Howard P. Layer

Direct frequency measurement of the I 2 -stabilized He–Ne 473-THz (633-nm) laser

The absolute frequency of the 473-THz He-Ne laser (633 nm), stabilized on the g or i hyperfine component of the (127)I(2) 11-5 R(127) transition, was measured by comparing its frequency with a known frequency synthesized by summing the radiation from three lasers in a He-Ne plasma. The three lasers were (1) the 88-THz CH(4)-stabilized He-Ne laser (3.39 microm), (2) a 125-THz color-center laser (2.39 microm) with its frequency referenced to the R(II)(26) (13)C(18)O(2)laser, and (3) the 260-THz He-Ne laser (1.15 microm) referenced to an I(2)-stabilized dye laser at 520 THz (576 nm). The measured frequencies are 473 612 340.492 and 473 612 214.789 MHz for the g and i hyperfine components, respectively, with a total uncertainty of 1.6 parts in 10(10). The frequency of the i component adjusted to the operating conditions recommended by the Bureau International des Poids et Mesures is 473 612 214.830 +/- 0.074 MHz.

Frequency-Stabilized Single-Mode Cavity Ring-Down Apparatus for High-Resolution Absorption Spectroscopy

We present a cavity ring-down spectroscopy apparatus suitable for high-resolution absorption spectroscopy. The central feature of the spectrometer is a ring-down cavity whose comb of eigenfrequencies is actively stabilized with respect to a tuneable, frequency-stabilized reference laser. By using dichroic ring-down cavity mirrors that are designed to have relatively high losses and low losses at the respective wavelengths of the reference laser and probe laser, the cavity stabilization dynamics are decoupled from frequency jitter of the probe laser. We use the cavity eigenfrequencies as markers in spectral scans and achieve a frequency resolution of ≈1 MHz. Five rovibrational transitions in the (2,0,1) vibrational band of water vapor near 0.935 μm are probed with a continuous-wave external-cavity diode laser, and their line strengths are determined and compared to literature values. Collisional narrowing effects and pressure shifting are observed, illustrating the applicability of the method for quantitat...

Description, Performance, and Wavelengths of Iodine Stabilized Lasers

A description is given of lasers stabilized to components of the (129)I(2) spectrum in the region of the 633-nm laser lines for (3)He-(20)Ne and (3)He-(22)Ne. Relationships between operational characteristics such as power output, peak size, and peak width are shown, along with their relationships to some of the controllable parameters such as excitation level, iodine absorption, and iodine pressure. We found an iodine pressure broadening of about 13 MHz/Torr with a 2.6-MHz zero-pressure intercept. The frequency shift associated with iodine pressure is roughly 2 x 10(-9) nu/Torr to the red. Power broadening and power shifts are small, about a 10% increase in width and about 2 x 10(-11) nu variation in frequency for a fivefold to sixfold increase in power. These lasers exhibit a frequency stability for 10-sec sampling time of about 2 x 10(-12) nu and a resetability of about 1 x 10(-10) nu. The absolute vacuum wavelength for one iodine component has been measured against the (86)Kr standard-(3)He-(20)Ne:(129)I(2), kappa lambda = 632 991.2670 +/- 0.0009 pm. The wavelengths of several other iodine components have been determined by measuring the frequency difference between them and the (129)I(2), kappa component. Among these are (3)He-(20)Ne:(129)I(2), i lambda = 632 990.0742 +/- 0.0009 pm: and (3)He-(20)Ne:(127)I(2), i lambda = 632 991.3954 +/-0.0009 pm. These results were obtained using the Rowley-Hamon model for asymmetry in the krypton line and assume that the defined value for the standard is axssociated with the center of gravity of the line profile. The indicated uncertainties are statistical. No allowance has been included for imperfect realization of the krypton standard or for uncertainty in the asymmetry model.

