Abstract

A procedure by which simultaneous large- and small-scale inhomogeneities of the refractive index of an object can be assessed is presented. The information is obtained from a hologram and a simultaneous double-exposure holographic interferogram. The small-scale information is obtained by looking under magnification at the interference pattern which forms the actual hologram. This is complemented by observation of the image reconstructed from the same hologram. The large-scale information is obtained from the double-exposure holographic interferogram. The procedure was experimentally tested using a hand-drawn quartz fibre of ?100 ?m in diameter. A straightforward application is shown in which the object under study is a laser-produced spark in air. Early on, small-scale structures are present in this type of micro-plasma. The method can be directly applied to obtain the density profiles of hot-spots developed in a transient plasma discharge. Other possible applications are suggested.