Agilent laser interferometer

We are using an Agilent laser interferometer system. The laser head will sit outside the chamber, and the beam will be brought in through a regular conflat flange with a glass window. Inside the chamber there will be beam splitters for dividing the beam up into three equally strong components. Each microscope axis ($x/y/z$) is equipped with a differential interferometer head (Agilent 10715A) which will measure the relative position of the sample on the PI piezo stage relative to the zone plate. The signal from these heads will be carried by fibers with a vacuum feedthrough to receiver units located outside the chamber (the decision to commit to fiber is still to be made). The interferometer signals from all three axes then go into a single Agilent PCI card (N1231A) in the PC. The positions and velocities can be read by the computer directly over the PCI bus, and the positions are also available on a continuous basis as 24 bit parallel words which will be fed into the Delta Tau boards.

The interferometer precision is $\lambda$/2048 or 0.3 nm. The 24 bit Delta Tau position range is then 5 mm, while the 32 bit position range available on the PCI bus is 1.2 m.

The following details from the file stxm5/agilent/N1231-90002_000502.pdf are of particular interest to us:

• The minimum step size depends on the interferometer type. We're using a plane mirror, so the minimum step size is $\lambda$/2048 or 0.3 nm (see p. 6-3 which is p. 57 of the PDF file). The 24 bit Delta Tau position range is then 5 mm, while the 32 bit position range available on the PCI bus is 1.2 m.

• The positions and velocities of the three axes are available in registers on the PCI board as described on p. 3-3 which is p. 37 of the PDF file. C/C++ header files for programming are listed in Appendix B.

• The board updates positions and velocities internally every 50 nsec (see p. 6-3 which is p. 57 of the PDF file). The time to deliver 3 position and velocity values on the PCI bus appears to be 7.5 $\mu$sec (see p. 6-5, which is p. 59 of the PDF file).

• For handshaking of digital position information with the Delta Tau PMAC module, the PMAC raises its OCLK output to indicate that it would like to receive a new value of the axis position. The Agilent board then loads its present 24-bit position for the axis about 100 nsec later. 200 nsec after that (or 300 nsec after the Delta Tau board raised OCLK), the Agilent board raises its ICLK line for 200 nsec to indicate that its position output bits are stable. This process is shown on p. 6-6 (PDF file page 60) of the Agilent manual.

  On the Delta Tau ACC-14D board, the OCLK1 output is on connector J7 pin 48, and OCLK2 is on connector J15 pin 48. The ICLK1 input is on connector J7 pin 46, and ICLK2 is on connector J15 pin 46.

Finally, some example .h and .cpp files for C++ programming are at src/agilent/. They come from the file N1231-13602-1 Rev A.00.00 Install CD from the Agilent web site.