Enter your **cross-section (δ)**, **laser power (P)**, **wavelength (λ)**, **focus size (w₀)**, and **pulse duration (τ)** into the **Two-Photon Absorption Calculator** to find the **excitation rate (N)** for your fluorophore or nonlinear optical system, along with the underlying **photon flux (φ)** and **peak intensity** driving the absorption event.
Excitation Rate (N)
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Photon Flux (φ)
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Peak Intensity
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Two-photon absorption (TPA) is a nonlinear optical process where an atom or molecule absorbs two photons simultaneously, transitioning from a ground state to a higher energy state. The energy difference equals the sum of the two photon energies.
TPA is nonlinear because the absorption rate is proportional to the square of the optical intensity. This means it only occurs at high light intensities and the absorption coefficient depends on the light intensity itself.
TPA is used in two-photon microscopy for deep tissue imaging, 3D optical data storage, photodynamic therapy, and microfabrication. It enables precise spatial control due to its quadratic dependence on intensity.
The TPA cross-section is typically measured using Z-scan techniques, two-photon excited fluorescence methods, or nonlinear transmission measurements. It's expressed in Göppert-Mayer units (GM), where 1 GM = 10⁻⁵⁰ cm⁴·s/photon.
Photon absorption is the process where matter absorbs electromagnetic radiation (photons), causing electrons to transition to higher energy states. In two-photon absorption, this happens through the simultaneous absorption of two photons.
A free electron cannot absorb a photon in vacuum because this would violate conservation of energy and momentum simultaneously. However, in the presence of a third particle (like an ion), absorption can occur through inverse bremsstrahlung.
The excitation rate depends on the TPA cross-section of the material, laser intensity (quadratically), pulse duration, and focus geometry. Higher intensities and larger cross-sections lead to higher excitation rates.
Yes, TPA can cause unwanted effects like optical limiting, pulse distortion in high-power lasers, and damage in optical components. It can also lead to nonlinear losses in fiber optic communications at high power levels.