A novel non-contact multiaxial astigmatic detection system (ADS) is
designed and developed using the astigmatism as the measuring principle for the
translational displacement, the angle, and their variations of a measured
surface simultaneously. An optical pickup unit (OPU) of a commercial digital
versatile disk (DVD) read only memory (ROM) drive can be used directly as an
optical path mechanism in the above mentioned ADS, which can measure the
translational and angular displacements accurately and simultaneously. The
total linear detection range and the maximum measurement bandwidth of the ADS
are 6
mm and 80MHz, respectively. The resolution of the translational
displacement measurement is in sub-angstrom scale. For an operating frequency
of 700 kHz, the noise floors of the translational and angular signals are below
0.8 pm/Hz1/2 and 0.4

rad/ Hz1/2, respectively.

The ADS can monitor the translational and two orthogonal angular
displacements of a micro fabricated cantilever in atomic force microscopy
(AFM). All the three, contact non-contact and tapping, modes can resolve the
single atomic steps of the graphite surface, which indicates that atomic resolution
is achievable with the ADS. The thermal noise spectra of the AFM probe can be
clearly measured as well. Furthermore, the accuracy of scanning probe
microscopy (SPM) depends not only on the measurement system itself, but also by
the accuracy of the signal processing, which further depends on the physical
and geometrical characteristics of the probe.

 The structure of the ADS is
compact and stable. Besides the measurements through AFM probes, the ADS can be
operated in profilometer mode. The CD surface and the CCD microlens are
measured by this mode. The maximum scanning speed can reach up to 3.84
theoretically, almost one million times faster than that of a commercial SPM

The ADS has a great potential for future development, the expansibility
and the accuracy can evolve with the performance of future OPU. From the DVD OPU
to higher resolution one, such as the OPU of the Blu-ray drive or high-
(HD-DVD), can be integrated into the ADS as well.

 KEYWORDS: Astigmatism, ADS,
Translational displacement, Angular displacement, SPM, AFM, Cantilever, Optical

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