Laser wavelength comparison by high resolution interferometry

High resolution interferometry has been used to determine the wavelength ratio between two molecularly stabilized He-Ne lasers, one locked to a methane absorption at 3.39 microm and the other locked to the k peak of (129)I(2) at 633 nm. An optical beat frequency technique gave fractional orders while a microwave sideband method yielded the integer parts. Conventional (third derivative) peak seeking servoes stabilized both laser and cavity lengths. Reproducibility of the electronic control system and optics was a few parts in 10(12), while systematic errors associated with curvature of the cavity mirrors limited the accuracy of the wavelength ratio measurement to 2 parts in 10(10). The measured wavelength ratio of the methane stabilized He-Ne laser at 3.39 microm [P(7) line, nu(3) band] to the (129)I(2) (k peak) stabilized He-Ne laser at 633 nm was 5.359 049 260 6 (0.000 2 ppm). This ratio agrees with that calculated from the (lower accuracy) results of earlier wavelength measurements made relative to the (86)Kr standard. Its higher accuracy thus permits a provisional extension of the frequency scale based on the cesium oscillator into the visible spectrum.

Circuit design for an electronic self-nulling ellipsometer

Abstract The importance of automating the ellipsometer has been recognized by researchers active in the field and considerable attention has been given to the development of a practical instrument. The present work was motivated by the belief that a more satisfactory automatic ellipsometer could be developed if the all-electronic approach suggested by Winterbottom was used. This approach has resulted in the design and construction of an instrument that is sensitive, stable, relatively inexpensive and which has a response time that is of the order of milliseconds. The electronic circuits will easily lend themselves to duplication by investigators interested in such a device and are of such a configuration that existing instruments need only minor modifications. An automatic gain stage circuit is included to maintain maximum sensitivity where spectral emission and sensitivity variations are encountered, as in continuous wavelength scanning ellipsometric measurements.

Scanning tunneling microscopy applied to optical surfaces

The technique of scanning tunneling microscopy has been applied to topographic mapping of two optical surfaces: a ruled grating replica and a diamond-turned gold mirror. We have demonstrated the ability of the scanning tunneling microscope to measure surface topography of a ruled-grating replica over an area of 2 microm x 2 microm. Furthermore, surface structure on a diamond-turned gold mirror was observed that could not be detected by any other type of surface-sensitive microscope. These measurements yield information necessary for gaining a complete understanding of the diamond-turning process.

Acoustooptic modulator intensity servo

A device has been constructed that combines optical isolation and amplitude noise reduction by the use of a servo controlled acoustooptic intensity modulator. The isolation can, in principle, be perfect while the noise reduction can be significant up to about 100 kHz and as large as 80 dB at low frequency. This performance is accomplished by applying negative feedback around an acoustooptic modulator, servoing the intensity of the Bragg diffracted beam to a constant value.

Evidence of tumbling multiplets in saturation absorption spectra of SiF_4

Some implications of tumbling quartets, triplets, and doublets seen in high-resolution spherical-top spectra are discussed. Some of the first observed cluster splittings are shown in SiF(4) spectra and compared with the predictions of the quantum theory of clusters. Further potentially interesting spectroscopic experiments are proposed.

National Physical Laboratory–National Bureau of Standards iodine-stabilized helium–neon laser intercomparison

The frequencies of two helium-neon lasers stabilized by intracavity saturated absorption of iodine ((127)I(2)) built at the National Bureau of Standards (NBS) and the National Physical Laboratory have been compared by beat-frequency measurement. The NBS laser exhibited a power-dependent frequency shift that was reproducible and significant in size (2 x 10(-10)) over the working range of the power output. The origin of the power shift has not been established, but several possible sources of the shift have been eliminated by our investigations. Specifically, the effect is not electronic in origin. No similar shift was observed in two lasers built at the National Physical Laboratory.

High‐resolution stepping motor drive

A digital sine–cosine stepping motor drive has been constructed which decreases the rotational step size by a factor of 31. This system improves the smoothness and resettability of the motor and retains the conventional slew speed and accuracy.