Single channel in-line multimodal digital holography Academic Article uri icon

abstract

  • We present a new single channel in-line setup for holographic recording that can properly record various objects that cannot be recorded by the Gabor holographic method. This configuration allows the recording of holograms based on several modalities while addressing important issues of the original Gabor setup, including the well-known twin-image problem and the weak scattering condition. © 2013 Optical Society of America OCIS codes: (090.0090) Holography; (090.1995) Digital holography; (110.6880) Three-dimensional image acquisition; (100.3010) Image reconstruction techniques; (070.6120) Spatial light modulators. http://dx.doi.org/10.1364/OL.38.004719 Digital holography concerns the recording of a hologram using a solid-state detector array and the numerical reconstruction of the recorded object, or scene. Using a computer, the reconstruction is achieved via the decod-ing of the recorded hologram. Many methods of digital holography have been proposed throughout the years [1]. However, since the introduction of holography by Gabor [2], a single channel configuration has remained the most appealing type of hologram recording setup. In a single channel (in-line) holographic setup, the object and all other components are positioned on the same optical axis, enabling the use of low spatial and temporal coherence illumination sources and reduced stability requirements (see, e.g., [3]). Furthermore, maximal space-bandwidth-product can potentially be achieved [4]. In this Letter, we propose a new, to the best of our knowledge, single channel interferometer for the recording of digital holograms. This configuration can be described using the original Gabor holographic configu-ration [2]. Gabor originally described an in-line configu-ration, where the interference occurs between two wavefronts: one, scattered by the object, and another, which is unscattered. This principle imposes several re-strictions on the object, such as the weak scattering con-dition. Under this condition, a large enough portion of the light must be unscattered upon passing through the ob-ject, so that it can be used as a reference wavefront; thus, making the Gabor setup impractical for dense samples. Another element that sets limits on the performance of the original Gabor holography is the twin image term, evi-dent in the reconstruction. Throughout the years, several techniques have been proposed to remedy these prob-lems. For example, computational techniques were sug-gested to remove the twin image [5] and bias terms [6]. Other methods have implemented optical and digital means that together perform an in-line phase-shifting technique. This was demonstrated for both incoherent [3,7] and coherent systems [8]. We propose a method by which the in-line hologram is formed through an interference of object scattered wave-front and unscattered wavefront, in a similar fashion to the original Gabor holography. However, the proposed method is superior to the Gabor working principle in the following manners: (1) Control over the reference field to object field intensity ratio is offered; that is, this ratio is no longer simply object dependent, remedying the weak scattering condition; (2) The complex field amplitude of the object can be extracted, either from a phase-shifting holography experiment or from a single shot, in the same manner as in off-axis holography. The twin-image problem is thus addressed; (3) The method allows the recording of Fresnel, image and (potentially) Fourier holograms, with only minor modifi-cations to the setup, some of which are digitally set, with-out any mechanical movement of the equipment; and (4) The setup potentially can be used to perform on-axis reflection holography. A schematic sketch of the recording setup is shown in Fig. 1. The setup contains two polarization dependent spatial light modulators (SLMs) located between two, in parallel polarizers, and a digital camera. The SLMs are placed with their active axes perpendicular to each other and at a 45° angle to the transmission axis of the two polarizers. The second polarizer is used to isolate, from the two orthogonal polarizations, two polarization components that have the same polarization direction and can, therefore, interfere [9]. As the input object is illuminated with a collimated laser beam, each SLM only phase-modulates components of the incident light

publication date

  • January 1, 2013