# Single Axial Mode And Spectral Hole Burning

• SSJVegetto
In summary, when light is reflected at a surface, the field amplitude must be zero. In a laser cavity, axial modes are defined by the number of sine-wave half cycles that fit exactly. The optical gain curve of a crystalline solid-state laser typically has a range of 10-100 nm, allowing many axial modes to fall within it and potentially start lasing. However, in a homogeneously broadened gain medium, only one axial mode will start lasing at the pump threshold due to the maximum of the gain curve. The phenomenon of spectral hole burning is related to this and can be further explained by reading a specific tutorial.
SSJVegetto
Reflection at a surface takes place under the condition that the field amplitude is zero at the reflecting surface. As a result, the axial modes i of wavelength λi inside a laser cavity can be defined by their number ni of sine-wave half cycles that fit exactly into the laser cavity. The optical gain curve of the active medium of a crystalline solid-state laser has a wavelength range of typically 10-100 nm, so that many (~104) axial modes inside a few-cm long cavity fall within the optical gain curve and may therefore start lasing.

Can someone explain why nevertheless only one axial mode starts lasing in a homogeneously broadened gain medium at pump threshold?

Can someone explain the phenomenen of spectral hole burning?

Another question is, is there someone who can help me with a few other questions that i send a pm with a pdf file?

...so that many (~104) axial modes inside a few-cm long cavity fall within the optical gain curve and may therefore start lasing.
yes and that is, what typically happens in solid state lasers unless you use a mode-selective element.
why nevertheless only one axial mode starts lasing in a homogeneously broadened gain medium at pump threshold?
The gain curve has a maximum. The mode closest to that maximum will start lasing first. That is the threshold.
spectral hole burning
You may want to read http://www.physics.montana.edu/faculty/rebane/Research/Tutorials/Hole_burning/HoleBurning_00.htm first and then ask more specifically.

## 1. What is single axial mode and spectral hole burning?

Single axial mode refers to a laser cavity that is designed to only have one specific resonant mode, or wavelength, of light. Spectral hole burning is a phenomenon that occurs in laser materials where certain wavelengths of light are absorbed more quickly than others, creating "holes" in the material's absorption spectrum.

## 2. Why is single axial mode important in laser technology?

Single axial mode lasers have a very narrow range of wavelengths that they can emit, making them useful for applications that require precise and stable laser beams, such as in telecommunications, spectroscopy, and laser printing.

## 3. How does spectral hole burning affect the performance of lasers?

Spectral hole burning can have both positive and negative effects on laser performance. On one hand, it can improve the laser's output power and efficiency by reducing the competition between different modes of light. On the other hand, it can also cause instabilities and fluctuations in the laser's output, which can be problematic for certain applications.

## 4. What factors can influence the occurrence of spectral hole burning?

The main factors that can affect spectral hole burning include the laser material's temperature, the intensity of the laser beam, and the duration of the laser pulse. Additionally, the presence of impurities or defects in the material can also play a role in the occurrence of spectral hole burning.

## 5. How can scientists control or mitigate spectral hole burning in lasers?

There are several techniques that can be used to control spectral hole burning, such as adjusting the temperature of the laser material, using shorter laser pulses, or using a different laser material with a wider absorption spectrum. Additionally, advanced laser designs, such as distributed feedback or distributed Bragg reflector lasers, can also help minimize the effects of spectral hole burning.

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