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Low Stray Light CCD Spectrometer for UV Performance: Quest™ U

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Quest™ U—a linear CCD array spectrometer from B&W Tek—has been improved for UV performance through a low stray light optical bench.

The spectrometer features an integrated 16-bit digitizer, a 2048 element detector, an external trigger and a USB 2.0 interface with a readout speed of more than 2.0 MHz. The temperature-compensated Quest™ U considerably decreases the thermal drift to approximately 15 counts/°C. This provides better stability by reducing the baseline drift and maintaining the dynamic range.

The Quest™ U spectrometer comes in two regular spectral configurations: 200–850 nm and 200–400 nm. For OEM applications, customized configurations and the RS232 communication interface are also provided. The Quest™ U spectrometer is a crucial building block for complete solutions. For OEM applications, system development and application support are also provided.

Applications

Reflectance
Absorbance
Wavelength identification
NIR UV and Vis spectroscopy/spectrophotometry/spectroradiometry
OEM optical instrumentation component

Features

UV and UV/NIR standard
Low stray UV Light
Plug-and-play USB 2.0
A 16-bit digitizer
A spectral resolution of more than 0.4 nm
A minimum integration time of 1 ms
Readout speed is more than 2.0 MHz

Accessories

Fiber-optic probes
Fiber patch cords
Inline filter holders
Cuvette holders
Light sources

Software

The BWSpec^® spectral data acquisition software has been developed to carry out complex calculations and measurements at the touch of a button. With the help of this software, users can select between numerous data formats and optimize scanning parameters, including the integration time.

Apart from robust data processing and data acquisition, other features of the BWSpec^® include spectrum smoothing, automatic dark removal and manual/automatic baseline correction.

Software

Image Credit: B&W Tek

Specifications

Table 1. Source: B&W Tek

.	.
Power Input	USB @ < 0.35 Amps
Detector Type	Response-Enhanced Linear CCD Array
Detector Pixel Format	2048 x 1 Elements @ 14 µm x 200 µm Per Element
Spectrograph f/#	3.6
Spectrograph Optical Layout	Czerny-Turner
Dynamic Range	1300:1 Single Acquisition
Digitizer Resolution	16-bit or 65,535:1
Readout Speed	>2.0 MHz
Data Transfer Speed	Up to 480 Spectra Per Second Via USB 2.0
Integration Time	1 - 65,535 ms
Thermal Drift	~15 Counts/^oC (~29 Counts/^oC Max)
Aux Port	External Trigger, Digital IOs
Operating Temperature	5 °C - 35 °C
Operational Relative Humidity	85% Noncondensing
Weight	~ 0.8 lbs (0.37 kg)
Dimensions	4.9 in x 3.6 in x 1.4 in (124 mm x 91 mm x 35 mm)
Computer Interface	USB 2.0 / 1.1 and Enhanced RS232
Operating Systems	Windows: XP, 7, 8, 10 (32-bit & 64-bit)

Technical Details of Quest™ U

Image Credit: B&W Tek

1. Fiber Coupler

Secures Fiber to Ensure Repeatable Results

When a fiber optic is coupled to the SMA 905 adaptor, light is directed to the slit and optically matched, guaranteeing reproducibility. A lens or diffuser assembly can be directly linked to the SMA 905 adaptor for free-space sampling.

2. Entrance Slit

Determines Photon Flux and Spectral Resolution

Light penetrating the optical bench of a spectrometer is vignetted by an aligned, pre-mounted slit. This eventually establishes the throughput and spectral resolution of the spectrometer after the selection of gratings. B&W Tek provides an array of slit widths to match the specific application requirements of users. Custom slits are also available.

Table 2. Source: B&W Tek

Slit Option	Dimensions	Approx. Resolution 200-400 nm	Approx. Resolution 200-850 nm
10 µm	10 µm wide x 1 mm high	~0.4 nm	~1.0 nm
25 µm	25 µm wide x 1 mm high	~0.6 nm	~1.5 nm
50 µm	50 µm wide x 1 mm high	~1.0 nm	~2.5 nm
100 µm	100 µm wide x 1 mm high	~1.6 nm	~4 nm
200 µm	200 µm wide x 1 mm high	~3.0 nm	~8 nm
Custom Slit Widths Available

3. Collimating Mirror

Collimates and Redirects Light Towards Grating

Both the collimating mirrors are f/# matched and coated with AlMg₂, which creates a reflectance of about 95% when operating in the UV-Vis spectrum. While aluminum (Al) offers reflectance, magnesium (Mg₂) protects the former from oxidation.

4. Diffraction Grating

Diffracts Light, Separating Spectral Components

The groove frequency of the grating governs two major aspects of the performance of the spectrometer—the spectral resolution and the wavelength coverage.

Upon increasing the groove frequency, the instrument will acquire a higher resolution, but at the same time, the wavelength coverage will also reduce. Inversely, when the groove frequency is decreased, the wavelength coverage increases, thereby affecting the spectral resolution.

The blaze wavelength or blaze angle of the grating is a major parameter for improving the performance of the spectrometer. The blaze angle decides the highest efficiency exhibited by the grating in a particular wavelength region.

Table 3. Source: B&W Tek

Best Efficiency	Spectral Coverage (nm)	Grating
UV	200 - 400	1800/250
UV - NIR	200 - 850	600/250
Custom Configurations Available

5. Focusing Mirror

Refocuses Dispersed Light onto Detector

Both are f/# matched focusing mirrors coated with AlMg₂, which generates a reflectance of about 95% when operating in the UV-Vis spectrum. Aluminum (Al) offers reflectance, while magnesium (Mg₂) protects the former from oxidation.

6. Array Detector

Measures Entire Spectrum Simultaneously

The Quest™ U includes a 2048 x 1 linear CCD array detector with a pixel width of 14 µm and more than 2000 active pixels. When the incident light hits the individual pixels over the CCD, every pixel denotes a part of the spectrum that, in turn, is translated and displayed by the electronics with a specified intensity using the BWSpec^® software.

The noise level and quantum efficiency (QE) of the array detector considerably affects the dynamic range, sensitivity and signal-to-noise ratio of the spectrometer. The spectral acquisition rate of the spectrometer is chiefly governed by the detector response across a wavelength region.

Table 4. Source: B&W Tek