We present an optical imaging system, called "optical echography", which provides longitudinal slices of a biological sample directly and at video-rate. The apparatus, based on a femtosecond laser light source, employs the property of time-to-space conversion of a single-shot correlator in order to image in vivo biological tissues with a depth resolution of 10 micrometers.
We propose a new technique for caries imaging by the spectral analysis of teeth luminescence excited by the near UV light. This diagnostic/control method can be applied for the all optically accessible teeth surfaces. The photo-physical studies suggest that hydroxylapatite luminescence, excited in the near UV, comes from de-excitation of crystalline structure defects in interaction with charge donating/accepting en ironment.
In this communication, we propose a non-invasive imaging setup which does not require any lateral and longitudinal scanning over the sample. The idea is to image a line over the sample surface with a laser and to collect the photons backscattered by the sample surface and the internal structures. As a result, a single shot 2D image of the sample can be obtained, one axis representing a lateral coordinate and the other one the longitudinal coordinate, e.g. the depth of the sample. To collect the backscattered light from the sample, we use a femtosecond laser source and the potential of a classical single-shot autocorrelator to make a time-to-space conversion by use of non-collinear sum frequency generation in a nonlinear crystal. With this technique, we performed single shot longitudinal imaging of an ex vivo mouse ear and in vivo human skin with a 35 micrometers lateral and 15 micrometers depth resolution in tissues. Inside the mouse ear, the epidermis, dermis and cartilage have been observed. In the in vivo human skin, the stratum corneum, the epidermis and the dermis have been observed. Especially, the epidermal-dermal junction has been clearly revealed and the thickness of the epidermis has been measured.
A two-dimensional optical coherence tomography technique has been developed in order to obtain multiple longitudinal slices of a biological sample directly, in a single Z-scan. The system is based on a femtosecond Cr4+:Forsterite laser and an infrared camera for wide-field imaging of the sample with a depth resolution of 9 micrometers . With this imaging apparatus, we investigated biological tissues such as human skin, human tooth and a mouse ear to observe the different constitutive tissues of the samples.
Optical Kerr gate with a function of light amplification and a femtosecond opening time in a special fast setup is applied to time-resolved imaging. Transient induced anisotropy created by a first pump pulse is canceled by the perpendicular-induced anisotropy which is created by a delayed pump. The transverse resolution of the image is better than 90 micrometers without degradation originated from optical Kerr effect or optical amplification process. Moreover, rather wide spectral band of the gate offers the possibility of spectroscopic imaging. 3D imaging of small- signal objects using the femtosecond amplifying optic al Kerr gate are demonstrated for several types of transmittance objects hidden behind light diffusers.