CHANNELING OF VACUUM-ULTRAVIOLET RADIATION DOWN TAPERED CAPILLARIES AND PROSPECTS FOR A PHOTOEMISSION SPECTROMICROSCOPY

The transmission of linear tapered silica-glass capillaries is calcula ted both numerically and analytically for photon energies in the vacuu m-ultraviolet region (10-200 eV). The channeling factor C (ratio of tr ansmitted to line-of-sight flux) is given to a good approximation by 2 gamma/beta where beta is the taper angle and gamma is a characteristic decay angle determined entirely by the optical constants. The angular divergence (FWHM) of the output flux is 2.4 (betagamma)1/2, and the u seful length of the capillary is 2dgammabeta-3/2, where d is the diame ter of the exit aperture. Experimental measurements of photoemission s pectra on Au samples using tapered capillaries attached to the end of a conventional resonance lamp confirm these expectations. Channeling f actors greater than 10(3) should be achievable with submicron values o f d.