New 1.55 Micron Interferometer Announced

Precision-Optical Engineering has announced the availability of a new version of its INTERFIRE II infra red interferometers, operating at 1.55 microns.

This new instrument has been designed to meet the needs for testing the increasing numbers of optical systems operating at this wavelength. By utilising a CCD camera with NIR conversion optics, it has been possible to design a new interferometer using glass lenses and mirrors rather than the III-V material lenses and mirrors that are normally used in IR interferometers.

Optical systems designed for use in the near infrared at 1.55 microns are highly popular because the radiation at this wavelength is partially eye-safe. Applications include ranging systems, designation systems and scene illumination systems for surveillance. This wavelength is also used extensively in the communications industry.

The new instrument features a number of new components. A high resolution near infrared converter (Applied Scintillation Technologies, supplied in the UK by Laser Physics UK Ltd) is inserted between a large format lens and the camera, and converts the 1.495 - 1.595 micron wavelength band to wavelengths detectable using standard CCD cameras without fading or lag during use. Utilising standard CCD cameras brings major cost savings compared to specialised IR cameras.

A large format anti-reflection coated input window ensures maximum image resolution is transferred to the attached CCD camera. The camera system offers excellent signal-to-noise resulting in high sensitivity.

The better the signal to noise in the image, the better the quality of images of fringes that can be acquired. This in turn gives more accurate measurements.

The interferometer utilises two laser diode sources, one as a marker beam and one for the measurements. These are coupled into a fibre optic to give very precise alignment. Indeed because it is so precise, optical isolation must be provided using high quality polarisers and a 1/4 wave plate to prevent any reflections back into the fibre optic and ultimately the laser diode. The laser diodes supply plenty of power, but the sensitivity of the camera sufficient that they can be operated at relatively low power.

The new instrument has all the functional capabilities of the existing INTERFIRE Series, with a 35 mm aperture, zoom and focus systems and remote control. External beam expanders are also available for the instrument. The system is also fully compatible with phase shift measurement accessories. The high sensitivity ensures reliable fringe acquisition for this application and the absence of lag in the conversion optics means that there is no delay in the phase shift software performance.