Laser power measurement

Figure 3. Scanning electron micrographs of palladium features on quartz substrate as a function of laser power (measured on target) and scan speed. Palladium acetate precursor film thickness is 1.5 pm (cw Ar+ laser - 5145A line, spot size —0.8 pm FWHM).

FIG U RE 9.17 Fluorescence intensity as a fnnction of experimental parameters, (a) Dispersed emission as a function of laser power, (b) Integrated fluorescence intensity as a function of laser power measured at three different pressures of helium trapping gas. (c) Effect of the ion charge control (ICC) value, a relative measure of the number of detected ions, and (d) effect of on fluorescence intensity monitored with two different numbers of trapped ions. 

Figure 4.9 The effect of laser power upon the photobleaching of a freely diffusing spFRET labelled protein. Upon increasing the laser power from 40 to 120 /u,W (top to bottom, laser power measured before the objective, see Chapter 3), the raw data (left, donor channel grey, acceptor channel black) and the calculated proximity ratio histograms (right) both show the increase in donor only fluorescence (increase in donor channel in the raw data, increase in the relative magnitude of the zero peak) that is indicative of photobleaching.

Si (PV) O.l-l.l Communication, fire sensing, light and laser power measurement... 

These devices are used to control other devices as the light level varies. These applications are very much like the laser power measurement, but at visible wavelengths. Bolometers as well as PV silicon and GaAs diodes provide adequate sensitivity and are inexpensive and reliable. For more information, see the Vishay website. 

Surface analysis by non-resonant (NR-) laser-SNMS [3.102-3.106] has been used to improve ionization efficiency while retaining the advantages of probing the neutral component. In NR-laser-SNMS, an intense laser beam is used to ionize, non-selec-tively, all atoms and molecules within the volume intersected by the laser beam (Eig. 3.40b). With sufficient laser power density it is possible to saturate the ionization process. Eor NR-laser-SNMS adequate power densities are typically achieved in a small volume only at the focus of the laser beam. This limits sensitivity and leads to problems with quantification, because of the differences between the effective ionization volumes of different elements. The non-resonant post-ionization technique provides rapid, multi-element, and molecular survey measurements with significantly improved ionization efficiency over SIMS, although it still suffers from isoba-ric interferences. 

Which lasers . The above mentioned accuracy of the tilt measurements can be achieve if there are enough return photons. The average laser power required to get them is 2 x 20 W. Up to now, there is no cw laser available that powerful (see Ch. 14). In addition it raised the problem of saturation of the absorption by Na atoms in the D2 transition. These two problems have justified the development of the modeless laser (LSM) at LSP (Pique and Farinotti, 2003). 

Figure 8.9 shows the temperature at the focusing point of the NIR light for several solvents, measured by the present method, as a function of incident laser power. These plots show that the temperature increases linearly with an increase in the NIR... 

Fig. 5.3.10 (A) Polarization obtained contin- lasers (squares). (B) Actual intensities as uous-flow hp-xenon experiment as a function of measured by 129Xe NMR spectroscopy at xenon partial pressure for two different laser 110.69 MHz using 29-W laser power (triangles) powers, i.e., one 30-W diode array laser (tri- and full laser power (squares). Adapted from angles) and two combined 30-W diode array Ref. [16].

Thorn EMI 9235QB) near the phosphor screen to collect all of the ion signal as the probe laser was tuned over the 0(3Pj) Doppler profile at laser wavelengths of 226.23, 226.06 and 225.65 nm for j = 0, 1 and 2, respectively. The output of the photomultiplier was sent to a boxcar averager gated at the appropriate arrival time. The probe laser power was simultaneously measured with a photodiode in order to normalize the 0(3Pj) signal intensity for fluctuations in laser power. 

The branching ratios into the various 0(3Pj) states were surprisingly difficult to measure. The power dependence of the ionizing laser at the center of the Doppler profile was measured before each scan of the Doppler profile to provide proper normalization of the power dependence. It was found that the combination of our laser power and sample concentration put... 

Although a great deal of data analysis is needed to obtain a value of the optical nonlinearity from this measurement, we can estimate the order of magnitude of the value. The estimate comes from a comparison of this data with that taken on a similar experiment using Si as the nonlinear material. (15) The two experiments used approximately the same laser power and beam geometry, and the linear reflectivity curves were similar in shape and size (the minimum value of reflectivity). Neglecting differences... 

Collection of multiple data sets for each time span, with frequent alternation of the polarization, is an essential feature of our protocol. This provides some protection against the effects of drifts in laser power, photomultiplier quantum yield, and absolute calibration of the TAC, photochemical decomposition of the dye, and any other long-term processes that may alter the measured fluorescence response curves. Separate analysis of each data set is necessary to provide an indication of the uncertainty in run-to-run reproducibility and to detect and delete the rare spurious data set. 

The thermal conductivity of suspended graphene has been calculated by measuring the frequency shift of the G-band in the Raman spectrum with varying laser power. These measurements yielded a value for thermal conductivity of 4840 5300 W m 1 K 1 [23], better than that of SWCNTs, with the exception of crystalline ropes of nanotubes, which gave values up to 5800 W m 1 K 1 [24]. Even when deposited on a substrate, the measured thermal conductivity is 600 W m 1 K 1 [25], higher than in commonly used heat dissipation materials such as copper and silver. 

In general, measuring beads requires less laser power than measuring cells because of their higher index of refraction (n 1.5 for polystyrene beads vs. n 1.37 for cells).15 The optical force imparted to a particle scales with the difference in index of refraction between the particle and the fluidic medium.16 For bead measurements, we typically operate at a laser power of 2.5 W, whereas for cell measurements the laser is operated at 10 W to obtain similar displacements. These relative power levels are in line with the comparative refractive index differences between the two different particle types and water. 

The mby fluorescence method allows us to perform pressure measurements in a short time scale (1-10 s), providing a real-time access for pressure control comparing to the time scale of many solid-state chemical processes. As a matter of fact, real-time pressure measurements are necessary when studying kinetic processes [117], but it is also important to minimize the laser power used for measuring the mby fluorescence in order to avoid undesired photochemical effects on the sample, whenever these are possible. In the case of IR absorption studies, which are commonly used for kinetic purposes, the advantage of using the mby fluorescence method, once photochemical effects are prevented, with respect to the employment of vibrational gauges is that no additional absorption bands are introduced in the IR spectmm. 

---