Peter Jungner

Delivering the same optical frequency at two places: accurate cancellation of phase noise introduced by an optical fiber or other time-varying path.

Although a single-mode optical fiber is a convenient and efficient interface/connecting medium, it introduces phase-noise modulation, which corrupts high-precision frequency-based applications by broadening the spectrum toward the kilohertz domain. We describe a simple double-pass fiber noise measurement and control system, which is demonstrated to provide millihertz accuracy of noise cancellation.

Hyperfine structure and absolute frequency of the 87Rb 5P_3/2 state

We have constructed two highly stable and reproducible (87)Rb D(2)-saturated-absorption spectrometers at 780 nm, using dither/third-harmonic lock-in detection and radio-frequency sideband techniques, respectively. We achieved +/-3-kHz reproducibility and agreement between these two independent systems. Heterodyne measurements of the hyperfine splittings of the 5P(3/2) state give its magnetic dipole (A) and electric quadrupole (B) hyperfine constants with a 10-fold reduction in uncertainty.

Absolute frequency of the molecular iodine transition R(56)32-0 near 532 nm

The absolute frequency of the hyperfine component a/sub 10/ in the transition R(56)32-0 of iodine has been measured using the D/sub 2/ line in Rb at 780 mm and an iodine-stabilized 633-nm He-Ne laser as references. This measurement provides a secondary frequency standard within the tuning range of a doubled Nd:YAG laser. The measured frequency of the a/sub 10/ component is 563 260 223.480 MHz /spl plusmn/70 kHz. >

Thermally induced self-locking of an optical cavity by overtone absorption in acetylene gas

Strong self-locking phenomena are observed when laser power is converted into heat by a weakly absorbing medium within a high-finesse cavity. Deposited heat leads to increased temperature and, for the case of weakly absorbing intracavity gases studied here, to an associated reduction of density and refractive index. This thermal change in refractive index provides self-acting cavity tuning near resonant conditions. In the experiments reported here a Fabry‐Perot cavity of finesse 274 was filled with acetylene gas and illuminated with a titanium:sapphire laser tuned to the P(11) line of the n1 1 3n3 overtone band near 790 nm. The dependencies of maximum frequency-locking range on gas pressure, laser power, and laser frequency sweep rate and direction were measured and could be well unified by analysis based on the thermal model. In the domain of strong self-tuning an interesting self-sustained oscillation was observed, with its several sharp frequencies directly and quantitatively linked to the acoustic boundary conditions in our cylindrical cell geometry. The differences between the behavior of acetylene near 790 nm and molecular oxygen with electronic transition near 763 nm are instructive; whereas the absorbed powers were similar, they differed strongly in their rates for internal to translational energy conversion by collisional relaxation.

Stability and absolute frequency of molecular iodine transitions near 532 nm

A frequency-doubled Nd:YAG laser has been stabilized to hyperfine transitions in molecular iodine near 532 nm via modulation transfer spectroscopy. This technique, together with the low noise of the source, yields excellent SNR (500 in a d kHz bandwidth); thus, an impressive frequency stability is achieved. The nearly systematic-free resonance signals obtained by modulation transfer spectroscopy give a correspondingly encouraging reproducibility, estimated to be about +/- 300 Hz. With two such stabilized lasers were found a pressure shift of only -1.3 kHz/Pa over the range 0.4-4.0 Pa and a power-dependent frequency shift of 2.1 kHz/mW. We have also measured the absolute frequency of the component a10 in the transition R(56)32-0 using the D2 line in Rb at 780 nm and an iodine-stabilized 633 nm He-Ne laser as references. The measured frequency is 563 260 223.471 MHz +/- 40 kHz. In turn, the absolute frequency of the D2 line was measured via the frequency difference between the D2 line and the two-photon transition 5S1/2 - 5D5/2 at 778 nm in Rb. Thus we now have realized a pure frequency measurement of this interval and of the 532 nm frequency.

Accurate cancellation (to milliHertz levels) of optical phase noise due to vibration or insertion phase in fiber-transmitted light

A single-mode optical fiber is a convenient and efficient transmission medium for optical signal. However, the optical insertion phase written on the light field by the fiber is very sensitive to the surrounding environment, such as temperature or acoustic pressure. This phase-noise modulation tends to corrupt the original delta-looking Hz-level optical spectrum by broadening it toward the kilohertz domain. Here we describe a simple and effective technique for accurate cancellation of such induced phase noise, thus allowing fiber-based optical signal transmission in very demanding high-precision frequency-based applications where optical phase noise is critical the system is based on double-pass heterodyne measurement and digital phase division by two to obtain the correction signal for the phase compensating AOM. The underlying physical principle is the fact that an optical fiber path ordinarily possesses an excellent degree of linearity and reciprocity, such that two counterpropagating signals can experience the sam phase perturbations. Overall, the fibers kilohertz level of broadening is reduced to sub-millihertz domain by our correction.

Measurement of the absolute frequency of molecular iodine transitions near 532 nm

The optical frequencies of several transitions in iodine have been measured using the D2 line in Rb 780 nm and an iodine-stabilized 633 nm He-Ne laser. This measurement provides a useful, stable and highly reproducible optical frequency reference in the green.<<ETX>>