Comparative discrimination spectral detection method for the identification of vapors using overlapping broad spectral filters.

We present a comparative discrimination spectral detection approach for the identification of chemical vapors using broad spectral filters. We applied the method to flowing vapors of as-received and non-interacting mixtures for the detection of the volatile components of a target chemical in the presence of interferents. The method is based on measurements of the overall spectral signature of the vapors, where the interferent spectrum largely overlaps the target spectrum. In this work we outline the construction of a set of abstract configuration-space vectors, generated by the broadband spectral components from sampled chemical vapors, and the subsequent vector-space operations between them, which enable the detection of a target chemical by comparative discrimination from interferents. The method was applied to the C-H vibrational band from 2500 to 3500 cm(-1), where there is large spectral signal overlap between the chosen target chemical and two interferents. Our results show clear detection and distinction of the target vapors without ambiguity.

10% Yb3+-Lu2O3 ceramic laser with 74% efficiency.

We demonstrate laser oscillation at 1080 nm with more than 16 W of output power and with an optical-to-optical slope efficiency of up to 74% using a 10% Yb3+ doped Lu2O3 ceramic made by hot pressing. This represents the highest output power and efficiency obtained for a Yb3+ doped Lu2O3 ceramic and demonstrates the feasibility for power scaling.

Delivery of midinfrared (6 to 7-microm) laser radiation in a liquid environment using infrared-transmitting optical fibers.

Ablation at wavelengths near lambda = 6.45 microm results in tissue ablation with minimal collateral damage (< 40 microm) yet yields a high ablation rate that is useful for human surgery. However, delivery of this wavelength has been limited to that in air and thus to applications in which the target tissue can be readily exposed. The goal of this study is to investigate the potential of a pulsed infrared laser at lambda = 6.45 microm for noncontact ablation in a liquid environment. To this end we investigated fiber delivery in combination with the use of infrared transparent liquids. Transmission characteristics and damage thresholds for two types of fiber materials (silver halide and arsenic sulfide), for high-power pulsed laser radiation were determined using the Mark III free electron laser. Both fibers had comparable bulk losses (0.54 dB/m and 0.62 dB/m, respectively) while the arsenic sulfide fibers showed more coupling losses (37 versus 27%). Damage thresholds were higher in arsenic sulfide fibers than in silver halide fibers (1.12 GW/cm2 versus 0.54 GW/cm2), but both fibers were sufficient to deliver radiant exposures well above the ablation threshold in tissue. Seven different perfluorocarbon liquids (PFCLs), known for their transparency at lambda = 2.94 microm, were investigated and their optical transmission was determined using Fourier transform infrared and direct Beer's law measurements. All of the PFCLs tested had similar values for an absorption coefficient mu(a) at a given wavelength (mu(a) = 0.05 mm(-1) at lambda = 2.94 microm and mu(a) is approximately 3 mm(-1) at lambda = 6.45 microm). Pump-probe imaging showed the ablation sequence (lambda = 6.45 microm) at the fiber tip in a water environment, which revealed a fast expanding and collapsing bubble. In contrast, the volatile PF-5060 showed no fast bubble expansion and collapse, but rather formation of nontransient gas bubbles. Perfluorodecalin did not show any bubble formation at the radiant exposures used. It was shown that using the lambda = 6.45 microm wavelength delivered via fiber optics in combination with perfluorodecalin allows a noncontact laser surgical procedure. Deeper structures, however, are effectively shielded because the radiant exposure of the beam will fall below the ablation threshold owing to the absorption by perfluorodecalin. This may optimize the efficacy and safety of laser-based vitreoretinal surgery.

Chemically resolved imaging of biological cells and thin films by infrared scanning near-field optical microscopy.

The infrared (IR) absorption of a biological system can potentially report on fundamentally important microchemical properties. For example, molecular IR profiles are known to change during increases in metabolic flux, protein phosphorylation, or proteolytic cleavage. However, practical implementation of intracellular IR imaging has been problematic because the diffraction limit of conventional infrared microscopy results in low spatial resolution. We have overcome this limitation by using an IR spectroscopic version of scanning near-field optical microscopy (SNOM), in conjunction with a tunable free-electron laser source. The results presented here clearly reveal different chemical constituents in thin films and biological cells. The space distribution of specific chemical species was obtained by taking SNOM images at IR wavelengths (lambda) corresponding to stretch absorption bands of common biochemical bonds, such as the amide bond. In our SNOM implementation, this chemical sensitivity is combined with a lateral resolution of 0.1 micro m ( approximately lambda/70), well below the diffraction limit of standard infrared microscopy. The potential applications of this approach touch virtually every aspect of the life sciences and medical research, as well as problems in materials science, chemistry, physics, and environmental research.