FS: Hi-Power AR Lens Assy- 25-30% Inc. vs. Aixiz

edison said:

Hello guys

I found a document in Word on the internet:


Circularize the laser diode beam using cylindrical lens

Cylindrical lenses focus or expand light in one axis only. They can be used to expand the output of the laser diode into a symmetrical beam. The rectangular cross-section of the laser diode cavity results in a beam shape with a wider angular output from the narrow cavity dimension and a narrower angular output from the wide cavity dimension. Laser diodes have an asymmetric radiation pattern which, when collimated, becomes an elliptical beam pattern. As a result, anamorphic prism pairs are often used to convert the elliptical collimated beam to a circular shape.

One can also use a pair of cylindrical lenses to achieve similar results to the anamorphic prism pairs. One cylindrical lens can be used to collimate the laser diode’s slow axis and a second cylindrical lens can be used to collimate the fast axis. By simply matching the laser diode beam divergence ratio (vertical vs. horizontal) to the ratio of the focal lengths of the two lenses, a nearly symmetrical circular beam can be created.

Since a laser diode is considered as a point source, the two lenses should be placed a distance equal to their respective focal lengths from the laser diode emitter orthogonally to create a collimated beam output. Make sure the beam size at each lens does not exceed the clear aperture of the lens. The output beam width is equal to 2f tan Θ (where Θ is beam divergence).

Below is an example of how to match the laser diode beam divergence ratio with the focal length ratio of two cylindrical lenses to create a nearly circular beam.

Specifications of the Thorlabs HL6320G, 635nm, 10mW Laser Diode
G1 = 11 Divergence x-axis FWHM (deg)
G2 = 37 Divergence y-axis FWHM (deg)
Divergence ratio: 3.364

Specifications of cylindrical lenses
F1 = 50.0mm Thorlabs’ LJ1695L1
F2 = 12.7mm Thorlabs’ LJ1942L1
Focal length ratio: 3.937

Specifications of output beam
d1 = 2f1 tan (G1) = 19.44mm
d2 = 2f2 tan (G2) = 19.14mm

As you can see, the output beam is slightly asymmetric but with a great improvement on the beam shape quality.


Maybe this could be of any help to calculate the cilindrical lens.

You only have to fill in the formule for the x-as (fast axis)

Larry measured 40 degrees.

Who is a wizzkid

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LarryDFW said:

After talking with a optics specialist, I don't think the anamorphic prisms are a good solution either. He told me that losses would be >25% with the prisms.

I am still playing with cylindrical lenses after the aspherical.
I think it will give the most circular beam and power.

This is the Hi-Power aspherical lens set-up I got the best results & power with.
It has a steel aperture mounted on the lens assembly, right in front of the diode:

It minimizes the fast axis of the 445nm diode creating a slightly better beam pattern.

LarryDFW
445 "Direct-Drive" Member

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planters said:

I am interested in purchasing a group of 10 to 20 matched lenses for collimating an array of 445 nm diodes. The array is 30 mm on a side so beam dia. is not important but collimation is. Optima supplies molded aspheric lenses with smaller NA and longer FL than your Hi Power lens. Would they be s better fit for this application or could I go with the Hi Power?

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