A Guide to Configuring a Spectrometer to Improve Performance

The AvaSpec range of line of instruments offers several configuration options to improve the spectroscopic and optical performance of the instrument for specific applications.

This article provides guidance on how to select the right configuration options, such as slit, grating, detector, etc. for the AvaSpec spectrometer system.

Wavelength Range

When determining the optimal configuration of a spectrometer system, the main parameter that defines the appropriate grating choice is the wavelength range. To acquire a wide (broadband) wavelength range, a 300 lines/mm grating called "A" type grating in the Avantes product line is recommended.

For less range but higher resolution, a 600 lines/mm or “B”-type grating can be used. Higher lines/mm gratings offer higher resolution. Although broadband gratings offer excellent flexibility, they may not provide optimum performance for particular applications.

Detector

The wavelength range coupled with the demands of measurement accuracy and speed usually requires a suitable detector for a particular application. Avantes supplies 15 types of detectors with each having different sensitivity curves. Based on general requirements, the AvaSpec range is divided into three groups.

The AvaSpec-Starline contains general purpose UV/VIS instruments with cost-effective PDA and CCD detectors, the AvaSpecNIRLine includes systems with InGaAs arrays for longer wavelength measurements from 900 to 2500nm, and the AvaSpecSensline includes thermo-electrically cooled CCDs and back-thinned CCDs UV/VIS instruments.

The 2048 pixel CCD detectors in the AvaSpec-ULS2048L and AvaSpec-ULS2048 from the StarLine series are suitable for high-speed applications. The 128 pixel PDA detector in the AvaSpec-128-USB2 may be suitable for VIS-only applications where speed and signal to noise are important, and high resolution is not required.

The SensLine instruments can be perfect for low-light level applications such as Raman and fluorescence. The AvaSpecNIRLine comprises 7 different InGaAs detectors for a range of applications.

The AvaSpec line is modular and has excellent inter-compatibility, and thus makes it possible to integrate two or more detectors in a single instrument to provide optimal performance over a wide wavelength range.

Slit Size and Optical Resolution

For high optical resolution, a grating with higher lines/mm (1200- C type, 1800 – D type, 2400 – E type, 3600 – F type) is recommended. This helps in limiting the instrument’s range to a more narrow range. In addition, a detector with 2048 or 3648 pixels and a 10 or 25µm slit is recommended. To achieve the best resolution, the AvaSpec-ULS3648 with a 10µm slit is recommended.

Slit size is another important parameter in ascertaining both throughput and resolution into the optical bench. If resolution is optimized without taking into account the need for throughput, one may not have sufficient light to achieve a stable measurement. For applications where there is no excess amount of light and high resolution is not required, a large slit is recommended to improve throughput into the optical bench. The AvaSpec-RS contains replaceable slit, making the spectrometer a versatile instrument for both high-sensitivity and high-resolution measurements.

Photometric and Chemometric Sensitivity

It is very important to differentiate between chemometric sensitivity and photometric sensitivity. In order to achieve optimum photometric sensitivity, a high quantum-efficiency detector and a high-throughput optical bench may be appropriate.

The instruments in the AvaSpecSensLine are particularly designed for photometric sensitivity. In fluorescence applications, high photometric sensitivity is required and in Raman applications both sensitivity and resolution are required. For these applications, Avantes AvaSpec-HS1024x122- TEC-USB2 and the AvaSpec-ULS2048L-USB2 spectrometer can be used, respectively. To further improve photometric sensitivity, a detector collection lens (DCL-UV/VIS or DCL-UV/VIS-200) is recommended.

In order to detect different absorbance values with maximum sensitivity, a high Signal to Noise (S/N) performance is needed. The AvaSpecSensLine series spectrometers contain detectors that provide optimum S/N performance.

Speed and Timing

For high-speed applications such as measurements involving light sources and pulsed lasers, the AvaSpec-FAST, AvaSpec-128-USB2, AvaSpec- ULS2048L-USB2, or AvaSpec-ULS2048-USB2 spectrometers are recommended.

These instruments support high-speed data acquisition and are capable of starting an acquisition within seconds of receiving an external trigger. Since data transfer time is important for these applications, Avantes’ Store-to-RAM mode allows on board storage of up to 5000 spectra to the instrument RAM buffer.

Conclusion

The above parameters such as wavelength range, detector, optical resolution, slit size, sensitivity, timing and speed are important in choosing the right spectrometer configuration for specific applications.

This information has been sourced, reviewed and adapted from materials provided by Avantes BV.

For more information on this source, please visit Avantes BV.

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