It is hoped that this article will serve as a useful introduction to the art of stabilized lasers, especially for those who are joining this sport from other fields. It has become clear that pre- stabilization of the laser on the non-saturable resonance of a stable cavity is a good strategy: with adequate feedback system design, one can effectively replace the intrinsic noise of the laser with the measurement noise of the stabilizer system. By now sub-Hertz frequency control and optical phase locking have been demonstrated with most of these tunable sources. The ready access to modulation of the diode laser can lead to a very simple but impressive source, while the external stabilizer approach is attractive for dye and optically pumped solid-state sources. Current work on amplitude-stabilization of the laser pump may lead to reduction of the `intrinsic' solid state laser noise as well. With the current explosion of interest in atom trapping techniques we can look forward to major progress in the narrow-line laser/super- sharp absorber high resolution spectroscopy business. Applications range from atomic clocks to cold atom collision physics to tests of special relativity. The combination of ultra-stable lasers with cold atom interferometry will be especially powerful in offering new tests of atomic charge neutrality and of time reversal invariance via new limits on atomic electric dipole moments. Remarkably, a practical instrument for oil and gas prospecting might be based on a laser-diode/atom-interferometric measurement of local `g'.

The frequency stabilization of an AlGaAs laser using the linear optogalvanic signal from metallic vapor is reported. A hollow-cathode discharge tube, designed and built in our laboratory, has been used to obtain resonant optogalvanic lines corresponding to Ul and Thl transitions. These results show that the rich optogalvanic spectra of Ul and Thl can be efficiently used for the frequency-locking of semiconductor lasers.

The frequency stabilization of a semiconductor laser has usually been performed by applying a small modulation directly to the injection current. This paper reports a few frequency stabilization methods without a direct modulation, i.e., without a frequency broadening. These stabilization methods use the Faraday effect and/or the Zeeman effect of a saturated absorption line of the Rb atoms to obtain a control signal which is feedback to the injection current. These methods provide a better frequency stability and frequency control compared with the method using the direct modulation.

Optical feedback from velocity-selective magnetic-optical activity in alkali metal vapors has been shown to be an effective technique for simultaneously stabilizing the frequency and reducing the linewidth of Al_xGa_1-xAs/GaAs lasers. The ultimate frequency stability of such a laser is limited by the quality factor Q equals (nu) ₀/(Delta) (nu) of this frequency reference. In this letter we report the measurement of Q equals 6 (DOT) 10⁶ for optical feedback from velocity-selective magnetic-optical activity in Rb vapor.

We describe the design and performance of highly stable and high power Nd:YAG laser system for the interferometric gravitational wave detectors. The frequency of a diode-pumped Nd:YAG laser is stabilized by using a high finesse optical cavity, and its frequency noise is reduced to as low as 1.5 mHz/(root)Hz. Using a high power lamp-pumped ring Nd:YAG laser, single frequency output power of 4 W is obtained, and the injection locking is realized by using a diode-pumped laser as a master laser. We also show the design of high power single frequency diode-pumped Nd:YAG lasers.

Saturated absorption of iodine was observed using the polarization-stabilized internal-mirror He-Ne laser. An external ring resonator was used to enhanced saturated absorption. The P(33) line provided a sufficient signal to noise ratio for laser frequency stabilization.

One of the advantages of commercial ion lasers is their ability to produce high power cw output in a single longitudinal mode. When running in a single longitudinal mode, the short- term frequency 'jitter' (< 1 sec) is determined primarily by cavity vibration induced by water flow in the laser head. Using a piezo electric transducer to control the cavity length, we reduce the water-induced jitter by factors of up to 10.

The long- and short-term frequency stability of a diode laser is simultaneously improved by using an external cavity whose resonance frequency is locked to the center of a Doppler-free spectrum of the ⁸⁵Rb-D₂ line without laser frequency modulation. The obtained linewidth of the diode lasers is less than 100 kHz and the long-term stability in terms of the square root of the Allan variance (sigma) monotonously decreases from 2 X 10^-12 to 2 X 10^-14 as the averaging time (tau) increases from 100 ms to 100 s.

A strongly coupled external cavity semiconductor laser with stable frequency operation is reported in this paper. The typical linewidth, maximum tuning range and side-mode suppression ratio of the device are 100 kHz, 120 nm and 35 dB, respectively. The operation frequency is quite stable because of adopting strong external cavity feedback, temperature compensation cavity structure and double-stage temperature control. With the aid of active frequency control loop the frequency shift can be limited within several MHz over 24 hours. More than twenty tunable narrow-linewidth external-cavity semiconductor lasers have been developed in China.

We present a theoretical and experimental investigation of some of the instabilities encountered when a laser diode is exposed to optical feedback. The main emphasis in the paper is on the low-frequency instability seen for strong feedback levels.

This paper reports user requirements for frequency standards for optical communications and reviews physical possibilities for measurement standards to support those needs. A survey of the industrial and regulatory requirements for frequency standards for optical communications was made between October 1991 and January 1992. This was centered on the UK and Europe, but also took in responses from the USA and Japan. Over 70 representatives from 49 organizations were contacted, and a response exceeding 50% was achieved. The main requirement found was a need for two frequency standards per band in each of the 1.5 micrometers and 1.3 micrometers bands, with those in the 1.5 micrometers band needed first, and in the next 3 - 5 years. An accuracy of order 1 part in 10⁹ was desired for laboratory use, with an order of magnitude less for a transfer standard, and an order less again in the field. The physical possibilities for frequency standards in these bands are reviewed, addressing the use of atomic and molecular resonances.

This paper reports experimental work towards a laboratory standard based on the ²⁰Ne transition at 1.523 micrometers , some calibration measurements to 2.5 parts in 10⁷ on lines of C₂H₂ between 1.52 and 1.545 micrometers , and investigation of a standard at 1.56 micrometers involving a CO line. Progress is described towards measurement of the latter line by frequency doubling to, and beating against, a Rb D₂-line stabilized laser at 0.780 micrometers of known frequency.

We developed three types of frequency stabilized semiconductor lasers (LD) source or optical synthesizers using ¹²C₂H₂ or H¹³C¹⁴N absorption lines. This paper reports on the three methods below: (1) A frequency stabilized LD source controlled by sinusoidal LD current modulation reduced to lowest possible values. The maximum frequency deviation was +/- 5 MHz. And a frequency stability of 9 X 10^-10 (DOT) (tau) ^-1/2 (0.1 s 12C₂H₂ absorption line and a frequency stability of less than 1.0 X 10^-9 (10 s 13C¹⁴N absorption line were obtained from the beat method. (2) An optical synthesizer using two LDs and a newly developed frequency control method. The frequency synthesized range was +/- 2 GHz from the absorption frequency. A short-term frequency stability of about 2 X 10^-9 (DOT) (tau) ^-1/2 (0.1 s -10 (10 s