Abstract
High-resolution optical imaging within thick objects has been a challenging task due to the short working distance of conventional high numerical aperture (NA) objective lenses. Lenses with a large physical diameter and thus a large aperture, such as microscope condenser lenses, can feature both a large NA and a long working distance. However, such lenses suffer from strong aberrations. To overcome this problem, we present a method to correct the aberrations of a transmission-mode imaging system that is composed of two condensers. The proposed method separately identifies and corrects aberrations of illumination and collection lenses of up to 1.2 NA by iteratively optimizing the total intensity of the synthetic aperture images in the forward and phase-conjugation processes. At a source wavelength of 785 nm, we demonstrated a spatial resolution of 372 nm at extremely long working distances of up to 1.6 mm, an order of magnitude improvement in comparison to conventional objective lenses. Our method of converting microscope condensers to high-quality objectives may facilitate increases in the imaging depths of super-resolution and expansion microscopes.
Highlights
The performance of an optical microscope is often characterized by its spatial resolving power
We recently developed an aberration correction approach employing indirect wavefront sensing methods called closed-loop accumulation of single scattering (CLASS) microscopy working in the reflection geometry[38]
A pair of commercial microscope condensers turned into diffraction-limited objectives with an order-of-magnitude longer working distance than the conventional oil-immersion objective lenses
Summary
We constructed a transmission-mode coherent imaging system based on a Mach-Zehnder interferometer (Fig. 1). Note that if the optics are free from aberration a→nd uncontrolled drift, the angular spectrum of the synthetic aperture image will be proportional to (∆ k ). The system aberration has two major detrimental effects on the synthetic aperture image: the absolute value of the cross-correlation becomes smaller, which causes a reduction in si→gnal intensity, and the phase value of the cross-correlation becomes dependent on the momentum difference ∆ k. This distorts the PSF of the optical system, thereby distorting the target structure in the reconstructed image. The accumulation of the correction functions converged to its corresponding aberration maps, i.e. ∑nθi(n) → φi + g , and ∑nθo(n) → φo
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