Laser-Induced Damage Threshold (LIDT)

Long Pulse and cw-Lasers

Long pulse with high average power

Long pulse with high average power

• Absorption because of impurities, structural defects and intrinsic material properties leads to local heating and thermal destruction.
• LIDT is determined by melting point, heat transfer and the purity of the coating.

If heat is efficiently dissipated into the substrate, the component withstands the laser load.

Short Pulses – Pulse Length Scaling

Beam diameter is important

Scaling LIDT

Beam diameter is important

LIDT is usually normalized to beam spot area, but a larger beam will likely illuminate more defects. This may result in a smaller damage threshold.

Scaling LIDT

Scaling LIDT data to different pulse durations using empirical models (e.g., square-root law) may result in deviations of up to 25 %, especially outside tested ranges.

Ultra-Short Pulses – Temporal Pulse Shape

Short pulse with high peak pulse power

Towards shorter pulses intensity becomes the crucial quantity for LIDT.

Quality factors for comparison of LIDT values

Short pulse with high peak pulse power

• Absorption because of transfer of electrons from valence band to conduction band leads to ionization and electronic destruction.
• LIDT is determined mostly by band gap, i.e. material properties.

Towards shorter pulses intensity becomes the crucial quantity for LIDT.

Quality factors for comparison of LIDT values

• Temporal pulse shape q_t: fraction of energy within temporal FWHM
• Lateral beam shape q_A: fraction of energy within lateral FWHM

Comparison of fs-LIDT values, measured with different setups, can be critical because each fs setup has a very unique pulse shape.