Single Shot M2 Measurement for Near Infrared Laser Pulses in Real-Time

Summary form only give. High-power lasers are increasingly used in wide range of industrial manufacturing processes and scientific research [1,2]. Thermal lensing effects makes the high-power lasers not always stable over the very long periods of time required in manufacturing processes and thus changes the output laser beam parameters [3]. The key parameters for industrial lasers are M
²
value, focused spot size and its position shift with respect to the work-piece. Changes in these properties may cause the process to fail or yield low quality output. Real-time monitoring and instantaneous measurement of these parameters simultaneously throughout the manufacturing process is highly desirable. Such measurements also enables the laser developers to observe the variation of M
²
during cavity optimizations for achieving TEM
₀₀
mode. In this paper we present the novel cost-effective single shot technique capable of instantaneous measurement of laser M
²
, focus spot size and its position shift with respect to the work-piece in real-time. The measurement system consists of Er
³⁺
and Yb
³⁺
doped glass plate, focusing lens and the imaging system, without any moving parts as shown in the Fig. 1. Infrared laser beam is focused into the cross-sectional direction of photosensitive glass plate. The resulted visible up-conversion at 550 nm indicates the focusing property of the input laser beam. The visualized beam propagation in the glass is imaged precisely using a high-resolution optical system. Multiple second moment beam widths at different locations around the beam waist are measured simultaneously by processing the single image, which are used to determine M
²
and focus spot size accurately. This technique is fast and limited by the camera frame rates and allows the possibility of measuring in both continuous and pulsed operation with only a single laser pulse. The M
²
value and focus position shift measurements using this technique and comparison with commercial devices will be presented in detail during the upcoming congress.