M. W. Williams

A Triple Reflection Polarizer for Use in the Vacuum Ultraviolet

The construction and evaluation of an efficient and convenient reflection type polarizer, using three gold mirrors, which is useful in the 500-5000-A wavelength region is described. The polarizer is evaluated both by direct measurement of its polarization and by calculation from the measured optical constants of gold. The variation in optical properties and hence polarization is investigated for gold mirrors prepared by different workers. With this instrument it is possible, over a wide wavelength region, to obtain 95% polarization with approximately 15% transmission of the polarized beam.

The optical properties of Kapton: Measurement and applications

The optical properties of Kapton type H polyimide film, obtained from reflectance measurements, are presented for photon energies from 0.5 to 70 eV. Equations for the energy‐loss function, with parameters fixed by the optical data, are employed to calculate mean free paths and stopping powers for low‐energy electrons (100 eV to 10 keV) in Kapton. The values obtained show good agreement with those predicted by recently proposed analytical formulae for electron mean free paths and stopping powers in solid organic insulators.

Optical Properties of Liquid Carbon Tetrachloride, n‐Hexane, and Cyclohexane in the Vacuum Ultraviolet

The optical properties of three organic solvents, carbon tetrachloride, n‐hexane, and cyclohexane are reported from 2.0 to 10.65 eV. Reflectance measurements using a closed cell and transmission measurements using samples as thin as 800 A were made to determine the optical constants, n and k. The optical absorption is interpreted in terms of molecular excitations of the nonbonding and σ electrons.

Collective electron effects in molecular liquids

Abstract A knowledge of the interactions of radiation with molecular liquids such as glycerol, water and benzene has direct biological application in terms of understanding radiation damage to living material. Not only the amount of energy but the modes of energy deposition can be extracted from the dielectric functions if these are known over a sufficiently wide energy range. The experimental techniques and methods of data analysis which yield the dielectric functions are reviewed. The conditions necessary for the existence of collective electron effects in molecular liquids are considered and the collective behavior associated with a single oscillator and with a collection of oscillators is compared with the behavior of a free-electron gas. Experimental spectra for some molecular liquids in the energy region from 0 to 26 eV are analyzed for the degree of collective behavior exhibited.

THE OPTICAL PROPERTIES OF ADENINE FROM 1.8 TO 80 eV

Experimental measurements of the optical reflectance of solid adenine films have been obtained for photon energies extending from 1.8 to 80 eV. From these data we have established the complex index of refraction, the complex dielectric function, and the energy‐loss function Im(‐l/). Structure in the dielectric functions are ascribed to * transitions at photon energies less than ~9 eV and to * transitions at higher energies. A broad peak in the energy‐loss function near 24 eV is associated with a collective resonance involving all the valence electrons. Sum rule calculations are used to demonstrate the overall consistency of the data.

Optical properties of crystalline MgF(2) from 115 nm to 400 nm.

The refractive index of MgF/sub 2/ is measured as a function of wavelength from 115 nm to 500 nm using a semicylindrical single crystal sample. (AIP)

Optical properties of some aromatic liquids in the vacuum ultraviolet

The optical properties of benzene, pyridine, quinoline, and 2‐ethylnaphthalene in the liquid state have been studied for photon energies from 2 to 10.6 eV. For each liquid the extinction coefficient k has been obtained from transmission measurements, and self‐consistent values of the refractive index n calculated over the experimental energy range by a Kramers‐Kronig analysis. The calculated absorption cross sections per liquid molecule have been compared with the corresponding absorption cross sections per vapor molecule, where the vapor data have been obtained from the literature. The absorption cross section spectra for liquid and vapor are very similar in the energy region studied, such that the observed absorption can be attributed to the same electronic excitations in both phases. In addition, evidence of collective excitations of electrons, not seen in the vapor state, is seen in all four liquids.

Slope method for determining extinction coefficients

A method is presented for obtaining the extinction coefficient, k, of an absorbing medium from critical-angle measurements. The maximum value of the slope of the reflectance vs angle of incidence curve is very sensitive to k and relatively insensitive to the refractive index, n, the polarization, P, and to surface imperfections. Theoretical curves are presented relating the magnitude of this maximum slope to k for constant values of n and P. In practice, the accuracy obtainable is limited by problems of normalization of the measured reflectance.

Optical and electronic properties of the electron beam resist poly(butene-1-sulfone)

The optical properties of thin films of poly(butene‐1‐sulfone), PBS, an electron beam resist, are presented for the range of photon energies from 2.5 to 39.0 eV. The density of these films is found to be (1.39 ± 0.02) g cm−3. A sum‐rule calculation is used to demonstrate the overall consistency of the data obtained. The optical data are used to calculate inelastic electron mean‐free paths in PBS as a function of incident electron energy from 100 to 10 000 eV.

Optical properties and electron-attenuation lengths from photoelectric-yield measurements*

The photoelectric yield of an infinitely thick medium is examined as a function of the polarization and angle of incidence of the incident light, the refractive index, n, and extinction coefficient, k, of the photoemitter, and the attenuation length, L, of the photoexcited electrons in the photoemitter. It is found that the photoelectric yield is a maximum at an angle very close to θc given by n = sinθc and that the magnitude of the yield at this angle, relative to that for normal incidence, is dependent on k and L. In practice, if we know the polarization of the incident light, a least-squares fit of the experimental photoelectric yield as a function of angle of incidence can be made to the theory using n, k, and L as the adjustable parameters. This method is most sensitive for the determination of optical constants when n is close to, but less than, unity and k and L are small. These are just the conditions generally found in the soft x-ray region where it is difficult to obtain accurate optical constants from reflectance measurements. It is suggested that, in the energy region where it is applicable, this method for obtaining optical constants may be easier and more accurate than reflectance methods. When the magnitude of the yield near θc is dependent on both k and L, this quantity may be used to determine L if k is measured independently.