ISO S-on-1 LIDT test (21254-1,2)

S-on-1 test explained:

Use this test for:

• Specification of “typical” LIDT numbers of your optics;
• Characterization of “fatigue-driven” laser damage to see if optics performance is changing in time;
• Investigation of possible failure modes (damage mechanisms) that might develop over time;
• Examination of the optic’s lifetime (in combination with prolonged exposure and data extrapolation);

Test description

The entrance surface of the optical element is divided into a matrix of test sites. Each test site is then exposed to a burst of laser pulses with fixed laser peak fluence. Distinct fluences levels are used for individual test sites. During irradiation sample is monitored for damage: if the damage is detected irradiation is stopped and the dose required to trigger damage is recorded. Otherwise, if samples survive a maximum number of S laser pulses irradiation is stopped for that test site. After exposure, the status of all test sites is also inspected with offline microscopy. Collected damage statistics are then used to calculate LIDT dependence versus the number of applied laser pulses (exposure dose).

Known limitations and risks:

• Not possible for very limited surface samples (fibers, testing areas <1mm, etc.: use R-on-1 instead);
• Not repeatable/Overestimates LIDT for samples with a very large aperture (extremely low defect density: use raster scan instead);
• Testing at very high repetition rates might cause annealing or contaminations of neighboring test sites. Thus, LIDT can be overestimated or underestimated;
• Testing with less than 1000 pulses is only suited to characterize defect-driven damage mode (long-term degradation effects require a much higher irradiation dose.

Most popular test parameters for this test

⁽¹⁾ effective pulse duration measured at Full Width Half Maximum