Stephen F. Jacobs

Continuous Optically Pumped Cs Laser

A continuously operating 7.18-μ laser oscillator has been built using optically pumped cesium vapor as the amplifying medium. A power of 50 μw is coupled out of the confocal resonator by means of a 45° BaF2 pickoff window. The measured intensity distribution is in good agreement with that derived from the Boyd-Gordon expression for the lowest-order mode.

Retroreflective arrays as approximate phase conjugators

Arrays of corner reflectors behave similarly to nonlinear optical phase conjugators in correcting phase distortions in imaging systems. An experimental demonstration and a preliminary analysis of these properties are presented.

Dimensional Stability of Fused Silica, Invar, and Several Ultra-low Thermal Expansion Materials

We have measured length change vs time for several low thermal expansion materials maintained in evacuated environments at constant temperature (near 300 K). Materials were two types of fused silica, Cer-Vit, ULE, Zerodur, Invar, and super Invar. ΔL/L was measured over a period of 170 days to a precision of two to three parts in 109. In addition, we have measured time-dependent changes in optical contact interfaces and have placed an upper limit on drift of optical phase shift on reflection from multilayer dielectric coatings.

Ultraprecise thermal expansion measurements of seven low expansion materials

We summarize a large number of ultraprecise thermal expansion measurements made on seven different low expansivity materials. Expansion coefficients in the -150-300 degrees C temperature range are shown for Owens-Illinois Cer-Vit C-101, Corning ULE 7971 (titanium silicate) and fused silica 7940, Heraeus-Schott Zerodur low-expansion material and Homosil fused silica, Universal Cyclops Invar LR-35, and Simonds Saw and Steel Super Invar.

Experiments With Retrodirective Arrays

A summary of experiments is presented which show how retrodirective arrays have been used to approximate phase conjugation.

Expansion hysteresis upon thermal cycling of Zerodur

Thermal cycling of Zerodur reveals hysteresis effects near 250 and 450 K. Similar behavior is not observed in ULE or fused silica. Cer-vit was not examined.

Ultraprecise Measurement of Thermal Coefficients of Expansion

A novel method for determining thermal expansion coefficients has been devised. It is based on the dependence of Fabry-Perot resonances on the mirror separation. The expansion sample is formed into an etalon spacer, with highly reflecting endplates optically contacted to each end. The Fabry-Perot resonances are probed by variable radiofrequency sidebands derived from a frequency stabilized 633-nm He-Ne laser. A change in sample temperature DeltaT causes a change in interferometer length DeltaL, which shifts the resonance frequencies by Deltanu. Then alpha = (1/DeltaT)(DeltaL/L) = (1/DeltaT)(Deltanu/nu). alpha can be measured with precision limited ultimately by the stability of the stabilized laser (1:10(9) with presently available commercial lasers). alpha vs temperature has been measured for samples of Owens-Illinois Cer-Vit, Corning ULE silica, and Schott low expansion glass-ceramic.

Dimensional stability of fused silica, Invar, and several ultralow thermal expansion materials

A method is developed for testing the long-term dimensional stability of an iodine-stabilized He-Ne laser, using a technique whereby thermal expansion coefficients are measured by forming a Fabry-Perot etalon from the sample and monitoring the optical resonant frequencies with tunable sidebands impressed on a laser beam from a frequency-stabilized He-Ne laser. A change of 1 ppm over a 3-yr period on the part of fused silica dimensions and the differential thermal expansion of Invar LR-35 and Super Invar materials are noted. The method is of interest for the metrology of extremely stable structures such as telescopes and optical resonators.

Surface figure changes due to thermal cycling hysteresis

How does thermal cycling hysteresis affect surface figure in low expansivity mirror substrates? Zerodur, ULE, and Cer-Vit 20.3-cm (8-in.) diam mirrors and dilatometer samples were thermally cycled at 6 and 60 K/h with uniform and nonuniform heating. Figure distortions as large as lambda/10 were observed only with nonuniform heating of standard Zerodur, which was the only material exhibiting thermal hysteresis. A new experimental Zerodur appears to be free of this problem.

Optical heterodyne (coherent) detection

The optical heterodyne principle is described and its history traced. Early hopes for optical communication by this technique were frustrated by problems of wavefront degradation and laser frequency instability. However, fiber optics has recently revitalized this as an attractive possibility. In the interim, many other successful applications have been found that exploit different advantages of the heterodyne principle. Several examples are described. A number of simple optical heterodyne experiments utilizing a HeNe laser and electrical spectrum analyzer are presented. Details are furnished concerning experimental requirements and special considerations for optical heterodyne detection.