Cryogenic mirror position actuator for spectroscopic applications.

We demonstrate a mirror position actuator that operates in a wide temperature range from room temperature to a deep cryogenic regime (10 K). We use a Michelson interferometer to measure the actuator tuning range (and piezoelectric efficiency) in the full temperature range. We demonstrate an unprecedented range of tunability of the mirror position in the cryogenic regime (over 22 µm at 10 K). The capability of controlling the mirror position in the range from few to few tens of microns is crucial for cavity-enhanced molecular spectroscopy techniques, especially in the important mid-infrared spectral regime where the length of an optical cavity has to be tunable in a range larger than the laser wavelength. The piezoelectric actuator offering this range of tunability in the cryogenic conditions, on the one hand, will enable development of optical cavities operating at low temperatures that are crucial for spectroscopy of large molecules whose dense spectra are difficult to resolve at room temperature. On the other hand, this will enable us to increase the accuracy of the measurement of simple molecules aimed at fundamental studies.

Quantitative measurements of formalin-induced fluorescence for differential diagnostics of melanomas and lesions of human skin.

The usefulness of formaldehyde-induced fluorescence (FIF) for detection of melanoma cells has been suggested by several investigators during the last 40 years. FIF can be easily excited and observed in microscopic sections of formalin-fixed paraffin-embedded skin samples. However, such an approach has never been widely used in melanoma diagnostics for reasons including lack of clear diagnostic criteria, considerable inconsistencies in both the protocols used and qualitatively analysed results reported by different groups. This study aimed at determination of the spectral bands optimum for detecting melanoma cells. The study involved three sets of the excitation and emission bands: gammaex=366 nm, gammaem>425 nm; gammaex=450-480 nm, gammaem>515 nm; gammaex=450-480 nm, gammaem=510-550 nm. Microscopic digital imaging was used to quantitatively determine the fluorescence intensity of 53 primary melanomas and 32 benign lesions. Best classification of melanomas with algorithm based on fluorescence intensity threshold was obtained for gammaex=450-480 nm, gammaem=510-550 nm. Receiver operating characteristics (ROC) analysis of the algorithm yielded area under the curve=0.84 +/- 0.05 for melanocytic cells present in the stratum corneum. Our results clearly indicate that the FIF emitting molecules (most probably 5-S-cysteinyldopa) are present in melanomas at the concentration significantly higher than in benign lesions. In terms of the ROC analysis, the diagnostic performance of the test based on the FIF intensity is as good as of many other commonly used diagnostic tests.

Variability of spectra of laser-induced fluorescence of colonic mucosa: its significance for fluorescence detection of colonic neoplasia.

To determine the extent of a natural variability of the spectra of the autofluorescence and its significance for a reproducibility of different approaches typically used in studies on fluorescence detection of colonic lesions. Two independent series of experiments have been conducted during three years in the same laboratory. Macroscopic tissue specimens obtained during operations of patients with colonic cancers were studied in vitro. The tissues were excited using UV lines of c.w. He-Cd laser and pulsed nitrogen laser and the autofluorescence spectra were recorded for areas visually diagnosed as normal or pathologically changed mucosa. Natural variability of the autofluorescence spectra of colonic tissues seems to be most important factor limiting sensitivity and specificity of the diagnostic algorithms. The mean fluorescence spectra obtained for normal mucosa and its neoplastic lesions differ significantly but the differences are difficult to observe because of the high natural variability among the individual spectra. Further studies of biological basis of the colonic autofluorescence are necessary for a progress in the field of fluorescence detection of colonic neoplastic lesions.