Efficiency of grating

Figure 4. The efficiency of gratings used in the Gemini Multiple Object Spectrograph (CMOS) from measurements by the vendor in Littrow configuration.

TR measurements for correspondingly increased rejection of Rayleigh scattering. The addition of each grating typically introduces a throughput efficiency factor of roughly 30%, however, so that the overall efficiency of a... 

However, the usable spectral region is limited by the wa eieiutlJlidcpendent efficiency of the gratings. 

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). 

Fig. 4 shows the efficiency of the set of reflection gratings delivered with the Gemini Multiobject Spectrograph (GMOS) for Gemini-North (Section 2.3). 

Figure 7. Efficiency of a VPH grating with p = 1200/mm =v). The superblaze envelope is...

From the above definition it is quite evident that the sensitivity takes no cognizance of the noise-level of the base-line, therefore, it is more or less of no use as a definite guide to the least quantity of an element which may be estimated. However, the sensitivity of a 1% absorption-is a pure theoretical number only that would undergo a change solely depending on the efficiency of the lamp (hollow-cathode-lamp), atomizer, flame-system employed, monochromator (prism, grating used), and finally the photomultiplier used. 

T. W. Ang, G. T. Reed, A. Vonsovici, A. G. R. Evans, P. R. Routley, and M. R. Josey, Effects of grating heights on highly efficient Unibond SOI waveguide grating coupler, IEEE Photon. Tech. Lett. 12, 59-61 (2000). 

The relative efficiency of a grating (which is typically 45-80%) is defined as... 

Figure 7. The efficiency of the gratings used on the Beckman 4240 spectrometer...

Now, all steps can be combined to calculate the heterodyne diffraction efficiency from Eqs. 9,16,20,21, and 23. After normalization to the diffraction efficiency of the steady state amplitude of the temperature grating, one arrives at... 

As predicted by the expressions for the critical divergence of the Soret coefficient in (12) and (13), the heterodyne diffraction efficiency of the induced concentration grating dramatically increases on approach of the critical point. Figure 2 shows normalized heterodyne diffraction efficiencies that have been recorded for different distances T — Tc. A few hundred milli-Kelvin away from Tc, the modulation depth, which is proportional to the heterodyne signal, exceeds the values typically found for small molecules and off-critical mixtures by nearly four orders of magnitude. 

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