FEMTOLENSING - BEYOND THE SEMICLASSICAL APPROXIMATION

Femtolensing is a gravitational lensing effect in which the magnificat ion is a function not only of the positions and sizes of the source an d lens, but also of the wavelength of light. Femtolensing is the only known effect of (10(-13)-10(-16) M(circle dot)) dark-matter objects an d may possibly be detectable in cosmological gamma-ray burst spectra. We present a new and efficient algorithm for femtolensing calculations in general potentials. The physical optics results presented here dif fer at low frequencies from the semiclassical approximation, in which the flux is attributed to a finite number of mutually coherent images. At higher frequencies, our results agree well with the semiclassical predictions. Applying our method to a point-mass lens with external sh ear, we find complex events that have structure at both large and smal l spectral resolution. In this way, we show that femtolensing may be o bservable for lenses up to 10(-11) M(circle dot), much larger than pre viously believed. Additionally, we discuss the possibility of a search for femtolensing of white dwarfs in the Large Magellanic Cloud at opt ical wavelengths.