Real-time, auto-focusing digital holographic microscope using graphics processors

Abstract

The most significant advantage of holographic imaging is that one does not need to do focusing alignment for the scene or objects while capturing their images. To focus on a particular object recorded in a digital hologram, a post-processing on the recorded image must be performed. This post-processing, so called the reconstruction, is essentially the calculation of wave propagation in free space. If the object's optical distance to the recording plane is not known a priori, focusing methods are used to estimate this distance. However, these operations can be quite time consuming as the hologram sizes increase. When there is a time constraint on these procedures and the image resolution is high, traditional central processing units (CPUs) can no longer satisfy the desired reconstruction speeds. Then, especially for real-time operations, additional hardware accelerators are required for reconstructing high resolution holograms. To this extend, today's commercial graphic cards offer a viable solution, as the holograms can be reconstructed tens of times faster with a graphics processing unit than with the state-of-the-art CPUs. Here we present an auto-focusing megapixel-resolution digital holographic microscope (DHM) that uses a graphics processing unit (GPU) as the calculation engine. The computational power of the GPU allows the DHM to work in real-time such that the reconstruction distance is estimated unsupervised, and the post-processing of the holograms are made completely transparent to the user. We compare DHM with GPU and CPU and present experimental results showing a maximum of 70 focused reconstructions per second (frps) with 1024 × 1024 pixel holograms.

Improving Phase Contrast of Digital Holographic Microscope using Spatial Light Modulator

“…This function represents the point-spread function of phase contrast microscope: (12) Similarly, in the annulus SLM position, we have an even number of phases with n band rings, which have opposite phases. For example, the first band ring has phase ϕ , the second band ring has phase -ϕ , and so on.…”

“…Furthermore, the focus adjustment can be carried out numerically after the measurement, and mechanical auto focus tracking during the measurement is avoided. Thus, DHM offers the advantage of multiple focus plane reconstruction from a single hologram [12]. However, when a thick specimen is used as an object, the images are often surrounded by bright areas, which obscure details along the perimeter of the specimen.…”

“…The DHM provides quantitative phase contrast imaging suitable for high-resolution investigations on reflective surfaces as well as for markerfree analysis of living cells [11,12]. Furthermore, the focus adjustment can be carried out numerically after the measurement, and mechanical auto focus tracking during the measurement is avoided.…”

Autofocus method for automated microscopy using embedded GPUs

“…In [8] authors applied desktop GPU board to digital holographic microscopy (DHM) obtaining 24 frames reconstructed per second (frps) with resolution of 512x512. Dogar et al [9], improved that result up to 70frps (1024x1024 resolution) employing a 1334-core GPU. Similarly, Kang et al [13] employed a GPU populated with 2880 cores for real-time volumetric display of optical-resolution photoacoustic microscopy (OR-MAP).…”

Video-rate computational heterodyne holography

“…Computational rendering techniques of optical holograms on GPUs [9,10] have led to real-time qualitative holographic vibration imaging of nanometric out-of-plane vibrations at narrow [11] and wider [12] detection bandwidths. GPU image rendering has enabled fast auto-focusing of megapixel-resolution holograms [13], speckle diversity rendering [14], three-dimensional microscopic scenes rendering [15][16][17][18][19][20]. For time-consuming holographic image rendering, in particular when real-time performance is required, hardware acceleration of computations should be considered [21,22].…”