测量激光远场能量分布

Detector Array for Measuring Far-field Energy Density Distribution of

Repetitively Pulsed Laser

YANG Pengling a,b, FENG Guobin a, WANG Qunshu a, WANG Jingjin b, CHENG Jianping b

a Northwest Institute of Nuclear Technology, Xi’an, China, 710024

b Department of Engineering Physics, Tsinghua University, Beijing, China,100084

ABSTRACT

A system based on detector array is developed to measure the far-field temporal and spatial distribution and absolute pulse energy density of the laser beam. In this experiment, the duration of the laser pulse is about 15ns, the repetition rate is 400Hz, and the diameter of the far-field beam is about 60cm. The detector array is composed of 112 Si-PIN photodiode detectors and arranged to be a disk with spatial sample rate of 0.4cm-1. Charge sensitive amplifiers and baseline restoration circuits are used to collect photocurrent of the detectors, and current-input AD converters with integrator front-end are used to digitalize the multi channel signals. The far-field laser beam profile is reconstructed with the spatial sample data using special arithmetic of spatial interpolation. The system is capable for absolutely measuring far-field energy density distribution of repetitively pulsed laser, with response wavelength between 400nm and 1100nm, minimal detectable pulse duration of about 10ns, and energy density of 0.1-100µJ/cm2.

Keywords: Pulsed laser, Energy density distribution, Absolute pulse energy, Beam profile, Detector array, Charge sensitive amplifier, Analog-to-digital converter

1. INTRODUCTION

Beam quality and intensity are critical characters of high power laser system. Accurately measuring the far-field laser irradiance distribution is an effective way to diagnose laser beam quality and study the atmospheric transmission effects for a high power laser system[1],[2]. Traditionally, witness plates and CCD cameras are used to fulfill this measurement. These methods can only give a relative intensity distribution. Thermopile detectors based on batteries of thermocouples are frequently employed for pulse energy determination, especially for high-energy lasers. However, such detectors are not accurate for low energy levels and have no spatial resolution. Thermopiles are also inadequate to perform direct energy determination at repetition rates exceeding few pulses per second. Pyroelectric ceramics are another important class of energy detector based on the temperature increment produced by the absorption of the laser radiation. Pyroelectric ceramics are more sensible than thermopile detectors. They can reliably determine pulse energies as low as few tens µJ without amplification electronics. In addition, the pulse repetition frequencies allowed by pyroelectric ceramics are also higher than those permitted by thermopiles. At

International Symposium on Photoelectronic Detection and Imaging 2007: Laser, Ultraviolet, and Terahertz Technology, edited by Liwei Zhou, Proc. of SPIE Vol. 6622, 66220T, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.790808

Proc. of SPIE Vol. 6622 66220T-1