Laser Interferometer Systems Position Calculations – Product Fact Sheet

Keysight Laser Interferometer Systems Position Calculations

The Keysight Technologies, Inc. laser interferometer systems allow precise measurement and control of position. The fundamental output of these systems is an integer value, representing the number of uncompensated fractional wavelength counts corresponding to the change in optical distance between two optical components. It only takes some simple math to translate this abstract integer number into a value with real meaning to the user.

Key features

• High precision measurements, but output is an integer
• Simple math used to translate integer into a position in “human” units
• Should compensate for any dead path (DP) in the optical setup

Reset at position 0 and then move to position A Position 0 Position A DP distance 10702A Linear interferometer What does 4328943 really mean?

It could be 1337.617 μm, or 5350.469 μm, or something else depending on type of laser axis board used, the Comp Num and if there are changes during the measurement.

Calculating position from raw interferometer data 1. Fundamental position equation: Example for 25 mm Dead Path, Linear Optics, Standard Air at end but Comp Num was 2 ppm less at start: 1. Values depend on axis board and optics type used. See pub# 5990-8206EN and 5990-9943EN. Example for Linear optics (Optics Fold Factor = 2) and N1231B electronics (Resolution Extension = 1024): 2. This is value for “Standard Air” at 20 °C, 50 %RH, and 760 mmHg (101.3250164 kPa). Actual Comp Num will vary with the environmental conditions. 2. Use fundamental equation twice to compensate for measured DP Distance (simulates move with 0 dead path): 25,000 µm 1024 2 DP Counts 80,907,891 counts 0.63299137 µm 0.99972670 × × = = × 0.99972870 4,328,943 80,907,891 0.63299137 ( ) µm Position 25,000 µm 1024 2 ×+ × = − × Position 1337.667 µm = Initial Comp Num DP Counts Lambda DP Distance solve for DP Counts Resolution Extension Optics Fold Factor × × = × Comp Num (Accumulated Counts DP Counts) Lambda Position DP Distance Resolution Extension Optics Fold Factor × +× = − × Comp Num Integer Counts Lambda Position Resolution Extension¹ Optics Fold Factor¹ × × = × 0.99972870² 4,328,943 0.63299137 µm Position 1337.617 µm 1024 2 × × = = ×