We report on femtosecond pump–probe experiments on two different photoinitiators in solution. These two molecules have recently appeared as attractive candidates for far-field optical lithography based on stimulated-emission- depletion (STED) inspired approaches aiming at beating Abbe’s diffraction limit. For the case of 7-diethylamino-3-thenoylcoumarin (DETC), we find that stimulated emission clearly dominates over excited-state absorption, whereas the opposite holds true for the case of isopropylthioxanthone. We argue that it is desirable that stimulated emission dominates over excited-state absorption as depletion mechanism in STED photoresists. Thus, DETC is an attractive corresponding photoinitiator.
© 2011 Optical Society of America
Original Manuscript: March 15, 2011
Revised Manuscript: May 24, 2011
Manuscript Accepted: July 7, 2011
Published: August 11, 2011
Thomas J. A. Wolf, Joachim Fischer, Martin Wegener, and Andreas-Neil Unterreiner, "Pump–probe spectroscopy on photoinitiators for stimulated-emission-depletion optical lithography," Opt. Lett. 36, 3188-3190 (2011)