Douglas L. Franzen

Ultraviolet laser action from Cu II in the 2500‐Å region

We have obtained cw laser action from Cu II at 2486, 2506, 2591, and 2599 A by exciting a neon discharge in a copper hollow cathode. We have observed 7‐mW cw output power just above threshold and the output appears to saturate at 210 mW under quasi‐cw operation. The four ultraviolet laser lines observed originate from the 3d95s (3D) term of Cu II. The quantum efficiency of the 2500‐A laser transitions approaches 25%. Each of the four Cu II laser transitions has been employed in the past by spectroscopists as a secondary wavelength standard in the ultraviolet.

Optical waveform measurement by optical sampling with a mode-locked laser diode

Optical pulses from a GaAlAs laser diode directly modulated at a frequency f0 (971 MHz) are mixed in a LiIO3 crystal with optical sampling pulses at a frequency of f0 − 10 Hz from a mode-locked GaAlAs laser diode. The optical signal obtained by sum-frequency mixing in the crystal is observed with a photomultiplier and an oscilloscope. The original pulse waveform is reproduced clearly with a temporal resolution equal to the mode-locked laser-diode pulse width and at a repetition frequency of 10 Hz. Similar results are obtained with InGaAsP laser diodes at a wavelength of 1.3 μm.

cw laser oscillation in Cu II

We have obtained cw laser oscillation on 23 transitions of Cu II in the blue‐green and near infrared by exciting either a He‐Ar, He‐Ne, or a He‐Xe discharge in a copper hollow cathode. The Cu II wavelengths range from 4506 to 7988 A. Output characteristics of the Cu II laser lines as functions of helium pressure; He:Ar, He:Ne, and He:Xe mixture ratios; and discharge current are presented. Single‐line output power, from the 7808‐A transition of Cu II, of 150 mW has been obtained.

Accurate Measurements of the Zero-Dispersion Wavelength in Optical Fibers

We have developed a frequency-domain phase shift system for measuring the zero-dispersion wavelength and the dispersion slope of single-mode optical fibers. A differential phase shift method and nonlinear four-wave mixing technique were also investigated. The frequency-domain phase shift method is used to produce Standard Reference Materials that have their zero-dispersion wavelengths characterized with an expanded uncertainty (k = 2) of ± 0.060 nm.

Determining the effective cutoff wavelength of single-mode fibers: An interlaboratory comparison

The National Bureau of Standards (NBS), in cooperation with the Electronic Industries Association, conducted an interlaboratory measurement comparison among six fiber manufacturers to determine the effective cutoff wavelength of single-mode fibers. Measurement techniques based on transmitted power were used to determine cutoff wavelength on four fibers designed for single-mode operation at 1300 nm. NBS also contributed results using a spectral near-field technique. One standard deviation measurement spreads for the various techniques range from 6 to 12 nm. With the appropriate data analysis, single bend attenuation and power step methods give the same results. Both techniques are easily implemented as extensions to the usual spectral attenuation measurement.

Mode-locked, long-cavity, erbium fiber lasers with subsequent soliton-like compression

Erbium fiber lasers are described that have cavity lengths of 20-5000 m and are mode-locked at the fundamental cavity frequency using an integrated-optic intensity modulator driven by a novel pulse generator. Resulting optical pulses at 1536 nm were recorded with a synchroscan streak camera and show durations of 10-80 ps with peak powers over 6 W. The shorter cavities yield nearly transform-limited pulses, which are narrowed by solitonlike compression to approximately 5 ps after propagation through an external 14 km fiber.<<ETX>>

Absolute reference calorimeter for measuring high power laser pulses

A calorimeter for making absolute energy measurements of high power laser pulses is described. The calorimeter, based on volume absorption in a solid, is calibrated electrically and requires no window or vacuum environment. An error analysis is included giving the systematic and random errors of the instrument for a laser measurement. Briefly, the following performance is typical of the 32-mm x 32-mm aperture calorimeter: range 0.4-15-J; random error +/-0.2% (one standard deviation); systematic error +/-2.3%; and an upper operational limit of 3 J/cm(2). Most of the volume absorber documentation is applicable for 1.06 microm; however, the calorimeter should be useful from the near ir through the visible. Absorbers for use with CO(2) lasers in the 9-11-microm range are also discussed.

cw gas breakdown in argon using 10.6‐μm laser radiation

A very intense gas breakdown spark has been extended to a continuous arc in argon using a focused cw CO2 laser. To achieve cw breakdown, the focal volume of a mirror focusing a high‐power CO2 laser was preionized by a single pulse from a CO2 TEA laser. The electron density created by the pulsed laser is sufficient to start the cw plasma. This letter reports accurate measurements of pulsed thresholds as well as preionized cw thresholds for breakdown in argon. Also, a study of the time development of the cw plasma is presented.

Continuous Laser-Sustained Plasmas

Continuous plasmas sustained by a focused high‐power CO2 laser are described. The power required for maintaining a cw plasma following preionization has been determined for Xe, Kr, and Ar, and attempted for Ne and He. Measurements indicate the noble gases with the lowest ionization potentials have the lowest sustaining thresholds. Radiative properties of some of the plasmas were studied with calorimetric techniques. Under certain conditions, more than half of the incident laser radiation can either be scattered or absorbed by the plasma. A major loss mechanism for the plasma is shown to be radiation in the visible and ultraviolet. Spectra of low‐pressure Xe plasmas indicate the presence of ultraviolet transitions with a high contrast over the continuum.

Determining the mode-field diameter of single-mode optical fiber: An interlaboratory comparison

The National Bureau of Standards, in cooperation with the Electronic Industries Association, conducted an interlaboratory measurement comparison among fiber manufacturers. Evaluated were transverse splice offset, near-field, far-field, and variable aperture far-field methods for determining mode-field diameter. Measurements were performed on five single-mode fibers at both 1300- and 1550-nm wavelengths. At 1300 nm, agreement was fairly good with the average one standard deviation being 0.15 μm for mode-field diameters in the 8-11 \mu m range. Distinct systematic differences among various techniques were observed at 1550 nm where mode distributions are not as Gaussian.