This paper reports the results of interferometric characterization of a bimorph deformable mirror (DM) designed for use in an adaptive optics (AO) system. The natural frequencies of this DM were measured up to 20 kHz using both a custom stroboscopic phase-shifting interferometer as well as a commercial Laser Doppler Vibrometer (LDV). Interferometric measurements of the DM surface profile were analyzed by fitting the surface with mode-shapes predicted using classical plate theory for an elastically-supported disk. The measured natural frequencies were found to be in good agreement with the predictions of the theoretical model.
INTRODUCTIONOriginally developed to remove atmospheric distortion from astronomical imaging systems, adaptive optics (AO) has seen more recent application to ophthalmologic instruments and free-space optical communication systems. In each of these applications, the AO system uses a deformable mirror (DM) to correct for optical aberrations by removing phase distortions from the incident wavefront. Since the existing DM technology developed for astronomy is expensive and bulky, recent research has focused on using MEMS technology to create a more compact, low-cost DM. Several MEMS DM designs have been demonstrated, including: membrane-based (OKO Technologies Inc.) [1]; polysilicon surface-micromachined (Boston Micromachines Inc.) [2]; bulk silicon (Iris AO Inc.) [3]; and piezoelectric monomorphs (JPL) [4]. Many MEMS DM designs have been driven by the motivation to produce DMs with hundreds or thousands of actuators. For applications which require the correction of only low-order aberrations (such as defocus, astigmatism, coma, and spherical aberration), a DM with less than 100 actuators may be the best choice, as