A photomultiplier tube (PMT) is a device commonly used to measure the intensity of light. It operates based on the principle of converting photons into electrical signals.
To determine the intensity of light using a photomultiplier tube, you need to follow these general steps:
Set up the photomultiplier tube: Connect the PMT to appropriate voltage sources and amplifiers as per the manufacturer's instructions. Ensure the PMT is well-calibrated and properly aligned.
Incident light on the PMT: Direct the light you want to measure onto the photocathode of the PMT. The photocathode is a photosensitive surface that emits electrons when illuminated by photons.
Electron multiplication: When the photons strike the photocathode, they release photoelectrons. These electrons are then multiplied through a series of electron multiplication stages within the PMT, typically through a process called electron avalanche multiplication.
Output signal: The multiplied electrons are collected and converted into an electrical signal by the PMT. The amplitude of this signal is proportional to the intensity of the incident light.
Calibration and measurement: Calibrate the PMT by comparing the output signal to known light intensities. This allows you to establish a relationship between the PMT output and the incident light intensity. Once calibrated, you can use the PMT to measure the intensity of unknown light sources.
Regarding your specific question about 400 nm and 800 nm light with the same amplitude, it's important to note that the intensity of light is not solely determined by its wavelength or amplitude. The intensity is a measure of the power carried by the light per unit area. The amplitude of the electric field alone does not directly correlate to intensity.
When two light waves with different wavelengths but the same amplitude are incident on a photomultiplier tube, the detector will not necessarily detect the latter light with twice the intensity. The intensity of light depends on various factors, including the number of photons incident on the PMT per unit time, the wavelength-dependent sensitivity of the PMT, and the quantum efficiency of the photocathode for different wavelengths.
To accurately compare the intensities of light at different wavelengths, you would need to consider the spectral response and calibration of the specific photomultiplier tube being used. Additionally, the intensity of light is generally measured in terms of power (Watts) or radiant flux (Watts per unit area), not solely based on the amplitude of the electric field.