending on the pressure of buffer gas, although almost the same number of ions were trapped. These effects indicate that the sensitivity of detection of the trapped ions can be improved by appropriately choosing the pressure of the buffer gas and the sweep direction. The trapped ions could be detected until 76 h 20 min and the storage time of 1.3×105 s was determined when these parameters were optimized.

Laser cooling of a natural isotope mixture of Yb/sup +/ stored in an RF trap

We demonstrate laser cooling of Yb/sup +/, produced by ionization of a natural isotope mixture, stored in an RF trap. One of the three major even isotopes was directly laser cooled and other isotopes were simultaneously trapped as a result of sympathetic cooling. It was possible to carry out laser cooling to the temperature at which the cloud-to-crystal phase transition occurs for /sup 174/Yb/sup +/, as observed in the case where enriched isotopes are used. We observed sudden drops of fluorescence owing to pumping to the /sup 2/F/sub 7/2/ state in the case of a small number of trapped Yb/sup +/ ions. >

Resonance of the Macromotion of Ions Trapped in a RF Trap by the Subharmonic Oscillation

Yb+ ions were trapped in an uncompensated rf trap with light buffer gas and then the storage time, as well as the total number of the trapped ions, was determined by the rf resonance method. When the ratio of the frequency of the trapping field to that of the macromotion of the trapped ions was an integer, the total number and the storage time were smaller and shorter, respectively, than those obtained when the ratio was a half-integer. A theoretical calculation shows that this effect, called the subharmonic oscillation, is caused by excitation of the macromotion of the trapped ions by the leaked trapping rf field, in the case in which the ion trap has an octupole besides a quadrupole potential.

Determination of the Total Number of Ions Confined in an RF Ion Trap

The total number of N2 ions confined in an rf ion trap was measured at various pressures of N2 gas. It was found that the total number of the trapped ions was independent of the pressure of N2 and was determined by the maximum potential depth of the ion trap.

Frequency reproducibility of I2-stabilized Nd:YAG lasers

We have established four I2-stabilized Nd:YAG lasers to verify the frequency reproducibility of the lasers. The observed square root Allan variance of the four lasers was between 1 to approximately 4 X 10-14 depending on the obtained signal-to-noise ratio of the spectra, when the integration time is larger than 300 s. The observed frequency reproducibility of each laser was ranged from 9.1 X 10-14 approximately 1.5 X 10-13 (corresponding to frequency uncertainties of +/- 51 approximately 87 Hz). Frequency reproducibility of a group of lasers (four NRLM lasers) has been evaluated to be 8.2 X 10-13 (corresponding to a frequency uncertainty of +/- 640 Hz). One of the four NRLM lasers is a compact I2- stabilized Nd:YAG laser which is suitable to be transported to other laboratories for international frequency comparisons. Using this portable laser, we have accomplished frequency comparisons of Nd:YAG lasers between several metrological institutes in different countries. The absolute optical frequencies of the NRLM lasers were determined with an uncertainty of about 1.5 kHz by the frequency comparison between the NRLM and the JILA (formerly the Joint Institute for Laboratory of Astrophysics), Boulder, CO.