How to configure a spectrometer for your application? The optimal configuration of spectrometer.
In the modular AvaSpec design you have a number of choices to be made on the several optical components and options, depending on the application you want to use the spectrometer for.
This section should give you some guidance on how to choose the right grating, slit, detector and other options, installed in the AvaSpec.
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Wavelength Range
In the determination for the optimal configuration of a spectrometer system the wavelength range is first important parameter that defines the grating choice. If you are looking for a wide wavelength range, we recommend to take an A-type (300 lines/mm) or B-type (600 lines/mm) grating (see Grating selection table in the spectrometer product section). The other important component is the detector choice, Avantes offers 9 different detector types with each different sensitivity curves (see figure 5). For UV applications the new 2048x14 pixel back-thinned CCD detector, the 256/1024 pixel CMOS detectors or DUV- enhanced 2048 or 3648 pixel CCD detector may be selected. For the NIR range 3 different InGaAs detectors are available.
If you want to combine a wide range with a high resolution, a multiple channel spectrometer may be the best choice.
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Optical Resolution
If you desire a high optical resolution we recommend to pick a grating that has 1200 or more lines/mm (C,D,E or F types) in combination with a small slit and a detector with 2048 or 3648 pixels, for example 10 µm slit for the best resolution on the AvaSpec-2048 (see Resolution table in the spectrometer product section ")
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Sensitivity
Talking about sensitivity, it is very important to distinguish between photometric sensitivity (How much light do I need for a detectable signal?) and chemometric sensitivity (What absorbance difference level can still be detected?)
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Photometric Sensitivity
In order to achieve the most sensitive spectrometer in for example Fluorescence or Raman applications we recommend the 2048 pixel CCD detector, as in the AvaSpec-2048. Further we recommend the use of a DCL-UV/VIS detector collection lens, a relatively large slit (100µm or higher) or no slit and an A type grating. For an A-type grating (300 lines/mm) the light dispersion is minimal, so it has the most sensitivity of the grating types. Optionally the Thermo-electric cooling of the CCD detector (see product section AvaSpec-2048-TEC, page 30) may be chosen to minimize noise and increase dynamic range at long integration times (60 seconds).
For optimal UV sensitivity we recommend the back-thinned UV sensitive CCD detector, as implemented in the AvaSpec-2048x14.
For the different detector types the photometric sensitivity is given in table 4, the spectral sensitivity for each detector is depicted in figure 5.
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Chemometric Sensitivity
To detect 2 absorbance values, close to each other with maximum sensitivity you need a high Signal to Noise (S/N) performance. The detector with best S/N performance is the 2048x14 pixel back-thinned CCD detector, next to the 256/1024 CMOS detector in the AvaSpec-256/1024. The S/N performance can also be enhanced by averaging over multiple spectra.
4. Timing and Speed
The data capture process is inherently fast with detector arrays and no moving parts. However there is an optimal detector for each application. For fast response applications, we recommend to use the AvaSpec- USB2 platform spectrometers. When data-transfer time is critical we recommend to select a small amount of pixels to be transferred with the UBS2 interface. Data transfer time can be enhanced by selecting the pixel range of interest to be transmitted to the PC; in general the AvaSpec-128 may be considered as the fastest spectrometer with more than 8000 scans per second.
The above parameters are the most important in choosing the right spectrometer configuration, please contact our application engineers to optimize and fine-tune the system to your needs. On the next page you will find a quick reference table 1 for most common applications, for a more elaborate explanation and configurations, please see section applications in the back of this catalog.
In addition we have introduced in this catalog application icons, that will help you to find the right products and accessories for your applications.
Table 1 Quick reference guide for spectrometer configuration
Application
|
AvaSpec-type
|
Grating
|
WL range (nm)
|
Coating
|
Slit
|
FWHM Resolution (nm)
|
DCL
|
OSF
|
OSC
|
Biomedical
|
2048
|
NB
|
500-1000
|
-
|
50
|
1.2
|
-
|
475
|
-
|
Chemometry
|
1024
|
UA
|
200-1100
|
-
|
50
|
2.0
|
-
|
-
|
OSC-UA
|
Color
|
128
|
VA
|
360-780
|
-
|
100
|
6.4
|
X/-
|
-
|
-
|
256
|
VA
|
360-780
|
-
|
50
|
3.2
|
-
|
-
|
-
|
2048
|
BB
|
360-780
|
-
|
200
|
4.1
|
X/-
|
-
|
-
|
Fluorescence
|
2048
|
VA
|
350-1100
|
-
|
200
|
8.0
|
X
|
-
|
OSC
|
Fruit-sugar
|
128
|
IA
|
800-1100
|
-
|
50
|
5.4
|
X
|
600
|
-
|
Gemology
|
2048
|
VA
|
350-1100
|
-
|
25
|
1.4
|
X
|
-
|
OSC
|
High resolution
|
2048
|
VD
|
600-700
|
-
|
10
|
0.07
|
-
|
550
|
-
|
3648
|
VD
|
600-700
|
-
|
10
|
0.05
|
-
|
550
|
-
|
High UV-Sensitivity
|
2048x14
|
UC
|
200-450
|
-
|
200
|
2.0
|
-
|
-
|
-
|
Irradiance
|
2048
|
UA
|
200-1100
|
DUV
|
50
|
2.8
|
X/-
|
-
|
OSC-UA
|
Laserdiode
|
2048
|
NC
|
700-800
|
-
|
10
|
0.1
|
-
|
600
|
-
|
LED
|
2048
|
VA
|
350-1100
|
-
|
25
|
1.4
|
X/-
|
-
|
OSC
|
LIBS
|
2048FT
|
UE
|
200-300
|
DUV
|
10
|
0.09
|
-
|
-
|
-
|
2048USB2
|
UE
|
200-300
|
DUV
|
10
|
0.09
|
-
|
-
|
-
|
|
|
|
|
|
|
|
|
|
Raman
|
2048TEC
|
NC
|
780-930
|
-
|
25
|
0.2
|
X
|
600
|
-
|
Thin Films
|
2048
|
UA
|
200-1100
|
DUV
|
-
|
4.1
|
X
|
-
|
OSC-UA
|
UV/VIS/NIR
|
2048
|
UA
|
200-1100
|
DUV
|
25
|
1.4
|
X/-
|
-
|
OSC-UA
|
2048x14
|
UA
|
200-1100
|
-
|
25
|
1.4
|
-
|
-
|
OSC-UA
|
NIR
|
NIR256-1.7
|
NIRA
|
1000-1750
|
-
|
50
|
5.0
|
-
|
1000
|
-
|
NIR256-2.2
|
NIRZ
|
1200-2200
|
-
|
50
|
10.0
|
-
|
1000
|
-
|
NIR256-2.5
|
NIRY
|
1000-2500
|
-
|
50
|
15.0
|
-
|
1000
|
-
|
|