Sarah L. Gilbert

Annealing of Bragg gratings in hydrogen‐loaded optical fiber

We have conducted a detailed study of the thermal stability of Bragg gratings written in hydrogen‐loaded and unloaded germanium‐doped optical fiber. Interference of either continuous‐wave or pulsed ultraviolet light was used to induce the index modulation gratings. Some gratings were kept at room temperature and others were annealed at fixed temperatures for 10–20 h. For temperatures between room temperature and 350 °C, gratings in the hydrogen‐loaded fiber showed significantly greater decay than those in the unloaded counterpart. The ultraviolet‐induced index modulation in hydrogen‐loaded fiber was reduced by 40% after 10 h at 176 °C, whereas it was reduced by only 5% in unloaded fiber under the same conditions. The annealing behavior of gratings written using the pulsed source was identical to that of gratings written with the continuous‐wave source, and the thermal stability of gratings in hydrogen‐loaded fiber did not depend on the magnitude of the index modulation. We also observed that the annealing...

Inexpensive laser cooling and trapping experiment for undergraduate laboratories

We present detailed instructions for the construction and operation of an inexpensive apparatus for laser cooling and trapping of rubidium atoms. This apparatus allows one to use the light from low power diode lasers to produce a magneto‐optical trap in a low pressure vapor cell. We present a design which has reduced the cost to less than

Growth of Bragg gratings produced by continuous-wave ultraviolet light in optical fiber

3000 and does not require any machining or glassblowing skills in the construction. It has the additional virtues that the alignment of the trapping laser beams is very easy, and the rubidium pressure is conveniently and rapidly controlled. These features make the trap simple and reliable to operate, and the trapped atoms can be easily seen and studied. With a few milliwatts of laser power we are able to trap 4×107 atoms for 3.5 s in this apparatus. A step‐by‐step procedure is given for construction of the cell, setup of the optical system, and operation of the trap. A list of parts with prices and vendors is given in the Appendix.

Frequency stabilization of a tunable erbium-doped fiber laser

We have written Bragg gratings of as much as 94% reflectance in germanium-doped optical fiber by two-beam interference of 244-nm continuous-wave UV light. We measured grating reflectance as a function of exposure time for UV light intensities ranging from 1.5 to 47 W/cm2. The observed dependence of index modulation on time and intensity does not agree with the predictions of a model based on depletion of a defect population by one-photon absorption.

Optical probing of cold trapped atoms.

A single-frequency Er-doped fiber laser that is tunable from 1.52 to 1.58 ,microm has been constructed. The laser linewidth was determined to be less than 1.6 MHz FWHM by observing the spectrum of the beat between the fiber laser and a 1.523-microm He-Ne laser. The frequency of the fiber laser was locked to several absorption lines of acetylene near 1.53 microm. This research demonstrates the inherent stability of fiber lasers and their potential for use in a wavelength standard for optical communications.

Laser-frequency stabilization using mode interference from a reflecting reference interferometer

Transitions between excited states of laser-cooled and laser-trapped rubidium and cesium atoms are probed by use of fiber and diode lasers. High-resolution Doppler-free spectra are detected by observation of the absorption and fluorescence of light from the intermediate level of two-step cascade systems. The optical double-resonance spectra show Autler–Townes splitting in the weak probe limit and more complicated spectra for a strongly coupled three-level system.

Absolute frequency measurements with a stabilized near-infrared optical frequency comb from a Cr:forsterite laser

We present a new method for locking the frequency of a laser to a reference-interferometer cavity. For a nonmode-matched input beam, the light reflected off a cavity contains an interference between the wave fronts corresponding to the various cavity modes. A detector placed at the proper position on the interference pattern provides a signal proportional to the imaginary component of the reflected field. As a function of laser frequency, this signal is dispersion shaped and can be used as the error signal for electronic frequency stabilization.

Wavelength references for 1300-nm wavelength-division multiplexing

A Cr:forsterite laser-based frequency comb is stabilized simultaneously to two NIST frequency references. Several optical frequency reference frequencies are then measured from 1315 nm - 1620 nm, including methane lines near 1330 nm.

High Accuracy Spectroscopy of Stored Ions

We have conducted a study of potential wavelength calibration references for use as both moderate-accuracy transfer standards and high-accuracy National Institute of Standards and Technology (NIST) internal references in the 1280-1320-nm wavelength-division-multiplexing region. We found that most atomic and molecular absorption lines in this region are not ideal for use as wavelength references owing to factors such as weak absorption, complex spectra, or special requirements (for example, frequency-doubling or excitation with an additional light or discharge source). We have demonstrated one of the simpler schemes consisting of a tunable diode laser stabilized to a Doppler-broadened methane absorption line. By conducting a beat-note comparison of this reference to a calcium-based optical frequency standard, we measured the methane line center with an expanded uncertainty (2/spl sigma/) of /spl plusmn/2.3 MHz. This methane-stabilized laser now serves as a NIST internal reference.

Interleaved, sampled fiber Bragg gratings for use in hybrid wavelength references

Physical limitations to the achievement of accurate, high resolution spectroscopy on stored ions are briefly discussed. For experiments on ion clouds, a compromise between frequency stability and second order Doppler shift uncertainty must be made. Expected performance for specific examples using single ions and ion clouds is discussed.