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We demonstrate a new method for the characterization of high-numerical-aperture lenses based on the f luorescent detection of the spatial autocorrelation of the focal field. Numerical calculations without any fitting parameters, based on scalar diffraction theory, are in excellent agreement with the experimental results. The novel method provides lens characterization parameters similar to those obtained with pointspread function measurements in real time, which may be expected to be suitable for high-numerical-aperture lens testing and alignment procedures. © 1995 Optical Society of America The imaging properties of a high-numerical-aperture (high-NA) lens are generally given in terms of the lens’s optical transfer function or, equivalently if the imaging process is linear in the detected quantity, by the Fourier transform of the optical transfer function, the point-spread function (PSF). These functions express the ability of the lens to transfer spatial frequencies. Measurement techniques for the PSF of high-NA lenses include, among others, three-dimensional imaging— and subsequent analysis—of highly scattering, or f luorescing, spheres that are much smaller than the typical width of the PSF 1‐4 either in full field or by scanning the sphere or the detector. Alternatively one can image the edge of a mirror in ref lection, although some care must be taken in comparing ref lection with f luorescence measurements. 4 The major drawback of these techniques is that they are slow and consequently require long-term nanometer stability of the optical setup. Also, the sample preparation imposes certain constraints on these methods. For optimization of high-NA lens systems, industrial testing of objectives, and three-dimensional image restoration techniques 5 a real-time technique would be useful for lens characterization. In this Letter we demonstrate a new technique, the point-spread autocorrelation function (PSAF) technique, which provides a straightforward, accurate, and versatile alternative for real-time characterization of high-NA lenses. First we introduce the new functional dependence in general terms, after which we demonstrate the capabilities of the technique, using theoretical modeling and experimental verification. In the novel PSAF technique we introduce a new function, GsDr, td, for the characterization of optical lens properties based on the measurement of the autocorrelation of the focal field of a (high-NA) lens:

Characterization of high-numerical-aperture lenses by spatial autocorrelation of the focal field