Frank V. Kowalski

Laser phase and frequency stabilization using an optical resonator

We describe a new and highly effective optical frequency discriminator and laser stabilization system based on signals reflected from a stable Fabry-Perot reference interferometer. High sensitivity for detection of resonance information is achieved by optical heterodyne detection with sidebands produced by rf phase modulation. Physical, optical, and electronic aspects of this discriminator/laser frequency stabilization system are considered in detail. We show that a high-speed domain exists in which the system responds to the phase (rather than frequency) change of the laser; thus with suitable design the servo loop bandwidth is not limited by the cavity response time. We report diagnostic experiments in which a dye laser and gas laser were independently locked to one stable cavity. Because of the precautions employed, the observed sub-100 Hz beat line width shows that the lasers were this stable. Applications of this system of laser stabilization include precision laser spectroscopy and interferometric gravity-wave detectors.

Broadband continuous-wave laser

A cw ring dye laser is constructed in which the light is shifted in frequency before being fed back into the gain medium. The active medium is R6G dye pumped by an argon-ion laser. An acousto-optic modulator is used to shift the frequency of the light inside the cavity. A continuous distribution of energy in a 0.75-nm bandwidth is observed in the output beam. No Fabry–Perot frequency structure is observed.

Frequency stabilization of a 0633-µm He-Ne longitudinal Zeeman laser

A new method of stabilizing the output frequency of a He-Ne laser in a longitudinal magnetic field has been developed. With simple modifications to a standard He-Ne laser tube we obtain a frequency stability of <1 MHz (<10(-9)) for an averaging time of 1 sec and a long term (5 months) frequency reproducibility of ~ +/-1 MHz.

Optical pulse generation with a frequency shifted feedback laser

A pulsed ring dye laser is constructed in which the light is shifted in frequency before being fed back into the gain medium. The active medium is R6G dye pumped by a continuous wave argon‐ion laser. An acousto‐optic modulator is used to shift the frequency of the light inside the ‘‘cavity.’’ With this device, we have generated optical pulses with a 9.6 ps FWHM of the autocorrelation trace and measured periods as short as 0.9 ns.

Digital wavemeter of cw lasers

The ratio of an unknown laser wavelength to that of a standard is quickly determined by a two-beam interferometer with a corner-cube reflector moving on an air track. Standard and unknown wavelength beams travel identical paths in opposite directions, so refractive index corrections are minimized. Accuracy is about six parts in 10/sup 8/. Absolute measurements of some iodine hyperfine component wavelengths are reported.

An improved wavemeter for cw lasers

We report on a modified version of our previous moving mirror wavelength measuring interferometer. Its accuracy has been experimentally confirmed to one part in 108. The device is simple and seems ideally suited for cw lasers.

Frequency shifted feedback dye laser operating at a small shift frequency

Abstract Experimental results are presented for a frequency shifted feedback dye laser for small shift frequencies. The laser system supports many frequency components simultaneously even though the gain medium is homogeneously broadened. The laser spectrum consists of a chirped comb of frequency components which, for low pump powers, are separated by the cavity mode spacing. The formation of modes and the chirp is explained using the passive characteristics of the cavity.

Laser Polarization Spectroscopy

Polarization spectroscopy makes use of the polarization dependence of the nonlinear interaction between two laser beams in a gaseous medium. The laser-induced optical anisotropy is calculated using a rate equation approach, and the effect of this anisotropy on a polarized probe beam is derived. The method is useful for Doppler-free spectroscopy, for similification of molecular spectra, and for relaxation studies. A comparison with other Doppler-free saturation spectroscopy methods shows an advantage in signal-to-noise for polarization spectroscopy. Recent high resolution experiments with hydrogen, molecular sodium, and nitrogen dioxide are presented.

Output characterization of a frequency shifted feedback laser: theory and experiment

Frequency shifted feedback cavity (FSFC) lasers can generate continuous broadband radiation or periodic picosecond pulses. To better understand these two different regimes a passive FSFC is modeled and its output in the time and frequency domains is calculated. Calculations of the FSFC output indicate that peaks observed using a Fabry-Perot spectrum analyzer can only occur when the FSFC cavity length and intracavity frequency shift satisfy a resonance condition. Calculations also indicate that a radio frequency spectrum analysis of the intensity should show sharp peaks which are independent of the FSFC frequency shift. Additionally, pulses propagating in a FSFC are insensitive to frequency shift detunings, suggesting applications as a stable source of ultrashort laser pulses. Experimental evidence confirming these findings is reported. Results indicate that a FSFC does not support conventional laser modes. >

Pulse generation with an acousto‐optic frequency shifter in a passive cavity

A train of pulses is generated by coupling the cw output of a single frequency He‐Ne laser into a passive ring ‘‘cavity’’ which contains an acousto‐optic frequency shifter. Each cavity pass shifts the frequency of the wave by 80 MHz. This results in an intensity pattern which is an Airy function in time. For a single frequency input, the output pulse width is 2 ns with a repetition rate of 80 MHz. Data are also presented on the output of this device for multimode cw input.