The laser induced damage threshold (LIDT) of an optical component is dependent on wavelength, pulse duration, and beam diameter. If an optic’s specified LIDT is at a different wavelength, pulse duration, or diameter than that of the application, the LIDT must be re-evaluated at the application specifications. For small changes in these specifications, the resulting scaling of LIDT can be approximated. The larger the difference between the test conditions and the use conditions, the less accurate the scaling. This calculator takes a given LIDT value for a pulsed laser at a known wavelength (λ_{1}), pulse duration (τ_{1}), and beam diameter (∅_{1}), and scales it to a new LIDT at a different wavelength (λ_{2}), pulse duration (τ_{2}), and beam diameter (∅_{2}).

- ± 5% of input wavelength
- ± factor of 3 of pulse duration
- ± factor of 2 of beam diameter

$$ \text{LIDT} \! \left( \lambda_2, \tau_2, ∅_2 \right) \approx \text{LIDT} \! \left( \lambda_1, \tau_1, ∅_1 \right) \times \left( \frac{\lambda_2}{\lambda_1} \right) \times \sqrt{\frac{\tau_2}{\tau_1}} \times \left( \frac{∅_1}{∅_2} \right)^2 $$

λ_{1} |
Wavelength of known LIDT |

λ_{2} |
Wavelength of new LIDT |

τ_{1} |
Pulse duration of known LIDT |

τ_{2} |
Pulse duration of new LIDT |

∅_{1} |
Beam diameter of known LIDT |

∅_{2} |
Beam diameter of new LIDT |

**Question:** What is the approximate LIDT of an optic at a wavelength of 515nm, pulse duration of 30ns, and beam diameter of 2mm if the optic has a specified LIDT of 10 J/cm^{2} at a wavelength of 532nm, pulse duration of 20ns, and beam diameter of 3mm?

**Answer:** The approximate LIDT at the new use conditions can be determined by:

\begin{align}

\text{LIDT} \! \left( 515 \text{nm}, 30 \text{ns}, 2 \text{mm} \right) & \approx 10 \tfrac{\text{J}}{\text{cm}^2} \times \left( \frac{515 \text{nm}}{532 \text{nm}} \right) \times \sqrt{\frac{30 \text{ns}}{20 \text{ns}}} \times \left( \frac{3 \text{mm}}{2 \text{mm}} \right)^2 \\

& = 26.7 \tfrac{\text{J}}{\text{cm}^2}

\end{align}

The approximate LIDT at the new use conditions will be more than 2X higher than the LIDT at the test conditions.

* * Application Notes

Understanding and Specifying LIDT of Laser Components

Importance of Beam Diameter on Laser Damage Threshold

Why Laser Damage Testing is Critical for UV Laser Applications

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