Two-Photon Absorption Calculator
Combine two-photon cross-section with laser intensity to approximate transition probabilities for nonlinear optics experiments.
Use seconds (100e-15 s for 100 fs).
Absorption rate
1.000e-30 s^-1
Absorbed fraction
0.000e+0
How to Use This Calculator
Enter the two-photon cross-section
Use gigamills (GM) units tabulated in experiment or literature.
Provide peak intensity
The correlation assumes peak intensity in GW/cm2. Convert average powers if needed.
Specify pulse duration
Use the pulse width or interaction time in seconds to estimate absorbed fraction.
Review rate and fraction
The calculator outputs the per-molecule absorption rate and the fraction excited during the pulse.
Formula
R = delta * I^2
delta in cm^4 s photon^-1, I intensity in W/cm2. The absorbed fraction f = 1 - exp(-R tau).
Example
For delta = 100 GM, intensity = 1 GW/cm2, tau = 100 fs: R = 100 * 1e-50 * (1e9)^2 = 1e-30 s^-1, f = 1 - exp(-1e-30 * 1e-13) about 1e-43.
Full Description
Two-photon absorption is a nonlinear optical process where a molecule absorbs two photons simultaneously to reach an excited state.
Knowing cross-sections and laser intensities helps plan microscopy, spectroscopy, and photopolymerization experiments.
Frequently Asked Questions
What are GM units?
One GM equals 1e-50 cm^4 s photon^-1. It standardizes reported two-photon cross-sections.
Does the formula include saturation?
No. It assumes linear response at low excitation probability. High intensities may require rate equations.
Should I use average or peak intensity?
Use peak intensity for pulsed lasers. Convert average power using duty cycle or beam parameters.
Can I model continuous wave lasers?
Set tau to the interaction time and intensity to the constant power density.
Why is the absorbed fraction so small?
Two-photon absorption is weak. Significant excitation typically requires high peak intensities or resonant enhancement.