Laser Induced Damage Threshohld (LIDT)

Introduction

Laser induced damage threshold (LIDT)


Contactless wavefront-based characterization of surface characteristics modification
QWLSI can be used for laser damage detection and analysis of laser-induced modification of semi-transparent optical materials. QWLSI can highlight modifications in the material, such as refractive index variations, birefringence effects related to stress or thickness differences.

SID4 Imaging is suitable for both small samples, that require high sensitivity (e.g. optical thin films) but also for macroscopic samples, that require high dynamics (e.g. large optical elements).

Single shot measurement is of high interest in the understanding of the dynamics of physical process. Eventually, SID4 Imaging can be integrated on multiple different setups, and even be used for pump–probe experiments.
 
Where microscopic techniques are only visual and qualitative (e.g. Differential Interferential Contrast), SID4 Imaging provides a quantitative measurement.

Comparisons to other techniques

MethodQuantitativeIn-line
SID4 Imaging
DIC
Optical interferometer

Advantages

  • Off-line and In-line observations
  • Nanometric accuracy
  • Single shot
  • Pump-Probe compatible
  • High dynamics
  • Plug & Play on any experimental setup
  • Filters compatible to eliminate high power laser

Achievements

The refractive index or surface modification of the samples under test has been compared to classical metrology instruments used for laser damage or laser ablation characterization (a differential interference contrast microscope, and an optical surface profiler).

Test conditions: Laser-created Craters on Fused Silica at 1030 nm, incident angle of 45° at various fluence – scale bar: 10µm – [Courtesy of L. Gallais et Douti.-Fresnel Institute]

Surface topography maps obtained with the in-line wavefront sensor (left column) and the optical surface profiler (middle column) on laser-irradiated sites on the silica sample. Each line corresponds to the same sites observed by the different techniques.

Examples

Comparison of depth measurements obtained with QWSLI and the optical surface profiler. Two profiles are also reported. The first one with an emphasis on the rims and the other one on the depth measurement

Comparison of depth measurements obtained with QWSLI and the optical surface profiler. Two profiles at the extremes of the investigated range of fluence are given.

Introduction

  • Four replicas are generated by the diffraction grating.
  • The replicas create an interferogram on the CCD sensor
  • The phase is encoded in the interference fringe deformation
  • Fourier analysis provides phase and intensity maps

LIDT Principle

Note: a reference phase image is acquired before irradiation. So the measurement is free from any perturbation introduced by the imaging system

Set Up

Scientific publications

Applied Optics Vol. 54, Issue 28, pp 8375-8382

DOI: 10.1364/AO.54.008375

Quantitative phase imaging applied to laser damage detection and analysis