The relationship and difference between aperture, local aperture, PV and RMS

May. 31, 2019

The relationship and difference between aperture, local aperture, PV and RMS

Customized Optical Components Manufacturer shares that the surface profile is one of the important precision indexes in optical manufacturing. This is like paving cement pavement, paved the surface is very flat, no potholes, the car drove over the good road is very smooth, not good potholes, it is bumpy! PV and RMS are two parameters of surface type of the Customized Optical Components. PV is the difference between the highest and lowest point of the road surface, and RMS is the average of all the road surface heights. Therefore, PV value can achieve 0.1 wavelength, and RMS value is at least about 0.02. Generally speaking, PV value is 6-8 times of RMS value. At present, many merchants say that the so-called 1/8 wavelength or 1/10 wavelength actually refers to the RMS value, the PV value is often less than 1 wavelength, and good astronomical observation equipment should have PV=1/2 wavelength is considered as a good precision.

In practice, requirements of optical parts in optical drawings are expressed by aperture number (N) and local aperture, while pv and RMS values are detected by zygo interferometer after processing. Zygo can be used to measure aperture, local aperture and pv. The RMS. Different Settings measure different things. It doesn't always come out PVS. The relationship between aperture and PV is: aperture is good. PV must be good. PV. Aperture is not always good. PV is the relative value of the peak and trough of the aperture. Local errors are not considered. The influence of local aperture error should be considered when saying aperture.

Customized Optical Components Manufacturer

Using a ZYGO instrument to measure the aperture (N) of an optical part, the reading is not very accurate. The reading is the power value in the surface map above the software, but the units should be converted into optical units. As for partial aperture, it is very accurate to read pv straight in the profile map. Put the lines in the surface map in the highest and lowest positions and see the proportion of pv occupied by high or low.

The number of apertures in the drawing is the number of interference fringes caused by the deviation between the processing element and the sample plate. When measured by the interferometer, the reference sphere radius (similar to the template radius) is variable, and the number of stripes can be varied. The measurement results (PV and RMS values) are the deviation between the machining element and the closest reference sphere.

A circle is a plane shape deviation of 1/2 wavelength size,546.1nm is the standard wavelength,PV is the maximum of the plane shape deviation, divided by 546.1 is a few wavelength, compared with a half wavelength, a few half wavelength is a few to a circle.

In a word, light circle is one of two different evaluation criteria, PV and RMS. The local aperture, if evaluated as PV, is higher than PV.


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