# Sensitive Displacement Sensor Based on a Flexible Grating Random Laser

## TL;DR

A flexible displacement sensor using a random laser is developed, showing high sensitivity to small movements by detecting changes in laser output.

## Contribution

A novel flexible grating random laser sensor is introduced for high-sensitivity displacement detection.

## Key findings

- The sensor achieves a linear displacement-intensity correlation with R2 ≈ 0.91.
- Lasing threshold is ~21 mJ/cm2 with a linewidth of ~0.25 nm and polarization of ~0.82.
- Micro-displacement alters grating morphology, affecting photon trapping and laser output.

## Abstract

This study proposes and demonstrates a highly sensitive displacement sensor based on a flexible random laser. The sensor utilizes a polydimethylsiloxane (PDMS) film where a self-assembled surface grating structure is formed via oxygen plasma surface treatment combined with bending prestress. This structure acts as a photon-trapping microcavity and multiple scattering feedback center, integrated with embedded laser dye PM597 as the gain medium to form a flexible grating random laser. Experiments show that the device generates random lasing emission under 532 nm pumping (threshold ~21 mJ/cm2) with a linewidth of ~0.25 nm and a degree of polarization of ~0.82. Applying micro-displacement alters the PDMS film curvature, subsequently changing the grating morphology (height, angle). This modifies photon trapping efficiency and geometric deflection loss within the equivalent resonator cavity, leading to significant modulation of the random laser output intensity. A linear correspondence between displacement and lasing intensity was established (R2 ≈ 0.91), successfully demonstrating displacement sensing functionality. This scheme not only provides a low-cost method for fabricating flexible grating random lasers but also leverages the extreme sensitivity of random lasing modes to local disordered structural changes, paving the way for novel high-sensitivity mechanical sensors and on-chip integrated photonic devices.