# Design and Calibration of a Slit Light Source for Infrared Deflectometry

## TL;DR

This paper presents a new infrared slit light source design for measuring curved surfaces with high accuracy and efficiency in optical workshops.

## Contribution

A novel infrared slit light source design using a polyimide heating film cavity for stable, uniform, and low-noise measurements.

## Key findings

- The slit light source achieves 1 µm RMS measurement accuracy suitable for grinding processes.
- The design reduces background noise and ensures uniform light emission.
- The light source can also function as a calibration board for infrared cameras.

## Abstract

Infrared deflectometry is an efficient and accurate measuring method for curved surfaces fabricated via grinding or finish milling. The emitting properties and geometrical configurations of the infrared light source is a core component governing the measurement performance. In this paper, an infrared slit light source is designed based on the cavity structure of a polyimide heating film. This design ensures good stability and uniformity of the light source whilst effectively reducing background noise. Additionally, the light source can be applied as a calibration board for calibrating infrared cameras. The light source is aligned using a theodolite and cubic prism to control the positional deviations during scanning. Experimental results demonstrate that the proposed slit light source and calibration method can achieve a measurement accuracy of 1 µm RMS, which can meet the needs of rapid measurement in grinding. This approach provides a reliable, cost-effective, and efficient tool for surface quality assessments in optical workshops and has a broad application potential.