Design and analysis of a new device for low-order wavefront aberrations measurement

For a high energy laser, thermally induced wavefront distortions include a large proportion of low-order aberrations with large peak-valley (PV) value. In this paper we design a Low-Order Wavefront Aberration Detector which can detect the large peak-valley value of low-order phase aberrations. Different from Shack - Hartmann Wavefront Sensor, this device includes one sepcial diaphragm, six sets of optical focusing system and six displacement detectors. The length of Low-Order Wavefront Aberration Detector can be controlled within 200mm. the minimum low-order aberration coefficient of LOWAD is less than 0.5λ which is determined by the inherent aberration distribution of optical focusing system. And we can choose reasonable position sensitve detector or four-quadrant photo-detector to detect relatiove displacement of each focal point, and thus the measurement sensitivity of LOWAD is less than 0.1 λ and the measurement capability is more than 80λ. The new wavefront measurement device can be used to direct measure low-order aberrations for laser beam with large transverse area and do not need beam contracting system, and the size and cost is greatly below Shack - Hartmann Wavefront Sensor.