Glasses neutral density filters

Neutral-density glass filters NIST SRM 930 series glass filters (440-635 nm, 10%7 20%T, 30%T)... 

The National Institute of Standards and Technology (NIST) provides standard reference materials (SRMs) to verify the wavelength accuracy and accuracy of absorbance (transmittance) readings. SRM 930E for UV- s analysis consists of a set of three neutral density glass filters of standard thickness with nominal... 

The shutter generally carries the holmium oxide filter (used for the calibration of the photodiode array) and the opaque surface used for the measurement of the dark current. Other optional filters can be included in order to afford fast built-in verification procedures for the spectrometer working parameters (e.g., neutral density glass filter for verification and calibration of absorbance scale in the visible domain). 

Linearity checks are performed by using three neutral-density glass filters available from NIST as SRM 930D. These glasses have nominal percentage... 

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... 

Fig. 2. A schematic drawing of the second harmonic imaging experiment and apparatus. KG-1 and 7-54 are coloured glass filters. The 266 nm signal follows the path through the 7-54 filter and the probe beam follows the path through the neutral density filters (ND)...

In contrast to the setup shown in Figure 5, our experiment uses two coaxial laser beams focused onto the sample C by a lens L (Figure 7). The dye laser beam (power 1 to 10 mW) creates the thermal lens in the sample, whereas the helium-neon laser is used only for monitoring development of the thermal lens. To avoid a thermal lens being induced by the helium-neon laser, a neutral density filter F2 reduces the power of its beam to 6 to 7 /xW in the sample. In front of the detector D, an interference filter F, blocks the beam of the dye laser, and a pinhole P is placed such that only light near the optical axis reaches the detector. To monitor the wavelength of excitation Ao, part of the dye laser beam is deflected by a glass plate Gj onto a... 

Figure 7. Thermal lensing experiment. Kr, krypton ion laser Dye, dye laser M, monochromator Gj, G, G3, glass plate A, attenuator S, shutter, L, lens (/ = 200 mm) I, iris diaphragm C, dye cell (path 1 cm) F, interference filter (A = 633 nm) Fj, neutral density filter P, pinhole (diameter d = 1 mm) D Dj, detector HeNe, helium-neon laser.

FIG. 12.5 Setup for Nd YAG and He-Cd laser experiments I, Nd YAG laser 2,4,1064 nm mirrors 3, glass plate S, BBO crystal 6,7, half-wave (X/2) plates 8,9,355 nm mirror pair 10, polarizer 11, color filter 12, 13, lenses 14. thin film sample 15, fast photodiode 16, iris pinhole 17,21, neutral density filters 18, PMT 19, pump damper 20, He-Cd laser and 22, mirror. 

Neutral density filters are used to attenuate the light equally at all wavelengths. They are typically composed of sheets of glass or quartz coated with a metal to obtain the desired optical density. Quartz transmits in the UV and is preferred unless no work will be done using wavelengths below 360 nta Neutral density filters are described by their optical density and can typically be obtained in increments... 

Neutral density filters are either reflecting or absorbing light attenuators, often simply smoked or semi-silvered glass. 

Fig. 14.5 A variety of typical filters, a An interference bandpass filter showing the typical mirrored surface of these types of filter b two square silvered glass neutral density filters and a round neutral density filter of a colloidal dispersion in glass c a series of round, coloured absorption cut-off filters, and d a pale blue glass heat filter e a Wratten filter of dyed gelatin, which is flexible and easily cut to shape f a polariser g a didymium absorption wavelength standard. The 5p UK coin, included top left to give some idea of scale, has a diameter of 18 mm...

Thus, a filter of optical density D = 1.0 has a transmittance T of 0.1 (10%). When two neutral density filters are combined the transmittances are multiplied while the optical densities are added. In Table 6.2 some pairs of D and T values are given. For high-power laser beams, bulk absorbing glasses or combinations of inclined quartz plates (Fresnel reflection) must be used [6.90]. 

---