Calibrated photodiodes

A Q-switched, frequency-quadrupled Nd—YAG laser (X, = 266 nm) and its accompanying optical components produce and focus the laser pulse onto the sample surface. The typical laser spot size in this instrument is approximately 2 pm. A He-Ne pilot laser, coaxial with the UV laser, enables the desired area to be located. A calibrated photodiode for the measurement of laser energy levels is also present... 

An accurate and convenient configuration for measuring luminous efficiency from OLEDs/PLEDs is shown in Fig. 4.5. Because the luminous efficiency strongly depends on the OLED/PLED emission spectrum (even for constant quantum efficiency), an eye-sensitivity filter is mounted directly onto the surface of the calibrated photodiode (see Fig. 4.4) [15],... 

The Cathode Radiant Sensitivity" is the current of the photocathode divided by the power of the incident light at a given wavelength. Measuring the Cathode Radiant Sensitivity requires a lamp, a monochromator and a reference detector, e.g. a calibrated photodiode. The setup is difficult to calibrate due to the various error sources. 

The spectral response of a photoelectrode can be investigated by measuring so-called photocurrent action spectra, in which the photocurrent is recorded as a function of the wavelength at a constant applied potential. One usually also records the intensity of the incident light as a function of wavelength in a separate measurement using a calibrated photodiode. The following information can be obtained from photocurrent action spectra ... 

In contrast to photocurrent measurements, discontinuities in the ICPE spectrum can be easily avoided by using the same combination of wavelength range and long pass filters while measuring the light intensity with the calibrated photodiode. 

Fig. 7. Electro-optical response of cell used for Fig. 4. Top left trace calibrates photodiode output. Mosaic cells show a sharp transient at turn on.

Molecular weights of the copolymers were determined by gel permeation chromatography (GPC) with four p-styragel (Haters) columns calibrated using polystyrene standards. Chloroform was used as the eluate at a flow rate 1.5 ml/min. An LKB-2140 Ultraviolet Photodiode Array detector was used to detect the polymer with a scan range from 190 to 370 nm. 

Fig. 2.6. Schematic illustration of the experimental setup for pump-probe anisotropic reflectivity measurements with fast scan method. PBS denotes polarizing beam splitter, PD1 and PD2, a pair of matched photodiodes to detect p- and s-polarized components of the reflected probe beam, PD3 another photodiode to detect the interference pattern of He-Ne laser in a Michelson interferometer to calibrate the scanning of the pump path length...

Micellar electrokinetic capillary chromatography with photodiode array detection was used for the determination of polyaromatic hydrocarbons in soil [65]. A detection limit of lOpg and linear calibration over five orders were observed. Compared to a standard gas chromatographic analysis method, the miscellar electrokinetic chromatographic method is faster, has a higher mass sensitivity and requires smaller sample sizes. 

M. Glick, K. R. Brushwyler and G. M. Hieftje, Multivariate calibration of a photodiode array spectrometer for atomic emission spectroscopy, Appl. Spectrosc., 45, 1991, 328-333. 

Figure 6. Instrumental schematic for vacuum UV photofragmentation-laser induced fluorescence measurement of ammonia SHGC, second harmonic generation crystal SFMC, sum frequency mixing crystal BS, beam splitter BD, beam dump TP, turning prism CL, cylindrical lens R, reflector TD, trigger diode OSC, oscillator cell AMP, amplifier cell BE, beam expander G, grating OC, output coupler M, mirror BC, beam combiner L, lens A, aperture PD, photodiode SC, sample cell RC, reference cell FP, filter pack SAM.PMT, sample cell photomultiplier REF.PMT, reference cell photomultiplier PP, additional photomultiplier port EX, exhaust and CGI, calibration gas inlet to flow line. (Reproduced with permission from reference 15. Copyright 1990 Optical Society of America.)...

Rotation velocities were calibrated by two methods (1) a slitted piece of cardboard was mounted on the disk shaft and the time response of a photodiode was recorded on an oscilloscope, and (2) plots of the limiting current as a function of K FefCN) concentration in 2 M KC1 yielded straight lines whose slope is oh (D for Fe(CN) - is 6.3 x 10 6 cm2/sec) (39). Agreement between the two methods was better than 10%, and the motor was found to be extremely stable over long periods of time,... 

The concentrations of the individual silymarin compounds and taxifolin were determined by HPLC using a Waters system (Milford, MA) composed of an Alliance 2690 separations module and a 996 Photodiode Array detector controlled with Millennium32 chromatography software. The HPLC procedure was previously described by Wallace et al. (13). Calibration curves were prepared from standard solutions of taxifolin, silychristin and silymarin. The silybinin standard from Sigma contained two distinct peaks, which are further referred to as silybinin A (the first peak) and silybinin B (the second peak). 

Accuracy is a measure of the closeness of a measurement to the true value. Precision is a measure of how reproducible the measurements are. For many detectors, the accuracy of a measurement is maintained by user calibration. For some detectors, however, such as photodiode array detectors, accuracy relies on internal calibration. The linear dynamic range of the detector is the maximum linear response, divided by the detector noise. The detector response is said to be linear if the difference in response for two concentrations of a given compound is proportional to the difference in concentration between the two samples. Most detectors become nonlinear as the sample concentration increases. 

The impact velocity, Vo, was measured by a low-power laser light which strikes a mirror mounted on the impactor carriage. The mirror, with six black lines spaced 10 mm apart, reflects the laser beam into a photodiode which records the passage of the black lines and hence the translation of the impact carriage. The impact velocity, which is a function of the barrel pressure, P the barrel cross-sectional area, A the impactor carriage travel, d and its mass, m, was thus computed. A calibration curve was then established by a straight-line fit of the plot of Vo versus P. 

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