Gratings, diffraction blaze

Fig. 18. Spectral dispersion at a diffraction grating, a Grating constant, / Blaze angle, t/tp. angle of incident radiation, 2. angle of diffracted radiation with wavelength X.

Diffraction gratings may be made by a holographic process, but blaze characteristics cannot be controlled and their efficiency is low in the infrared. They are mostly used for low-order work in the visible and near-ultraviolet. 

Question. A diffraction grating has a ruled area that is 10.40 cm wide, has 600.0 grooves per millimetre and is blazed at an angle of 45.00°. 

This section refers to classically-ruled plane diffraction gratings where the grooves have a blazed profile as illustrated in Fig. 2a. 

Figure 2. (a) Blaze condition for a reflection grating, (b) diffracted intensity for unblazed... 

The variation of grating efficiency with wavelength shown in Fig. 2c is based on a simple model of diffraction which is valid for a > A. For finer rulings, polarisafion and resonance effects complicate the situation (Palmer 2000). In the simple case, the efficiency drops to 40% of the peak (blaze) value at the following wavelengths (Schroeder 2000). 

Apart from using the grating in zero order so that it works like a mirror, maintaining a (compact) round beam at the camera (A = 1) requires that the spectrograph adopt the Littrow configuration for which Tf = 0 and the incident and diffracted rays are parallel. From equations 6 and 9, the resolving power at blaze in the Littrow configuration is... 

Fluorescence Instrumentation and Measurements. Fluorescence spectra of the FS samples were obtained on a steady state spectrofluorometer of modular construction with a 1000 W xenon arc lamp and tandem quarter meter excitation monochromator and quarter meter analysis monochromator. The diffraction gratings In the excitation monochromators have blaze angles that allow maximum light transmission at a wavelength of 240 nm. Uncorrected spectra were taken under front-face Illumination with exciting light at 260 nm. Monomer fluorescence was measured at 280 nm and exclmer fluorescence was measured at 330 nm, where there Is no overlap of exclmer and monomer bands. 

Figure 3. Emission spectra obtained from an induction coupled plasma with an ultrasonic nebulizer (for sample introduction). Aim spectrometer, JACO model with a diffraction grating blazed at 250 nm, and a slit width of 20 pm, was used. The spectral resolution was 10.3 nm/500 channels = 0.0206 nm/channel. (a) Emission spectrum of a 1 pg/l bertjlium, 1% HNOj solution, (b) Emission spectrum of a 1% HN03 blank solution, (c) Difference spectrum obtained by subtracting spectrum (b) from (a). Spectra were obtained after an on-target integration for 8 sec.

Fig. 5 Diffraction grating. Ng = normal to the grating Nf = normal to the face of the grating A = angle of incidence 0 = angle of diffraction d = grating spacing and B = blaze angle.

The fluorosensing detection assembly contains an 11-cm diameter transmission diffraction grating that is blazed for 480 nm and has 600 grooves/mm. An 11-cm diameter simple lens brings the dispersed radiation to the entrance surface of 40 quartz light guides. These guides are optically coupled to two separate banks of 20 RCA 8644 photomultiplier tubes (PMTs) of which only 32 were used. 

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