Laser polychromator

Nanosecond pump probc time-resolved resonance Raman experiments were carried out with two Nd YAG lasers (At=7 ns) which provide the pump- (532 nm, 4 mJ) and probe pulses (416 nm, 100 mJ), a triple polychromator equipped with an intensified photodiode array, and a slow spinning cell (25tpm). For every sample, spectra were taken for delay times of At=-20, 0, 20,100 and 500 ns, 1,10,100 and 500 is, and 1ms. ... 

Figure 5.3 shows a schematic illustration of our HRS measurement system [26-28]. A mode-locked Ti sapphire laser (Spectra-Physics, Tsunami) was used to induce HRS. Pulses of 70 fs at 790 nm with a repetition rate of 82 MHz were spectrally narrowed by a custom-made laser line filter (Optical Coatings Japan). The obtained pulse width was 14 cm FWHM with a pulse duration of 1 ps (measured by autocorrelation). These pulses were introduced into an inverted microscope system (Nikon, TE-2000) with a 36x, 0.52 N.A. reflective microscope objective or a 100 X, 1.49 N.A. oil-immersion microscope objective. Backscattered photons were collected by the same objective and filtered by dichroic mirrors (Optical Coatings Japan). Finally, HRS signals were detected by a charge-coupled camera (Princeton Instruments, PIXIS 400B) with a polychromator (ACTON, SP2500i). 

A line-scan of the illumination laser light has been used to enhance the scan rate, at least compared to the point-by-point scan [18, 21-25]. It remains compatible with a spectral acquisition of high resolution, since total fluorescence from the linear region can be projected onto the slit of an imaging polychromator. A CCD camera at the exit port records the fluorescence intensity as a function of the spatial coordinate and the wavelength in the two-dimensional sensitive area of the camera. This method... 

A few reports have appeared on combining the streak camera temporal dispersion with polychromators and three dimensional optical multichannel detection. This approach yields three dimensional fluorescence data for each laser pulse. With the present technological limitations of three dimensional detectors and streak cameras, however, data of this type suffer from low wavelength resolution. As detector and streak camera technology improve, this technique may become the method of choice for time and wavelength resolved emission spectra. 

Often a long-pass filter must be inserted in the polychromator to improve the blocking of scattered laser light. The spechnm at the output of the polychromator is detected by a multianode PMT, and the decay curves in the spectral channels are recorded by multidetector TCSPC. 

Dual-wavelength TCSPC detection in two-photon laser scanning microscopes is relatively simple [37]. Multispectral TCSPC detection in a two-photon laser scanning microscope requires a suitable relay optics between the objective lens and the polychromator [35, 60]. Details are described under TCSPC Laser Scanning Microscopy . 

Often a broadband laser (for example, a pulsed dye laser without etalons), or a multiline laser (for example, a CO2 or CO laser without grating) may simultaneously cover several absorption lines of different molecules. In such cases the reflected beam is sent to a polychromator with a diode array or an optical multichannel analyzer (OMA, Vol. 1, Sect. 4.5). If a fraction of the laser power Po(< ) is imaged onto the upper part of the OMA detector and the transmitted power onto the lower part (insert in Fig. 10.17), electronic difference and ratio recording allows the simultaneous determination of the concentrations V/ of all absorbing species. A retroreflector arrangement is feasible for measurements at low altitudes above ground, where buildings or chimneys can support the construction. Examples are measurements of fluorine concentrations in an aluminum plant [1452], or the detection of different constituents in the chimney emission of power plants, such as NOjc and SOj components [1453]. Often, ammonia is added to the exhaust of power stations in order to reduce the amount of NO emission. In such cases, the optimum... 

Vaughn, K.I, Conlee, C.A., Neff, H., Schreiber, K.J. (2005) A compositional analysis of Nasca polychrome paints implications for craft production on the pre-Hispanic south coast of Peru. In Laser Ablation ICP-MS in Archaeological Research, edited by Speakman, R.J., Neff) H. Albuquerque, NM University of New Mexico Press, pp. 138-154. 

Often a broadband laser (for example, a pulsed dye laser without etalons), or a multiline laser (for example, a CO2 or CO laser without grating) may simultaneously cover several absorption lines of different molecules. In such cases the reflected beam is sent to a polychromator with a diode array or an optical multichannel analyzer (OMA, Sect. 4.5). If a fraction of the laser power Po(co) is imaged onto the upper part of the OMA detector and the... 

Figure 4.74 Output signals at the polychromator and the three diode arrays of the FPI wavemeter, which had been illuminated by a cw HeNe laser oscillating on two axial modes (a-d). The lowest figure shows the ring intensity pattern of an excimer-pumped single-mode dye laser measured behind a FPI with 3.3 GHz free spectral range [187]...

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