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Related Concept Videos

Intensity Of Electromagnetic Waves01:22

Intensity Of Electromagnetic Waves

The energy transport per unit area per unit time, or the Poynting vector, gives the energy flux of an electromagnetic wave at any specific time. For a plane electromagnetic wave with E0 and B0 as the peak electric and magnetic fields and traveling along the x-axis, the time-varying energy flux can be given by the following equation:
Sound Intensity00:58

Sound Intensity

The loudness of a sound source is related to how energetically the source is vibrating, consequently making the molecules of the propagation medium vibrate. To measure the loudness of a source, the physical quantity of interest is the intensity. This is defined as the energy emitted per unit of time per unit of area perpendicular to the sound wave's propagation direction. Since the total energy is greater if the source vibrates for a longer duration and over a larger area, dividing the emitted...
Intensity and Pressure of Sound Waves01:05

Intensity and Pressure of Sound Waves

The intensity of sound waves can be related to displacement and pressure amplitudes by using their wave expressions and the definition of intensity. The critical step to achieve this is to write the power delivered by the particles on the wave as the product of force and velocity and simplify the force per unit area as the pressure. The velocity of the medium's particles can be derived from the displacement.
Unlike the time average of a sinusoidal term, which is zero since it is positive and...

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Related Experiment Video

Updated: Jun 15, 2026

Single Molecule Fluorescence Microscopy on Planar Supported Bilayers
20:00

Single Molecule Fluorescence Microscopy on Planar Supported Bilayers

Published on: October 31, 2015

Determining single-molecule intensity as a function of power density.

Samara L Reck-Peterson, Nathan D Derr, Nico Stuurman

    Cold Spring Harbor Protocols
    |March 3, 2010
    PubMed
    Summary
    This summary is machine-generated.

    Determine optimal excitation power density for total internal reflection fluorescence microscopy (TIRFM) by measuring fluorescence intensity. This ensures the highest signal-to-noise ratio by avoiding dye saturation.

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    Area of Science:

    • Microscopy techniques
    • Biophysics
    • Fluorescence imaging

    Background:

    • Total internal reflection fluorescence microscopy (TIRFM) is a powerful technique for high-resolution imaging.
    • Fluorescence intensity in TIRFM is dependent on excitation intensity and power density.
    • Achieving optimal signal-to-noise ratio requires understanding dye behavior under varying illumination conditions.

    Purpose of the Study:

    • To provide a protocol for determining the saturation point of fluorescent dyes used in TIRFM.
    • To guide researchers in selecting the appropriate excitation power density for maximal signal without saturation.

    Main Methods:

    • Measuring fluorescence intensity as a function of excitation power density.
    • Calculating power density (W/cm^2) based on illumination power and beam area.
    • Identifying the point at which fluorescence intensity ceases to increase linearly with power density.

    Main Results:

    • Fluorescence intensity shows a linear relationship with excitation intensity up to the saturation point.
    • Saturation occurs when the dye spends a significant portion of its time in the excited state.
    • Optimal signal-to-noise ratio is achieved near the saturation threshold.

    Conclusions:

    • A systematic measurement of fluorescence intensity versus power density is crucial for TIRFM optimization.
    • Understanding and controlling excitation power density prevents photobleaching and maximizes signal.
    • This protocol enables researchers to achieve superior image quality in TIRFM experiments.