Design and analysis of a laser micrometer for undulator gap measurement applications

• Designed a laser micrometer for undulator gap measurement.
• The beam spot size and the linear velocity of the beam spot are measured.
• We get a constant value of spot size at ±3 mm to the focal length of the F-theta lens.
• The measurements are obtained with an accuracy of 3–5 µm.
• Maximum error in the measurement of gap is 3.5% and for solid object is 13%.

In this paper we report the design of a laser micrometer for undulator gap measurement studies. In this scheme, the parallel light emerging from the rotating polygon mirror passes through an F-theta lens makes a vertical line on the image plane. When an object intercepts the line, the interrupted and the uninterrupted light is detected in a DSO through a detector. The beam spot size and the linear velocity of the beam spot on the scan line are the two important parameters of the laser micrometer. The beam spot size measurements show that it is constant along the scan line for a number of RPMs. It measures a constant value at ±3 mm to the effective focal length of the F-theta lens. The measurements are verified for two types of objects i.e. solid object and a circular hole and also for an electromagnet undulator. The electromagnet undulator is measured with an accuracy of 3–5 µm.