Laser induced fluorescence microscope

Here we present the latest results from our group focused on the design of tailored femtosecond pulses to achieve control of nonlinear optical excitation in large molecules based on the concept of multiphoton intrapulse interference (Mil) [1-4]. Our goal is to elucidate well-defined and reproducible pulse shapes that can be used to enhance or suppress particular nonlinear optical transitions in large molecules such as laser dyes and proteins in solution. We demonstrate the use of Mil to probe the local and microscopic environment of molecules by selective two-photon laser induced fluorescence (LIF). 

FIGURE 7.1 Schematic of the laser-induced fluorescence detection system. Excitation was provided by an argon ion laser light. It was focused with a lens (1) onto the separation channel in a microchip. The chip was held in place with a Plexiglas holder (2). Fluorescence emission (3) was collected with a microscope objective (4), focused onto a spatial filter (5), emission filter (6), and then detected with a photomultiplier tube [550]. Reprinted with permission from the American Chemical Society. 

Jiang, G., Attiya, S., Ocvirk, G., Lee, W.E., Harrison, D.J., Red diode laser induced fluorescence detection with a confocal microscope on a microchip for capillary electrophoresis. Biosens. Bioelectronics 2000, 14, 861-869. 

CLM method can also be combined with various kinds of spectroscopic methods. Fluorescence lifetime of an interfacially adsorbed zinc-tetra-phenylporphyrin complex was observed by a nanosecond time-resolved laser induced fluorescence method [25]. Microscopic resonance Raman spectrometry was also combined with the CLM. This combination was highly advantageous to measure the concentration profile at the interface and a bulk phase [14]. Furthermore, circular dichroic spectra of the liquid-liquid interface in the CLM could be measured [19]. 

If the molecule stays for a time T within the laser beam which is long compared to the lifetime t of the upper laser-excited state (fc the molecule can undergo n = r/(2r) absorption-emission cycles. The laser-induced fluorescence is observed through a microscope. 

Laser-Induced Fluorescence, Fig. 4 (a) Sketch of STED fluorescence microscope, (b) The detection spot of STED fluorescence microscope and the light intensity of the detection spot... 

In the present article we give an overview of recent work carried out in our laboratory in order to study microscopic details of bimolecular gas phase reactions at the molecular level using the laser photolysis / laser-induced fluorescence (LP/LIF) pump-and-probe technique. In particular, we will focus on the following three- and four-atom reactions ... 

Fig. 84 Comparison of fluorescence and optical microscopic images of poly(butyl methacrylate) PBMA (a) and (c), and poly(ethyl methacrylate) PEMA (b) and (d) target polymer sin-face following 355-nm laser-induced molecular transfer of pyrene contained in triazene polymer. Irradiation dose 5 pulses, 200 mj cm-2. The bar denotes 100 jltm in each case. REPRINTED WITH PERMISSION OF [Ref. 360], COPYRIGHT (1998) Elsevier Science...

Besides total concentration of multielements, their spatial distribution in samples is also very important in understanding their bioavailability, trophic transfer, and environmental risk. A number of complementary analytical techniques exist for the mapping of elemental distributions in biological tissues including SRXRF (synchrotron radiation X-ray fluorescence) with microbeam (SR-pXRF), microscopic EDX (energy-dispersive X-ray fluorescence), microscopic WDX (wavelength-dispersive X-ray fluorescence), microscopic PIXE (particle-induced X-ray emission), laser ablation ICP-MS, microscopic SIMS (secondary ion mass spectrometry). 

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