HP 5528A User Manual

Model 5528A
Appendix A; Prin cip les of Operation
A-6
Distance and Velocity Measurements
Th e F1 and F2 beams that leave Ih e laser H ead are aimed al an Inl erferomter which sp lits Fl a nd
F2 via a po larizing beilm spl itt cr. ( See Figure 1\-2). Compo nent Fl becomes the fi xe d-distilnce
path, and F2 is se nt 10 a larget which reflects it back to the Inte rf erometer . Relative motion
between the I nterferometer and the remo te Retrore fl ectorcauses a Doppler shift in the returned
frequency.
Th erefore, the Measureme nt Re cei ve r photode tect or in the l aser Head seeS;1 f rin ge
diff erence given by fl - F2 ± aF2.
The F1 - F2 ± llF2 sig nal that is returned from th e external Interf erometer is compared in the
Measurement Di
sp la y unit to the Fl - F2 Reference sig na l. Th e difference, dF2, is then related
electronically to ve locity and then to distance. This information is finally manipulat cd as
described above under "G ENERAL SYSTEM PR INCI PLE S" to produ ce the co rr ect ou tput on the
di
sp la y.
Proper se paration between outgoing and incoming la se r beams is provided by eac h Retro-
reflector.
REFERENCE
RETROAEFlECTOR
MEASUREMENT
/'- AETROREFlECTOA
/
h
"-
I,
I,
V
I,
"-
FROM LASER
1/
>
TO
I,
f 2 ± ~ 1 2
'2 i ~ 1 2
PH OTO DETECT OR
~ LINEAR INTERFER O ME:'
FIgure A-2. D,sfance and Velocity Measuremenls
Angular Measurement s
The se t- up for making an Angular measurement is shown in Figure 1\-3.
The Angular Opt i cs creilte two para ll el beam paths between the Angular Interferometer and the
Angular R
eflecto r; one pa th is frequency", the second path is frequen cy f2. The distance
between the t
wo paths is preci se ly kn own, since the two Retrorefieclors are precisely positioned
within lhe Angular Reflector. Initially, the angle between the Angular Interferometer and the
Angular R
eflecto r is ass um ed to be "0", and the t wo paths between them have some relative
length.
If either the Angular Int erferometer or the Angular Reflector is turned, the relative
length s of Ihe two paths will change: th is change will cause a Doppler-shilled frequency change
in the beam
t ha t is r et urn ed from the Angular Interferom eter to the L ase r Head. The Laser
Mea s ur ement Syste m 's Elec tr oni cs hardware wi ll ca lcu late and displ ay the angular change, using
the n
ew frequency co unt data and th e spacing between the opt ica l path s.

HP 5528A Specifications

General

Brand	HP
Model	5528A
Category	Measuring Instruments
Language	English