Kaoru Sasaki

Two-Photon Spectroscopy of the 6S–8S Transitions in Cesium using an Extended-Cavity Diode Laser

Two-photon spectroscopy of the 6S–8S transitions in cesium was conducted using an extended-cavity diode laser for the first time, to our knowledge. The signal-to-noise ratio of the signals obtained shows a potential use for the transitions as a secondary frequency standard at 822 nm.

103-km-Long Remote Measurements of End Standards Using Low-Coherence Optical-Fiber Tandem Interferometer in Experimental Room

The length information of end standards is transmitted through a 103-km-long optical fiber in the experimental room. The system uses a low-coherence tandem interferometer and a single-mode optical fiber in the wavelength range of 1500 nm. Interference fringes are generated when the optical path difference of the first interferometer compensates that of the second interferometer. The end standards of up to 50 mm in length have been calibrated remotely with a standard deviation of about 34 nm.

Laser interferometer for calibration of a line scale module with analog output

NMIJ line standard interferometer has been modified for measurement of a linear scale module with analog output. The interferometer was developed for line standard calibration. The light source is a stabilized He-Ne laser. Before the modification, a line standard can be calibrated with an uncertainty of about 0.2 micrometer for the total length of 500 mm (k=2). After the modification, a linear scale module can be calibrated as well as a line standard. A linear scale is set in a support on a moving carriage. The displacement of the moving carriage is measured by the interferometer with a sampling frequency of 30 kHz to 300 kHz while the electronic output of the linear scale module is sampled with the same timing. The analog output of the line scale module is used instead of digital output because it is important to assure the simultaneous sampling of the displacement and the scale output.

Rubidium-stabilized diode laser for high-precision interferometer

An Rb-stabilized diode laser has been developed for use in a high-precision interferometer. The light source is a commercially available external-cavity tunable diode laser. The laser frequency is stabilized to a Doppler-free absorption line of Rb by the third-harmonic technique. The laser emits an output beam with a high power (more than 7 mW) and fast frequency modulation (10 kHz). The relative optical frequency uncertainty of 4.3×10 –10 is achieved for a 0.01-s averaging time.

Compact I2-Stabilized Frequency-Doubled Nd:YAG Laser for Long Gauge Block Interferometer

A compact I2-stabilized frequency-doubled Nd:YAG laser has been developed for a long gauge block interferometer. The laser frequency stabilization is realized by the third-harmonic technique, where a fast frequency modulation (20 kHz) is applied to the piezoelectric transducer attached on the laser crystal. The relative uncertainty of the laser frequency has reached 3.6×10-12 for a 0.01-s averaging time. It is theoretically indicated that the phase error in the interferometric measurement due to the optical frequency modulation is sufficiently small to measure the long gauge block up to 1000 mm. Long gauge block measurement up to 1000 mm was successfully demonstrated with the developed I2-stabilized frequency-doubled Nd:YAG laser.

Remote Measurements of Practical Length Standards Using Optical Fiber Networks and Low-Coherence Interferometers

Practical length standards are remotely measured using a tandem low coherence interferometer through an optical fiber network for communication of about 20 km length between Tsukuba City and Tsuchiura City in Japan. The reference low-coherence interferometer is installed at the National Institute of Advanced Industrial Science and Technology (AIST) and the measurement interferometer with a gauge block of 100 mm nominal length is installed at a calibration laboratory in Tsuchiura City. The optical fibers work as a common path for the tandem interferometric system. Interference fringes are generated when the optical path difference between the reference and measurement interferometers is equal, and thus the gauge block is measured within a standard uncertainty of 46 nm remotely.

Remote Calibration of Length Standards Using 47-km-Long Optical Fiber Network

The information of practical length standards is transmitted through 47-km-long optical fiber network between Tsuchiura city and Kashiwa city in Japan. Interference fringes are generated when the optical path difference of a low-coherence interferometer in the Tsuchiura relay station compensates that in the Kashiwa station. End standards of 100 mm length in the Kashiwa station are calibrated remotely within a standard deviation of 118 nm with the reference standards in the Tsuchiura station.

Remote Measurement of Refractive Index of Air Using Tandem Interferometer over Long Optical Fiber

The refractive index of air is accurately measured using a vacuum cell and a tandem low-coherence interferometer with a communication optical fiber of 30 km length with standard uncertainties of 0.20 ppm for the phase refractive index and 0.29 ppm for the group refractive index. Experimental results are compared with the value calculated from the equation for the refractive index of air using data obtained from measurements of the surrounding air, with a standard uncertainty of 0.22 ppm, and the difference between the average values is within 0.1 ppm. This method is applicable to the in situ high-precision measurement of optical length.

Remote and in-situ calibration of linear scale by low-coherence tandem interferometer

Technique of transferring length-information between two distantly-located low-coherence-interferometers through a single-mode-optical-fiber for remote and in-situ calibration of linear scale is developed. Results of 200 nm-deviation and 100 nm-standard deviation for 50 mm-length is preliminary achieved.

Group refractive index dispersion measurement using low-coherence tandem interferometer

A technique for the group refractive index dispersion measurement of transparent materials using a low-coherence tandem interferometer without knowledge of the sample thickness is proposed. The experimental result of BK7 show an accuracy of 10-5.