# Intensity of coherent/incoherent light

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• MFAHH
In summary, the question is about estimating the relative intensities of coherent and incoherent light in a 3-level laser device. The answer to the second part is that the photon energies do not change, but spontaneous emission in the lower transition can become relevant. The 694nm wavelength is from the pumping process, while the 2700nm wavelength corresponds to the difference between the intermediate and lowest state. The emitted pumping-related photon is approximately one per laser photon.
MFAHH
Here's a question I'm working on. I've managed everything uptil the first bolded part, then I get stuck there. I have no idea how to estimate the relative intensities of coherent and incoherent light. I've had a look at tonnes of formulas for the intensity of light but can't find one which would work here. Any help?

And for the second part I've made bold, is the answer to that question: photon energies and coherence of the emitted light do not change?

Question: In a 3-level laser device two different energies of light are emitted. Coherent light is observed with a wavelength of 2700nm and incoherent light with a wavelength of 694nm. Use the above information to sketch the energy levels of the 3-level laser system. Label the energies (in eV) of each of the excited levels relative to the ground state. You may assume that the lowest energy level is the ground state of the atom.

If an optical flash is used as the mechanism to excite the three level laser system what wavelength of light should be used?

Estimate the relative intensity of the coherent and incoherent light produced by the laser.

Consider a situation in which the photon density of the lasing cavity is very significantly reduced, for example by reducing the reflectivity of the surfaces of the lasing cavity. How would you expect the photon energies and coherence of the emitted light to change?

The photon energies don't change, but spontaneous emission in the lower transition can become relevant.

I guess the 694 nm are from the pumping process, so they go from the highest to the intermediate state, while 2700 nm corresponds to the difference between intermediate and lowest state. This also means up to one emitted pumping-related photon per laser photon.

## What is the difference between coherent and incoherent light?

Coherent light is light that has a fixed phase relationship between its waves, meaning that the peaks and troughs of the waves are aligned. Incoherent light, on the other hand, has no fixed phase relationship and the peaks and troughs of the waves are randomly distributed.

## How is the intensity of coherent light different from incoherent light?

The intensity of light refers to the amount of energy that is transmitted through a given area in a certain amount of time. Coherent light has a higher intensity than incoherent light because the waves are aligned, allowing for constructive interference and a stronger overall signal.

## What factors affect the intensity of coherent light?

The intensity of coherent light can be affected by several factors, including the power and wavelength of the light source, the distance between the light source and the target, and any obstructions or scattering that may occur along the path of the light.

## How is the intensity of coherent light measured?

The intensity of coherent light is typically measured using a light meter, which detects the amount of light energy hitting a specific area. The unit of measurement for intensity is watts per square meter (W/m2).

## What are some practical applications of understanding the intensity of coherent light?

Understanding the intensity of coherent light is important in various fields, such as optics, telecommunications, and laser technology. It is also crucial in medical imaging techniques, such as optical coherence tomography, which uses coherent light to produce high-resolution images of tissues and structures within the body.

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