Up-converters

The materials used as up-converters consist of a rigid host lattice with rare earth dopants. Fluorides and oxides have been used as host lattices, the latter being slightly 

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A modern variation on the rapid scan spectrometer, which is under development, uses a laser-generated plasma as a high intensity broad-band IR source (65). This method has been used to probe the vc—o absorption of W(CO)6. Another technique TRISP (time-resolved IR spectral photography), which involves up-conversion of IR radiation to the visible, has also been used to probe transients (66). This method has the enormous advantage that efficient phototubes and photodiodes can be used as detectors. However, it is a technically challenging procedure with limitations on the frequency range which depend on the optical material used as an up-converter. 

Possible future applications of up-converting phosphors include (i) three-dimensional displays 249-251 (ii) fiber optic amplifiers (referred to above) that operate at 1.55, 1.46, and 1.31 pm,, 2 1-255 (iii) up-conversion lasers 250 and (iv) remote sensing thermometers for high-temperature applications (utilizing the temperature dependence of optical properties of, for example, cubic Y203 Er3+).256-258... 

January 2001 I used the virtual bench design tool to verily my comp selection for 12V to 23V at 500mA step-up converter using the 2577. The virtual bench tool came back with a much smaller inductor (68uH) than the charts and equations in the datasheet seem to indicate. What s the deal ... 

Currently used nonlinear optical crystals are potassium dihydrogen phosphate (KDP) and barium borate (BBO). Compared to KDP, the advantages of BBO are its transparency in the UV and its larger quantum efficiency of up-conversion by a factor of 4—6. For a given position of the crystal, only a narrow band of the fluorescence spectrum is up-converted. Therefore, if the full fluorescence spectrum is of interest, the crystal must be rotated at a series of angles. An example of experimental set-up is presented in Figure 11.2. The fwhm of the response is 210 fs. 

Let N(j,Ni,N2, and Nj, be the equilibrium population densities of the states 0, 1,2, and 3, respectively (reached under continuous wave excitation intensity Iq), and let N = NQ + Ni+N2 + N3he the total density of optical absorbing centers. The up-converted luminescence intensity ho (corresponding to the transition 2 0) depends on both N2 and on the radiative emission probability of level 2, A2. This magnitude, which is dehned below, is proportional to the cross section a20 (called the emission cross section and equal to the absorption cross section ao2, as shown in Chapter 5). Thus we can write... 

Up-converters are materials that absorb infrared radiation and convert this into visible wavelengths. 

FIGURE 3.4 Performance of the fluorescence up-conversion microscope, (a) Evaluation of the time-resolution with the 100 x objective lens , up-converted fluorescence -F-, the first derivative. By the fitting analysis, the time-resolution of the microscope was evaluated as 520 fs. (b) Evaluation of the transverse (XY) spatial resolution with the 100 x objective lens. A CCD image of the excitation pulses (inset) and the beam profile along the lateral (X) direction. By the fitting analysis, the transverse resolution was evaluated as 0.34 pm. (c d) Evaluation of the axial (Z) spatial resolution with the 100 x objective lens , up-converted fluorescence -I-, the first derivative. By fitting analysis on the first derivative coefficient, the axial resolution was evaluated as 1.1 pm with the 50 pm pinhole (c) and 5.3 pm without pinhole (d). (Rhodamine B, 2 x 10" mol dm in methanol, 600 nm.) (Erom Eujino, T. and Tahara, T., Appl Phys. B 79 145-151, 2004. Used with permission.)... 

Two-photon excitation can be used for the fluorescence up-conversion microscope, and high axial resolution was achieved without a pinhole in this case. Figure 3.5 shows the up-converted fluorescence from a coumarin 522B solution at a fluorescence wavelength of 520 nm observed in the same manner of Figure 3.4d without pinhole. In this measurement, a fundamental laser pulse at 800 nm was used for excitation. The axial resolution with two-photon excitation was evaluated to be 0.97 pm (FWHM) by fitting for the first derivative of the obtained data. This result indicates... 

The flnorescence dynamics imaging was carried ont by monitoring time-resolved fluorescence at 530 nm, where the rise of the tetracene fluorescence is observed, at different positions of the microcrystal. The np-converted fluorescence data were recorded every 1 pm distance. To shorten the measnrement time at each point, the up-converted signal was sampled at only fonr delay time points (- 5, 5,15, 30 ps), and then the energy transfer time, x, was evalnated by htting with the following single-exponential fnnction ... 

Fig. 28 a Single-photon fluorescence readout of data recorded by single-photon writing scale bar 100 ixm) b intensity profile (the direction is shown hy the arrows) of (a) c two-photon fluorescence readout of data recorded by single-photon writing (scale bar 100 xm) d intensity profile (the direction is shown by the arrows) of (c) e quadratic dependence of up-converted fluorescence of fluorene 17 on the input intensity. The smallest readout pattern achieved in this system was 3.5 xm... 

Fig. 30 Two-photon fluorescence image of storage medium before (a) and after (b) two-photon recording, c DIG readout of the storage data after two-photon recording, and d input intensity dependent up-converted fluorescence of fluorene 17...

Here, fwo enhancement effects are present (i) the incident laser field is enhanced in the nanoparticle according to Eq. 19, and (ii) the up-converted field component is also enhanced. The SHG enhancement factors from nanostructured Ag as high as 10 (compared to that from atomically flat Ag surface) were observed even for the forbidden case of s-polarized pump beam [61]). This enhancement can be utilized for faciUtating TPA and MPA processes. 

The possibility of cis-trans equilibria exists, but has not been explored in depth. One indication for such equilibria comes from the NMR investigation of the parent nickel dithiolene in a nematic solvent only a rapidly equilibrating compound could have produced the observed spectral pattern.35 In the preparation of some mesomorphic dithiolenes related to the one cited above, two products were initially obtained, which during further work-up converted into the trans isomer only.38 In Pt complexes of this type, the existence of two 195Pt- H couplings was taken as an indication36 that the cis and trans isomers coexisted. 

For second harmonic generation (SHG), the tensor is y(2)(—2co co, co) (useful for frequency doubling and parametric down-conversion) while for the linear electrooptic or Pockels71 effect the tensor is y(2)(— co co, 0) (useful for Q-switching of lasers, for phase or amplitude modulators, and for beam deflectors) for optical rectification the tensor is y 2>(0 00, —co) for frequency mixing the tensor is y(2)(— co3 oolr co2) (useful for frequency up-converters, optical parametric oscillators, and spectroscopy). 

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