Dingquan Liu

The determination of infrared optical constants of rare earth fluorides by classical Lorentz oscillator model

Rare earth fluoride (REF3 ,R E= La, Ce, Pr, Sm, Er, Yb, Y) films were deposited on Ge(1 1 1) and silicon wafers in order to determine optical constants from the near infrared up to the high frequency tail of the reststrahlen band. The FT-IR transmission spectrum and the reflection spectrum were used to examine the infrared optical properties of the fluorides. The optical constants of the films in the infrared spectrum from 2 to 20 µm were calculated using the classical Lorentz oscillator model by fitting the transmission spectrum. The reflective spectrum of the fluorides on silicon was used to demonstrate the absorption difference in this region. It is found that the extinction coefficients of rare earth fluorides films with P nma structure (REF3 ,R E= Y, Yb, Er) are larger than the other fluorides films with P ¯ 3c1 structure (REF3 ,R E= La, Ce, Pr, Sm) from 15 to 20 µm. (Some figures in this article are in colour only in the electronic version)

Non-polarizing broadband dichroic mirror

A non-polarizing broadband dichroic mirror with high reflectance from 400 to 600 nm and high transmittance from 650 to 1000 nm was designed with a simple structure. The newly designed mirror showed good tolerance for angle, thickness and refractive index errors. Then the dichroic mirror was fabricated by electron-beam evaporation with ion-beam-assisted deposition (IBAD). The experimental spectral performances showed a good agreement with the theoretical curves.

LOW FREQUENCY ACOUSTIC RESPONSE OF SURFACE CRACKS BY ATOM FORCE ACOUSTIC MICROSCOPY

Surface crack of CeF3 films generated by thermal stress were characterized by scanning electron microscopy and atom force acoustic microscopy (AFAM). Low frequency (8–18 kHz) acoustic response of films and cracks was measured by AFAM. The low frequency acoustic response is similar to what had been got at several MHz or even higher frequency. It was found that surface elastic properties of CeF3 films can be easily qualitatively measured by low frequency AFAM.

Compositional dependence of absorption edges in evaporated Pb1-xGeTe thin films as infrared short-wavelength cutoff filters

Semiconductors which exhibit a very rapid transition from opacity to transparency at the intrinsic edge are particularly useful in making excellent absorption filters. In this paper, we report the investigation on composition dependence of absorption edges in the evaporated Pb1-xGexTe thin films, which will be of a potentiality to fabricate a single-layer infrared short-wavelength cutoff filter by means of controlling the composition and processes. It is revealed that for thin films with an identical Te concentration, the absorption edges will shift towards short-wavelength with the increase of Ge concentration x in films; whereas, for those with a similar Ge concentration within a small range of deviation, the edges will also shift towards the short-wavelength with Te concentration approach to stoichiometry.ÿÿ

UNDERLAYER ROUGHNESS INFLUENCE ON THE PROPERTIES OF Ag THIN FILM

The effects of the roughness of ZnS underlayer on the microstructure, optical, and electrical properties of nanometer Ag thin film have been investigated in this paper. Nanometer Ag thin films in glass/ZnS/7.5 nm Ag/30 nm ZnS stacks have been deposited and analyzed. In the stacks, the underlayers of ZnS have been sputtered with various thicknesses to generate various surface roughnesses. The X-ray diffraction (XRD) has been used to study the crystal structure of Ag films. The surface topography and the roughness of ZnS underlayer have been analyzed by atomic force microscopy. The sheet resistant will become larger as the increasing of the roughness. The optical constants can be derived by fitting the transmission and reflectance spectrum. From optical constants comparison of Ag films, with the surface of the stack becoming rougher, it was found that the refractive index will increase but the extinction coefficient will decrease.

Control of polarization for a broadband dichroic filter at 45° incidence

A method for the control of polarization for a broadband dichroic filter was reported and some design examples were elaborated. This method could be applied over a wide range of wavelengths and a wide range of polarizations in the transmission region. A nonpolarizing broadband dichroic filter and a broadband dichroic filter with certain polarization were designed and fabricated by electron beam evaporation with ion beam assisted deposition. The experimental spectral performances showed good agreement with their theoretical curves. In addition, the application of the method was discussed.

Influence on optical and electrical properties of silver layer by adjoining Ta2O5 layers

Two kinds of structural film stacks, Ta2O5\Ag and Ta2O5\Ag\Ta2O5, were made for investigating the influence on the optical and electrical properties of ultra-thin Ag film by e adjoining Ta2O5 layers. Different samples were prepared by changing the deposition condition of Ta2O5 with different Argon pressure and sputter power. All samples have a uniform 6nm thickness of Ag layer controlled by deposition time. Optical and electrical measurements were carried out on samples and from the transmission and reflectance spectrum the optical constants can be derived. For Ta2O5\Ag film stacks, from measurement we found that the optical and electrical properties of 6nm Ag film strongly depend on the deposition condition of Ta2O5 layers. The sheet resistance is changed from 12Ω to 31Ω and reflectance is changed from 21% to 46% at 2500nm wavelength, which indicate the difference in Ag layer structure. But for the Ta2O5\Ag\Ta2O5 stacks, the changed deposition condition of the upper Ta2O5 layers just bring slightly shift of the optical and electrical property.

Design and fabrication of a non-polarizing broadband dichroic filter

A non-polarizing broadband dichroic filter with high reflectance from 400 to 600nm and high transmittance from 650 to 1000nm was designed with a simple structure and fabricated by electron-beam evaporation with ion-beam-assisted deposition (IBAD). Experimental spectral performances showed a good agreement with the theoretical curves. In addition, the designed dichroic filter can also show high transmission from 670 to 930nm with non-polarization over a wide range of incident angles.

Improving low-temperature performance of infrared thin-film interference filters utilizing temperature dependence of refractive index of Pb 1-x Ge x Te

Pb1-xGexTe is a pseudobinary alloy of IV-VI narrow-gap semiconductor PbTe and GeTe, of which maximum refractive index corresponds to the ferroelectric phase transition. Since the temperature coefficient of refractive index can be tunable from negative to positive by changing the Ge composition, it is possible to utilize the intrinsic property in the fabrication of infrared thin-film interference filters. A simple Fabry-Perot type narrow-bandpass filter was fabricated, in which Pb0.94Ge0.06Te was substituted for PbTe. It was found that the low-temperature stability of the filter is obviously improved: in the temperature range of 80-300 K, the shift of center wavelength with temperature is reduced from 0.48 nm.K-1 to 0.23 nm.K-1; furthermore, the peak transmittance of filter fabricated with Pb0.94Ge0.06Te is ~3% over that fabricated with PbTe.