High-Accuracy Angle Generator for Angular Calibration

Characterization and metrology (measurement) of super polished x-ray mirrors are extremely critical for the next generation x-ray free electron laser light sources. Currently, DOE light source facilities such as Linac Coherent Light Source (LCLS) in the Stanford Linear Accelerator Center (SLAC) solely rely on foreign resources to do the characterization and measurement based on the technology developed more than 20 years ago, which not only limits the measurement accuracy but also incurs the long waiting time and high cost, and might be subject to the availability of the foreign sources. For the national interest it is highly desirable to develop the characterization and measurement capability within the US. In this SBIR program we propose a device that is capable of providing high accuracy angular information that can meet the accuracy of less than 50 nrad over a range of about 20 mrad given in the solicitation. The innovation of the proposal is based on the principle that the angular information is not presented in the position space as normally done by a conventional angular measurement process, but it is presented in the frequency space using a laser wavelength, which inherently possesses high accuracy by the nature of the laser wavelength. For example, the frequency of a laser emitting near 780 nm is 3.85 x 108 MHz, while a commercially available laser wavelength meter can detect a frequency change to near 20 MHz. The resolution is then less than 0.1 PPM. In the angular space (that is, the position space), 1 mrad is a measurable quantity using a high accuracy measuring device. The 50 nrad angular quantity is equivalent to 50 PPM change. From this simple comparison it is evident that the proposed innovation offers a better resolution.