Filters neutral-density

It is also necessary to reduce the intensity of the radiation admitted into the pyrometer, because pyrometer lamp filaments should not be subjected to temperatures exceeding 1250°C. The reduction is accomplished by a screen or screens in manually operated secondary pyrometers they are usually neutral-density filters. 

Fig. 25-2. Double-beam, double-pass transmissometer for measuring smoke density in stacks. A[, chopper wheel A, beam gating wheel A3, aperture D, detector Fj, spectral filter F2, solenoid-activated neutral density filter L, lamp M, half-mirror/beam splitter Rj, solenoid-activated zero calibration reflector R2, retroreflector (alignment bullseye not shown). Design patented. Source Drawing courtesy of Lear Siegler, Inc.

To evaluate the quantity of interest, i.e., the relative change in reflectance, AR/R, a normalization procedure must be used to eliminate the uninteresting common feature /q(X). In Figure 2 the normalization is performed by the variable neutral density filter (VNDF) connected to a servo mechanism. The dc signal from the detector, which is proportional to /o(A.)./2(A.), is introduced into the servo, which moves the VNDF in such a manner as to keep /Q(k)R(k) constant, i.e., /q(X)R(X) = C. Under these conditions the ac signal Iq(X)ARQC) = CARQC)/RQC. ... 

This procedure should be used cautiously as image intensifies can be damaged by too much hght. When the standard microscope filters are replaced by the beam splitter, a neutral density filter should be inserted to protect the intensifier. 

Introduction of metalized neutral density filters in FLIM systems should be done cautiously as artifacts have been observed due to single or multiple reflections between pairs of ND filters. 

To determine optical damage in bulk benzil crystals a Q-switched Nd YAG laser with 1KW peak power, pulse width of 0.1 ps and pulse repetition rate of 500Hz was used. The laser power was attenuated using a set of neutral density filters and focussed onto a bulk benzil crystal using a x10 microscope objective. No optical damage was observed with optical intensities of upto 100MW/cm - Also, no optical damage was observed in benzil cored fibres with similar optical intensities. 

The initiation system consists of a nitrogen laser and the necessary optics to lead the beam to the sample cell. The laser emits pulses at 337.1 nm with 800 ps duration, with a typical repetition rate of less than 5 Hz. The optical components, aligned between the laser and the calorimetric cell, consist of an iris (I), a support for neutral density filters (F), and a collimating lens (L). The iris is used to cut out most of the laser output and allow only a thin cylinder of light to pass through its aperture, set to 2 mm. The laser energy that reaches the cell is further... 

The laser energy can be changed by the interposition of different neutral density filters and measured using the pyroelectric probe, despite being positioned after the cell, because the solution is the same throughout the experiment (T is constant). To keep the experimental conditions identical between calibration and experiment, the measurements have to be normalized by the transmittance factor, according to equation 13.18. 

A substance or device (synonymous with neutral density filter) that reduces the radiant power of incident radiation by a constant factor over all wavelengths within the instrument s operating range. See also Filter... 

Fig. 5 Fluorescence micrograph of siuface photo-graft-copolymerized with (W-dimethyl-amino) propyl acrylamide methiodide (DMAPAAmMel) by UV irradiation through the stripe-patterned projection mask and the neutral-density filter and subsequently stained with rose bengal, and the three-dimensional image, b of the distribution of the florescence intensity in the area shown in a...

Figure 6.12 Experimental two-color setup featuring an IR beamline, to generate intense shaped IR pump pulses, and a VIS probe beamline, to provide time-delayed probe pulses of a different color. Both beams are focused collinearly into a supersonic beam to interact with isolated K atoms and molecules. Photoelectrons released during the interaction are measured by an energy-calibrated TOE spectrometer. The following abbreviations are used SLM, spatial light modulator DL, delay line ND, continuous neutral density filter L, lens S, stretcher T, telescope DM, dichroic mirror MCP, multichannel plate detector.

Tests. Either the neutral-density filters or potassium dichromate solutions are used. 

Neutral-Density Filters. The empty reference filter holder (air reference) and then filters of various transmittance values at 440, 465, 546.1, 590, and 635 nm are scanned (these wavelengths are selected to minimize interaction between the absorbance and wavelength scales of the spectrophotometer being tested [12]). Compare the results with the values in the certificates. The certified values for the National Institute of Standards and Technology (NIST) SRM 930-e series glass... 

Standard reference material (SRM) for wavelength accuracy, stray light, resolution check, and photometric accuracy can be purchased from NIST. Certified reference materials (CRMs) which are traceable to NIST and recertification services can be purchased from instrument manufacturers and commercial vendors [12]. The cost of neutral-density filters and prefabricated standard solutions in sealed cuvettes can be substantial. When purchasing performance verification standards from a secondary supplier other than a national standard organizations such as NIST in the United States and National Physical Laboratory (NPL) in the United Kingdom, make sure that the traceability of the standards are available in the certificates. The traceability establishes the relationship of individual results to the national standard through an unbroken chain of comparisons. 

The femtosecond fluorescence up-conversion setup has been described elsewhere [13,14]. Briefly, a second harmonic (SH) of a home-made chromium-forsterite femtosecond laser tunable from 610 to 660 nm was used to excite the sample (Fig.2) [14]. The pulse duration of the SH pulses was about 50 fs at the full width at half maximum (FWHM). We were successful in the cavity-dumping operation of this laser [14] and kept the repetition rate as low as 4 MHz. Reduction of the repetition rate was necessary to avoid multiple hits of the same location of the sample as small as possible. The excitation intensity, controlled by a neutral density filter before the sample cell, was (0.5-l)xl012 photons/cm2/pulse. Special care was taken to work at the lowest excitation light intensity so that the effect of the exciton-exciton annihilation process was negligible. 

Pt acts like a neutral density filter through a wide wavelength range and can be used in the UV when the film is on quartz. Au has an optical window with maximum transmission at 540 nm. On quartz, Au can also be used in the UV when the conductivity is comparable to Pt. For the visible region, Au films with good transmission and with resistance as low as a few ohms per square can be prepared. Typical optical properties are shown in Figure 11.3 [55]. The electrochemical properties are similar to bulk Pt and Au, as seen in Figure 11.5 [74],... 

Figure 28.5 Current-potential curves for p-GaP under low- to moderate-intensity illumination a 1 M NaCl (pH = 1) electrolyte is employed. Illumination is from a 200-W high-pressure mercury lamp filtered with neutral density filter. Intensity is relative to the full lamp output. The H2/H+ redox potential is -0.3 V vs. SCE in this cell. Thus, this cell yields approximately 400 mV of open-circuit photovoltage. Note that increased illumination increases both the saturation photocurrent and the onset potential. Although the photocurrent is increased at higher light intensities, a calculation of the quantum yield for electron flow indicates that this parameter decreases with increased light intensity.

The densitometer uses a two beam comparator technique of measurement. A single lamp illuminates, through a variable neutral density filter, the emitter of an eleven stage photomultiplier tube. Because the frequency of measurement is five times the AC line frequency and the amplifiers are extremely high gain, the lamp must be operated from a regulated DC source, otherwise, 120 Hz brightness ripple of the lamp is recorded in the data. 

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