AVS 49th International Symposium
    Thin Films Monday Sessions
       Session TF-MoM

Paper TF-MoM9
Measuring Optical Losses in Thin Films with Ringdown Cavity

Monday, November 4, 2002, 11:00 am, Room C-101

Session: Optical Thin Films
Presenter: G. Vaschenko, Colorado State University
Authors: G. Vaschenko, Colorado State University
Y. Godwal, Colorado State University
C.S. Menoni, Colorado State University
C. Montcalm, Veeco Instruments Inc.
R. Blacker, Veeco Instruments Inc.
D. Siegfried, Veeco Instruments Inc.
Correspondent: Click to Email
Optimization of multilayer optical components (such as wavelength division multiplexing (WDM) filters for fiber optics communications) often requires measuring the losses in the individual films composing these optical elements. Ion beam sputtering yields films with optical losses on the scale of parts per million (ppm), which is significantly smaller than the sensitivity threshold of conventional analytical techniques such as ellipsometry or spectrophotometry. In this contribution we demonstrate a new, highly sensitive experimental configuration for the characterization of losses in thin films on optically transparent substrates. Our method is based on synchronous pumping of the ringdown cavity by the pulses of a mode-locked Ti:Sapphire laser. The length of the ringdown cavity is selected to match that of the laser, therefore the pulse inside the ringdown cavity is significantly boosted on every roundtrip. The thin film sample grown on a transparent substrate is introduced in the cavity and aligned exactly perpendicular to the axis of the cavity, so that the light reflected from the sample interfaces is recycled and the reflection loss does not contribute to the total measured loss of the film. The losses are determined by measuring the time dependent decay of the ringdown signal. This method allows us to obtain high signal-to-noise ratio decay signals with small pulse energy and without signal integration over large number of shots. Using this technique we have detected record low single pass loss of only 64 ppm in a 2 mm fused silica substrate and 79 ppm loss in a 4 µm tantalum pentoxide film fabricated with a SPECTOR ion beam sputter system.