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Polychromators are spectrometers that make simultaneous measurements of the spectral distribution for various wavelengths with the aid of a suitable detector like the photodiode array. without rotation of the grating. As shown in Fig.5, light from A is separated into spectral components by the concave grating and this spectrum is then projected onto the face of the detector (between B1 and B2). The spectral image plane has been designed to be as flat as possible, and aberration characteristics such as coma and astigmatism have been carefully minimized. Select the concave grating most suitable for the application from those listed in Table 3.

The various parameters are explained below.

Groove density N :

The groove density at the center of the concave grating.

Dispersion D :

The value obtained by dividing the wavelength range (λ₁ to λ2) by the detector length L.

Wavelength range Nmλ₁ to Nmλ2 :

The optimum wavelength range for the Shimadzu design. Outside this range, aberrations become larger and imaging performance deteriorates. λ₁ and λ2 respectively represent the minimum and maximum wavelengths.

Detector length L :

Length of detector required for application in the above wavelength range.

Blaze wavelength λB :

The blaze wavelength λB for the mounting parameter and not the blaze wavelength for the Littrow configuration λB(Litt). Refer to Blaze Wavelength under Overview of Gratings for details.

Mounting Parameters (Refer to Fig.5.)

Dimensions W, H, and T :

"W" is the width perpendicular to the grooves. "H" is the height parallel to the grooves. "T" is the thickness at the center. (Refer to Fig.3.)

Code number :

Specify a code number when ordering.

Table 3 Standard Aberration-corrected Concave Gratings for Flat-field Polychromators

Click to expand.
*1 : Nominal blaze wavelength is the wavelength of the maximum diffraction efficiency (target) with the design mounting.
No one to guarantee the wavelength of the maximum diffraction efficiency.
Blazing is performed with an ion-beam etching technology.
The nominal blazed wavelength showned by () on the list shows non-blaze wavelength (Holographic grating).
*2 : Relative efficiency minimum is at the nominal blaze wavelength.
In the interests of product improvement, the external appearance and specifications are subject to change without notice.

Characteristics of Concave BHGs for Flat-field Polychromators

(measurement values for reference only)