Investigation On A Laser Beam Intensity Stabilization System

Fluctuations in environmental factors or power supplies(such as voltage or current sources)can significantly affect the intensity stabilization of laser output.Since these changes cannot be accurately predicted or even avoided in most cases,they tend to induce some noises into the intensity of the laser beam,which constantly affects the measurement sensitivity while using such lasers,making the development of a laser stabilization system very necessary.This thesis designs,constructed and discusses a simple,accurate,and cost-effective laser stabilization system.It uses a closed-loop feedback proportional-integral-derivative(PID)controller and the controlling method to determine the laser beam intensity,which is then stabilized.The system utilizes a low-noise and sensitive photodiode(PD)to detect and measure the intensity of the laser beam,and the output of the PD is used as the input of the PID controller implemented on an STM32F103 microcontroller.The error signal is then determined and used for a voltage-controlled amplifier that controls the diffraction levels of an acousto-optic modulator(AOM)attached to the system.This allows for the intensity of the first order of diffracted laser beam to be controlled by the closed-loop feedback system.The system's response time is measured and observed to be less than 13 ms,and noises that affect the laser power and measurement systems are observed and analyzed.Experimental data shows that the system can achieve a high level of stability of the output laser intensity,keeping the output within 2% of the set-point(SP).The system is irrespective of the environmental fluctuations,showing the enhancement in the system's performance compared to that in the free-running mode,providing possibilities for use in precision measurements.The system can be incorporated into larger apparatuses as a single functional module to control the laser output programmatically.The system is suitable for experimental research that requires a stabilized laser intensity output and a simplified setup.It has enormous potential and wide applications in precision measurements such as non-destructive surface analysis of mechanical parts,optical magnetometers,biomedical inspections,and liquid and gas composition detection and measurements.