William(familiarly known as Bill by all his colleagues)Yen's life-long scientific interest in the magnetic properties of rutile structured antiferromagnetic materials(AFMs)began with his involvement in the discovery in 1965 of the magnon sidebands of MnF

2

in optical absorption

[1]

.A basic outline of this discovery is given elsewhere in this special issue of the Chinese Journal of Luminescence

[2]

.A narrative discussion of events leading to this discovery appears in a contribution written by Bill and Robert White for a special edition of Low Temperature Physics on Antiferromagnetism

[3]

.A quote from that remembrance highlights a quality that remained with Bill throughout his career:"The identification of these sidebands by a pair of young students and two post-docs illustrates how serendipity

a touch of good luck and reckless youthful enthusiasm often plays a role in scientific discovery".Bill's forever youthful enthusiasm coupled with creative insights into current research questions led to numerous pioneering discoveries throughout his career.This paper reviews Bill's contributions to developing techniques to

exploit dichroism to study the magnetic properties of AFMs.Bill's publications in this area span more than 30 years

from 1971 to 2004.