An optical time domain reflectometry method of sensing a parameter to be measured in a region of interest comprises launching optical radiation (4) at a probe wavelength into an-optical fibre (5, 6) and producing electrical output signals in response to optical radiation backscattered from the optical fibre (5, 6). In one aspect of the invention the optical fibre comprises first and second sections (5, 6), the second section (6) having a lower intensity threshold for the onset of non-linear effects than the first section (5) and being deployed in the region of interest. Optical radiation (4) at the probe wavelength is launched into the said first section (5) at an intensity lower than the non-linear effects intensity threshold of the first section (5) but higher than the non-linear effects intensity threshold of the second section (6), the attenuation characteristics of the said first section (5) being chosen so that the intensity of the optical radiation (4) at the probe wavelength reaching the second section (6) is below that of the non-linear effects intensity threshold of the said second section (6). In another aspect of the invention the optical fibre comprises first and second sections connected together by a remote amplifier, the gain of the amplifier being selected so as to compensate for attenuation losses in the probe wavelength in the first section.

Optical time-domain reflectometry

A flexible light guide especially useful for guiding high power laser beams The light guide in one form includes a light conducting fiber surrounded by a protective shielding with a liquid cladding in the area between the fiber and the shielding Both ends of the fiber have an end surface and a tapered area of decreasing circumference joining each end surface with the fiber, the fiber being smaller in diameter than either end surface and the length of the tapered area at one end of the tapered area at the other end The tapered areas of the fiber are each surrounded by tubes having an inner and an outer diameter The end of at least one tube is fused to one end of one tube to guarantee perfect suspension of the fiber The suspension reduces unwanted beam divergence caused by bending of the tapered area

Flexible light guide

Method and apparatus are provided for remote in-situ detection and/or monitoring of selected compounds in liquid or gaseous media using one of several methods of Raman spectroscopy. The resulting Raman signal is conducted through optical fibers for recording a Raman spectrum at a distance from the instrument.

Optical-fiber raman spectroscopy used for remote in-situ environmental analysis

A flexible light guide of plastic tubing is filled with a liquid which does not wet the plastic material, and preferably also is hygroscopic. The plastic material of the tube is preferably Teflon, FEP, PFA or PTFE; the liquid, for example, is an inorganic solution, especially ionic solutions and alcohols, particularly water-like polyvalent alcohols, so that light rich in ultraviolet (UV) radiation will be transmitted essentially through the solution and not deteriorate the tubing, the non-wetting characteristics providing for a sharp interface between the liquid and the tubing.

Flexible light guide, particularly for medical/dental use

A spectroscopic system for the analysis of small and very small quantities of substances makes use for the purposes of energy transfer of cone-shaped aperture changers (14, 15) which are arranged in the object zone (8) between the light source (L) and the sample (9) and, during absorption measurements, also between the sample (9) and the inlet slot (3) of a spectrometer (1). If the form used is a double cone, the aperture changers (14, 15) facilitate an oblique coupling in a capillary tube accepting the sample (9) which acts as a step-waveguide for the coupled radiation.

Spectroscopic systems for the analysis of small and very small quantities of substances

A long length of liquid-core optical fiber is employed as a Raman cell, wherein the fiber core contains the material whose Raman spectrum is to be analyzed. Spectral intensifications of from 102 to 103 times greater than that obtained by conventional means are realized, using very small sample volumes. Optimum fiber lengths are disclosed.

G Walrafen

Papers

Method utilizing an optical fiber raman cell