Laser Distance Measurer

Group Members

Arya Chowdhury, Liu Sijin, Jonathan Wong

Experimental Work

2.1 Procedure

2.1.1 Laser Modulation and System Initialization

Configure the function generator (Tektronix AFG1022) to output a 10 MHz square wave with an amplitude of 0–3.1 V (High level: 3.1 V, Low level: 1.0 V, output impedance: 50 Ω) to modulate the laser diode. Use the Keithley 2231A-30-3 DC power supply to provide 5.0 V to the laser driver circuit, with a current limit of 30 mA. Verify the laser beam stability to avoid multimode noise or thermal drift that could distort the modulation waveform.

2.1.2 Optical Alignment and Target Illumination System

Mount the 650 nm laser diode and use a convex lens to collimate and focus the beam onto the reflective target surface. Insert a bandpass optical filter (center wavelength: 650 nm, bandwidth: 10 nm) into the return path to suppress ambient light interference. Fix the reflective target (diffuse or specular surface) on a precision linear translation stage, ensuring proper alignment for beam return to the detector at all positions.

2.1.3 Detection and Amplification Circuit Configuration

Use a Hamamatsu S5971 silicon photodiode to detect the reflected light signal.Connect the detector output to a matched high-speed preamplifier (bandwidth >100 MHz, gain ~10³–10⁵) to amplify the signal linearly without saturation.Connect the amplifier output to Channel 2 of a digital oscilloscope; connect the reference signal from the function generator to Channel 1 as the modulation phase reference.

2.1.4 Static Testing: Time Delay vs. Distance Mapping

Fix the reflective target at several predefined positions along the translation stage (e.g., every 5 cm) and record the waveform signals from both channels at each position.Use the oscilloscope’s cursor measurement function to determine the relative time delay Δt between the modulation reference signal (Channel 1) and the return signal (Channel 2).Correlate the measured delay values with corresponding distances to establish the system’s delay–distance response curve.

2.1.5 Dynamic Scan Testing: Continuous Distance Response Verification

Move the target along the sliding rail at a constant speed, and continuously record the time delay of the return signal at multiple positions. Configure the oscilloscope trigger conditions to ensure stable waveform acquisition. Plot the variation of time delay as a function of target position to analyze the linearity and temporal resolution of the system.

2.2 Measurement techniques

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