---
title: "Two-Photon Action Cross-Section calculator — AperiOptic"
description: "Effective excitation rate from σ2·η at given peak intensity. Free online optics calculator, with the formula and code snippets."
url: "https://aperioptic.com/calculators/two-photon-action-cross-section"
---

# Two-Photon Action Cross-Section calculator

Effective excitation rate from σ2·η at given peak intensity.

Category: [Imaging](https://aperioptic.com/calculators)

Formula: `Rate ∝ σ2·η · I²`

## Inputs

| Input | Parameter | Unit | Default |
| --- | --- | --- | --- |
| σ2 (GM) | `sig` |  | 50 |
| Quantum yield η | `eta` |  | 0.8 |
| Peak I (GW/cm²) | `I` |  | 100 |

## Result with the default inputs

- Action σ2·η: 40 GM
- Rel. brightness: 400000

Open it with your own values: put each input in the address as a parameter, for example [`/calculators/two-photon-action-cross-section?sig=50`](https://aperioptic.com/calculators/two-photon-action-cross-section?sig=50). A unit other than the listed one goes in `<parameter>_unit`.

Read more: [Wikipedia: Two-photon absorption](https://en.wikipedia.org/wiki/Two-photon_absorption)

[All optics calculators](https://aperioptic.com/calculators)

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The interactive page: https://aperioptic.com/calculators/two-photon-action-cross-section (AperiOptic runs in the browser; free, no account). Every page of the site as Markdown: https://aperioptic.com/llms.txt