# Beam Divergence from non-circular laser beam

• nordmoon
In summary, the laser beam is not a point source and has a rectangular shape with a divergence of 30 mrad x 1 mrad. To find the size of the laser lobe at a distance of 250 mm from the source, trigonometry can be used by taking into account the angle of the rectangle. However, if the spatial width of the laser beam at the exit is larger than the calculated values, the size of the lobe may be different. Additionally, if the laser is coupled into an elliptical waveguide, the beam will have a divergence of 70 mrad x 1 mrad.
nordmoon

## Homework Statement

The laser beam is not a point source. It is known that it has a rectangular shape with a divergence of 30 mrad x 1 mrad. I would like to know how large my laser lobe will be at a distance of 250 mm from the laser source.

## Homework Equations

I think you can use trigonometri for a triangle. tan(A) = opposite/adjacent

## The Attempt at a Solution

The angle of the rectangle will be half of angle of the divergence spread since the divergence is linear.

opposite = adjacent * tan(A), thus

opposite_height = 250 mm * tan(15mrad) = 3.75 mm
opposite_width = 250 mm * tan(15mrad) = 0.125 mm

Thus, the laser beam or lobe should have the size of 2*3.75 mm x 2*0.125 mm = 7.5 mm x 0.25 mm at a distance of 250 mm from laser source.

Correct?

Last edited:
Only if the spatial width of the laser beam at the exit is much smaller than those values. Otherwise you have to take this into account. If your laser exit has a width of several millimeters, a small divergence won't mean your beam magically shrinks to 0.125 mm.

What do you mean by "angle of the rectangle"?

Well, ok.. so a laser diode is coupled into an optical waveguide that is very elliptical in shape, giving a lobe shaped beam with divergence of 70 mrad x 1 mrad.

## What is beam divergence?

Beam divergence refers to the spreading out of a laser beam as it travels away from its source. This is caused by the natural tendency of light waves to spread out as they propagate through space.

## How is beam divergence measured?

Beam divergence is typically measured in milliradians (mrad) or degrees (°). It can be calculated by measuring the beam diameter at two different distances from the source and using the formula: divergence = (beam diameter at farther distance - beam diameter at closer distance) / distance between two measurements.

## Why is beam divergence important?

Beam divergence is an important factor to consider in laser applications because it determines the size and shape of the laser beam at different distances from the source. This can affect the accuracy and precision of the laser and its ability to deliver energy to a specific target.

## How does the shape of a laser beam affect its divergence?

The shape of a laser beam, specifically its cross-sectional profile, can have a significant impact on its divergence. Non-circular laser beams, such as elliptical or rectangular beams, tend to have different divergence characteristics compared to circular beams.

## What factors can affect beam divergence?

The most common factors that can affect beam divergence include the type of laser used, the optical components and alignment of the laser system, and environmental factors such as temperature and air turbulence. Proper design and maintenance of the laser system can help minimize beam divergence.

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