These beam probes can be used with liquid light guides and fiber bundles to produce a large diameter collimated beam size. For applications using a fiber bundle and requiring a collimated beam size of less than 13 mm, the 77644 or 77645 Fiber Bundle Collimated Beam Probe should be used. Flange sizes of 1.5- and 2-in. are offered. The following considerations should be made when choosing a collimating probe:

• Numerical Aperture of the liquid light guide/fiber bundle
• Transmission Range of the liquid light guide/fiber bundle
• Half Angle Divergence, θ/2 of the liquid light guide/fiber bundle
• Beam Size required – this is dependent on wavelength and the optical design of the collimating probe
• Typical Collimation Zone – range of distances from the surface of the lens over which beam size and intensity distribution will be most stable

These beam probes accept the standard 11-mm Oriel fiber termination and hold the light guide or bundle in place with a set screw.

Rod mount and flange mount options are available for these beam probes – please see Mounts for Beam Probes.

These beam probes are used to collimate the diverging output from an Oriel fiber bundle. A collimating beam probe should be chosen based on the core material of the fiber bundle being used (standard glass or fused silica). It should be noticed that a well collimated beam cannot be produced from a larger aperture fiber bundle. The smallest divergence angle possible for a perfect optical system is given by: θ = tan^-1(d / f), in which θ = full angle diverged, d = fiber bundle diameter and f = lens effective focal length.

The 77646 is a focusing beam probe for fused silica fiber bundles. A 19-mm focal length, f/1.7 fused silica collimating lens is included with the probe. The fiber bundle is placed one focal length from this lens to produce a collimated beam. The or other 0.5-inch diameter fused silica lens must be purchased separately and installed into the beam probe to create a focused image at a distance that is one focal length of the additional lens. The SPX012 has a focal length of 19 mm. Aside from lens diameter and material, the following should also be considered when choosing a secondary, focusing lens to add to the 77646:

• Lens Focal Length
• Working Distance – the distance from the outer edge of the beam probe to the point at which the output focuses, 7 mm less than the focal length of Lens 2
• Magnification – the ratio of the focal lengths of Lens 2 to Lens 1 (19 mm) Output Beam
• f/# -this parameter assumes the beam from the fiber bundle fills Lens 1

Note that working distance and magnification can be changed by moving the fiber bundle within the probe.