the Difference Beam Size vs Clear Aperture

 

the Difference Beam Size vs Clear Aperture

Understanding the design of laser beam structures that utilize beam guidance generation, extra specifically pairing beam steerage set with a laser, is vital for device setups. One of the maximum important components during set up is aligning the clear aperture of the beam steering set with the beam size of the laser. This regularly increases the query between beam size and clean aperture, which I’m going to dissect in this blog, in addition to help you with proper calculations.

One of the maximum not unusual misconceptions in setting up a laser and beam guidance machine is that the clear aperture fee ought to same as the most allowable laser beam length. It’s essential to be aware that clear aperture is a parameter of the optic components, wherein the optical performances are described strictly inside this aperture. Optics overall performance out of doors of the clean aperture are unspecified, in which massive illumination beyond this boundary not only causes power loss, however, will even purpose the optics to do the subsequent:

1.      Deformation of the optic because of excessive boiler

2.      Change in the index of refraction with infection (transmissive optics simplest)

3.      Delamination between the coating and the substrate

4.      Stray mild that can harm different additives of the system

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Typically, lasers emit circular formed beams with a Gaussian profile. By applying beam shaping technology, the Gaussian profile may be transformed right into a Uniform profile (Top Hat), with the output beam formed as a square, rectangular, and many others. The beam length for a Uniform parameter is straightforward (see parent below). Meanwhile, measuring the beamwidth of the Gaussian side view is more subjective and closely dependent on the technique being accompanied. Some of the one-of-a-kind criteria used for reporting a Gaussian beam length to encompass; D4σ, 10/90 or 20/80 knife-side, 1/e2, FWHM, and D86. Where 1/e2 & FWHM (Full-Width at Half-Maximum) are maxima commonly used, understanding the laser beam profile and beam length is critical as the equal laser beam may have a specific beam size based on its definition1.

So, what happens whilst specific beam sizes are carried out to the same clear aperture? Pretty trustworthy, as shown within the determine beneath— whilst the laser beam overfills the clear aperture, the outer-ring portion of the laser beam could be clipped. Which brings us to the subsequent question, what is the precise beam diameter to be carried out for sure clear aperture?

By digging a bit deeper into the maths equations and the usage of a typical Gaussian beam with a beam length defined by way of 1/e2, for example, we will ensure <1% of electricity loss due to beam clipping. See formulas underneath:

Therefore, the incident beam width on the aperture must be:

And with the equal calculation to make certain <10% of energy loss, the clean aperture ought to be as a minimum 1.07 instances bigger than the 1/e2 beam length; for <five% energy loss, it need to be 1.22; and for <0.1% electricity loss, it ought to be 1.86.

Important to notice is that considering that a laser beam size value defined with the aid of 1/e2 is kind of 1.7 times the diameter defined with the aid of FWHM, calculations for the perfect beam size and clear aperture ratios may be produced from the above cases.

Using the Gaussian beam aimed at the example, but in this situation, the beam size is described under FWHM. To make sure <1% of energy loss due to beam clipping, the clean aperture ought to be:

Another point to resolve is the everyday misconception of having the input laser beam length exactly similar to the clear aperture. Applying the equal components and assuming the beam length is defined by way of 1/e2, you are at risk of clipping 13.5% of the power. It’s essential to observe that the amount of energy falling off the mirrors will now not only purpose heat up, delaminate, burn coatings and scatter mild as formerly stated, but may also be deposited onto the internal components within the scan head enclosure or be absorbed by the DFM lens maintaining ring (with glue) and DFM lens holder. In either case, this can purpose major harm to cutting-edge structures at some stage in integration and is particularly vital while working with an excessive-energy laser.

Last, however, no longer least, the above calculations are assuming perfect alignment. In case of real alignment errors, keeping some margins should be taken into consideration.

In the end, always understand that the definition of the input beam length and the clear aperture size is NOT equal. When that is unsuitable, it is able to reason surprising strength clipping, which will negatively have an effect on your device during integration, like a malfunction or maybe a device explosion. When users buy a laser beam steerage solution from us, we offer clear aperture facts, whereas the definition of the laser beam size needs to come with the spec sheet of the laser. In addition, the laser spec sheet may additionally provide laser alignment specifications, inclusive of its laser output function and pointing error. If these aren’t provided, make sure to test with the laser producer to confirm these parameters for fine performance functions. Having examined and efficaciously included exceptional systems throughout multiple programs, we will assure that those pointers will help clear up confusion and prevent future damages.