attoPUBLICATIONS attoCATALOG-2017/18 | Page 200

PAGE 198 Glossary attoSENSORICS technical terms Fabry-Pérot Interferometer Our FPS and IDS Sensor Systems rely on a low-finesse fiber-based Fabry-Perot Interferometer. A great advantage of this technology over other displacement sensing techniques is their electronic-free sensor heads. The physical dimension of the sensor head is reduced to the millimeter range. This miniaturization makes the sensor ultra-compact and also compatible with extreme environments such as ultra high vacuum and low temperature. The fiber-based design allows flexible alignment, thus making multiaxis measurements and large distances of fiber length (even covering kilometer long distances) an easy task. Environmental Compensation Unit (ECU) The ECU provides a fully automated refractive index compensation for contactless interferometric measurements at ambient conditions. Variations in air pressure, temperature, and humidity are recorded and used to automatically compensate for changes in the refractive index. Focusing Sensor Head The focusing sensor heads D4/F17 (sensor head diameter of 4 mm with a focal length of 17 mm), M12/F40, and D12/F2.8 are suitable to measure on a wide range of target materials as well as target surface qualities with low, medium, or high surface reflectivity. For example, the focusing sensor heads make it possible to measure on a BK7 glass object with a reflectivity of only 4 %. The sensor head M15.5/F40 includes a flexure structure to adjust the beam path angle with ±1°. Working Distance Distance between the front side of the sensor head and the target where a continuous measurement is possible. Absolute Distance Distance between the end of the fiber, which is represented by the mechanical stop, and the target. Focal Length The focal length F is the distance between the front side of the sensor head and the focal point. Alignment Tolerance The angular alignment tolerance represents the target‘s tilt range in respect to the laser beam (α in the figure below). The laser beam might not be parallel to the central axis of the sensor head (β in the figure below). At retroreflectors, the center of roration is defined as the center of the retroreflector. α Sensor Head Collimating Sensor Head The sensor head M12/C7.6 (sensor head with a M12 metric thread and a beam diameter of 7.6 mm) is suited with a collimating optics type especially designed for the use with retroreflectors. It is optimized to measure over longer distances. ±2° target‘s tilt range β F working distance absolute distance