Abstract

Optical coherence tomography (OCT) is a well-established non-contact and non-invasive method for three-dimensional structural imaging of complex samples [1]. This technique is actively used for various biomedical applications, such as medical diagnosis. However, the relatively shallow penetration depth is considered a serious limitation for many applications. Optical time-of-flight (TOF) measurements provide an alternative way to acquire three-dimensional structural images. A temporal resolution of 150 femtoseconds corresponding to the axial resolution comparable to OCT has been reported [2]. The penetration depth would be enhanced by using the wavelength in the spectral window of 1550 – 1800 nm, because the scattering and absorption losses can be reduced. Besides them, the phenomenon of multiple scattering also makes it difficult to achieve meaningful structural information at deeper penetration depths. To enhance image contrast at larger penetration depths, multiply scattered photons must be removed. Although they overlap in both spectral and time domain with the singly reflected signal photons, they would be removed by the mode-selective up-conversion single-photon detector (UCSPD) [3,4]. We report on the optical TOF measurement system using the time-resolved and mode-selective UCSPD and its application to the tomographic image acquisition of a mouse brain.

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