Steve C. Johnston

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.

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.

Some problems caused by birefringence in dielectric mirrors

Some problems caused by birefringence in dielectric mirrors are discussed with emphasis on the effects in laser cavities. Polarization sensitive applications are considered.

Spanning short cavity TEM00q frequency spacings by simultaneous excitation of many transverse modes

We report simultaneous excitation of at least 19 transverse modes of a curved‐plate, degenerate, Fabry–Perot resonator. The usefulness of spanning large free spectral ranges by means of transverse mode excitation is described.

Changes in surface figure due to thermal hysteresis

Thermal cycling hysteresis affects surface figure in low-expansivity mirror substrates. Zerodur, ULE, and Cer-Vit 8-in.-diameter mirrors and dilatometer samples were thermally cycled at uniform rates of 6 K/hr and 60 K/hr, and somewhat faster for nonuniform heating. Figure distortions as large as λ/10 were observed following nonuniform heating of standard Zerodur, which was the only material exhibiting thermal hysteresis. A new experimental Zerodur appears to be free of this problem.