We have measured the mid-infrared spectra of several tissues in a malignant and normal state, using the ATR sampling method. The aim of the experiments was to detect cancer signatures that were discovered earlier using other sampling methods. The ATR method is particularly attractive for medical applications because it can be used in-vivo, and because it requires minimal sample preparation. We have succeeded to detect a significant signature in only one of the five spectral bands that were examined. This signature is attributed to the PO2- symmetric stretching of the nucleic acids phosphodiester groups, and is located in the vicinity of 1082 cm-1. The signature consists of a shift in the maximum absorption peak by 3 cm-1. The measured data is in good agreement with the published data. This result can lead to real-time tumor mapping during surgery and in-vivo cancer diagnosis with fiber-optic ATR probes.
The optical power distribution along step index As2Se3 chalcogenide-glass multimode fibers in the mid IR region was studied experimentally. The experimental set-up consists of an Ir source with collimating and focusing optics, and step index As2Se3 multimode fibers in different lengths. The far field radiation intensity of the fiber was obtained by moving an MCT detector with different band pass filters on an arc centered at the fiber exit.
Construction and characterization of the first multimode fiber couplers in the mid-IR region (2 to 10 μm) are reported. These couplers are made of step-index As2Se3 chalcogenide glass fibers whose cores were brought to a contact along a certain distance. Far-field measurements using selective angular excitation indicated a typical coupling ratio of 15% (8.2 dB) from couplers made of 550-μm core diameter fibers with a 10-cm interaction length. The excess insertion loss was less than 0.2 dB. Strong mode mixing caused by the coupling mechanism is observed, resulting in a significant broadening of the radiation distribution.
The far-field patterns of two types of nonimaging concentrators were studied experimentally both in the visible and in the infrared. The input beam was a diffuse light generated by a black-body source, with a well-defined divergence angle. Several new features were observed, and were explained with a simple model based on geometrical optics.
Optical coherent LIDARs are used for remote sensing in both atmospheric and space environments. These systems offer higher angular resolution with significantly more compact components as compared to the alternative microwave-based systems. One of the factors which limits the range of coherent LIDARs is the coherence length of the source. It is well known that the signal in a coherent LIDAR system undergoes a significant decay over a range comparable to the source coherence length. An often overlooked fact is the range-associated increase of the optical noise. In this paper we present the spectral power density of the optical noise in a heterodyne LIDAR system, and explore its dependence on the range and the local oscillator power. The magnitude of the optical noise increases with range, thus accelerating the signal-to-noise degradation. Another interesting observation is that in general, the signal- to-noise ratio is not a monotonically increasing function of the local oscillator power.
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