Real-time spectral imaging in three spatial dimensions

Abstract

We report what is to our knowledge the first volume-holographic optical imaging instrument with the capability to return three-dimensional spatial as well as spectral information about semitranslucent microscopic objects in a single measurement. The four-dimensional volume-holographic microscope is characterized theoretically and experimentally by use of f luorescent microspheres as objects. © 2002 Optical Society of America OCIS codes: 090.2890, 110.0110, 090.1970 Classical imaging systems process the optical f ield by use of elements such as lenses, apertures and stops, and thin diffraction gratings. By placing several such elements in tandem, one can capture projections of very general objects, e.g., containing three-dimensional (3D) spatial as well as spectral information. We refer to such objects as four dimensional (4D). The projections that these systems are capable of forming are twodimensional (2D) or lower; scanning is needed to span the entire 3D or 4D object space. For example, a classical confocal microscope 1 -3 uses a combination of objective -collector lenses and a pinhole to capture information about a single point in the object and acquires a zero-dimensional projection at every measurement. Scanning along three dimensions is needed to acquire the 3D spatial structure of the object. By providing spectral scanning means (e.g., a monochromator or a scanning Fabry -Perot interferometer), one can also acquire spectral information, albeit in a very time-consuming procedure. Optical coherence tomography 4 requires only 3D scanning for capturing spatial information, whereas spectral information is recovered digitally from the phase of the correlation function of the optical beam. 5Coherence imaging 6 -9 returns 2D projections in the Fourier ͑k͒ space at the expense of dynamic range. Here we report what is, to our knowledge, the first instrument with the capability to acquire spatial and spectral information simultaneously (in a single measurement). Therefore, real-time 4D imaging becomes possible at rates specified by the photon count and not the scanning speed.The 4D imaging capability is based on the Bragg diffraction selectivity and degeneracy properties of volume holograms. -12The principle of volume-holographic imaging is illustrated in Fig. 1. The optical field emitted or scattered by a 4D object is transformed by the appropriate combination of lenses and subsequently diffracted by a volume-holographic optical element, which has been prerecorded to multiple superimposed holograms. Each hologram is tuned to its corresponding 2D slice of the 4D object. If the projected slices span the entire 4D object space, then the need for scanning is eliminated.In this Letter we discuss and experimentally characterize a specif ic holographic imaging of transmission geometry. With the detailed structure shown in Fig. 2, the hologram is recorded by interfering the signal beam, collimated from a monochromatic coherent point source at ͑x r , y r , z r

Imaging using volume holograms

“…The bandwidth of the fluorescent light results in an increased field of view ͑FOV͒ with accompanying degradation of depth resolution. 31,32 In this case, it is beneficial to reconcile the three VHI images using a least-squares optimization to obtain the actual 3-D intensity distribution of the object. The experimental results are shown in Fig.…”

Coherent Optical Information Systems

“…Holographic, or more generally interferometric, techniques have found interesting applications in imaging other than 3D displays (8,9). Because interferometric detection preserves the phase of the field, it is possible to extract more information about the object being imaged than can be done with conventional techniques.…”

Wigner analysis of three dimensional pupil with finite lateral aperture

“…The use of volume holographic (VH) pupils in imaging systems includes applications such as hyper-spectral image acquisition [1], profilometric imagers [2,3], unhindered imaging capability under broadband illumination, and multi-focal microscopic imaging [4,5]. Compared to conventional 2D imaging pupils such as thin gratings and lenses, the VH pupil at a 4-f imagers' Fourier plane acts as a 3D optical element, providing unique opportunities to process the optical field in three spatial dimensions as well as wavelength [6,7].…”