The construction of an ideal spectral sensor is opposed to the physically related fact that the three diametrical contradictions optical resolution, maximum speed and optimum sensitivity can be combined into a single module only within certain limits.
The "sensor triangle" shows the contradictory requirements – the combination of the best optical resolution, the highest sensitivity and the fastest measurement speed.
© A.S. & Co. GmbH
Spectral sensors of A. S. & Co. can therefore be divided into spectrometer with the best possible resolution and spectrometer with the highest possible sensitivity. All devices have in common that, apart from a standard PC fan, they do not contain any moving elements. Thus, for their operation neither a time-consuming centering nor maintenance is necessary. The robustness makes the systems ideal for 24-hour use in the quality control of a production area.
Photodiode arrays, CCD sensors and modules as InGaAs NIR plane grating spectrometer (PGS) of Hamamatsu, Sony and Toshiba form the basis of our spectrometer lines. Their optical properties such as color resolution, sensitivity and radiation parameters are taken into account for the purpose of use in various application areas. In principle the photodiode arrays (PDA) are sensors with the best signal/noise ratio for color measurements. Therefore they can be found in most devices as highresolution standard sensors or as compact modules with enhanced sensitivity by a factor of 20.
Alternatively we provide CCD lines. Their sensitivity can be again significantly increased if they are additionally equipped with a cooling system and the possibility of pixel binning is given.
The sensors are combined with holographic grids into monolithic blocks (Monolithic Miniatur Spectrometer = MMS), and the correlation between grid and sensor can be assigned through module-specific characteristics. Because these characteristics do not vary during the lifetime of the sensor, no subsequent correction is needed.
Monolithic spectrometer modules, example of an MCS Flex Module from Carl Zeiss Optical Sensor Systems
(source photo: Carl Zeiss)
Production quality and the specification of the optimum effectiveness of the wavelength range are further important components on the holographic grating thus determining the resolution of the module as well as the range of the best speed yield. The gratings for the MMS spectrometer family consist of so-called holographic blazed flat field gratings. In addition to the dispersive function, the grating must map the entrance slit on the diode array. Through the spatial variation of the groove density and curved grooves it is achieved that decimal point faults are corrected and the focal curve is flattened (flat field) and thus optimized to the detector's flat structure.
In addition, all spectral sensors contain a highly efficient fiber cross-section converter, with which the diameter of the circular light guide is projected optimally to the rectangular surface of the sensor.
There are modules with spectral ranges between 195 nm and 2200 nm available, which can also be combined with each other. For example, a second module can record the fluctuations in a gas discharge tube, as is normally the case with XBO flashes. This simultaneous online registration enables precisely to take account of the fluctuations in measurements with highest stability requirements.
Example of a spectrometer rack, in which several sensor modules are synchronized
Alternatively, an additional sensor provides for improved detail resolution or the spreading of the measurement range, and last but not least, the entire operating range of the system can be extended by adjusting the sensor characteristics to the requirements of NIR detection.
The optical performance can only be successfully implemented if the primary signal is optimized by high performance electronics. In contrast to simple complete spectrometers, our precision spectrometers are characterized by
- excellent signal/noise ratio,
- impressive wavelength reproducibility,
- minimal drift,
- very good linearity and
- an integrated processor for monitoring and control of all functions.
In addition, the electronic components for solving a specific task are assembled to achieve the best possible signal quality. It is not only a matter of analyzing colors, but we also select the sensors, for example, according to their dynamic range to meet the requirements of the densitometry or for displaying time-critical processes.
Overview of the main spectral sensors for the requirements of microscope spectroscopy
|Spectrometer with High Resolution||Spectrometer for weak Signals|
|No of Diodes||1024||512||512||512||256||256||256|
|Wavelength Range (mm)||195-1000||195-620||360-780||650-1050||190-400||190-720||320-1018|
|Wavelength resolution (nm)||0,8||0,8||0,8||0,8||0,8||2,2||3,2|
|Wavelength Accuracy (nm)||0,5||0,5||0,5||0,5||0,5||0,5||0,5|
|ADC Resolution||16 BIT||16 BIT||16 BIT||16 BIT||16 BIT||16 BIT||16 BIT|
|Shortest Integration Time||12ms||6ms||6ms||6ms||3ms||3ms||3ms|
|Cooled NIR Spectrometer||Cooled CCD Spectrometer|
|Peltier cooled||1 stage||2 stage||2 stage||yes||yes
|No of Diodes||256||256||256||512||1024
|Wavelength Range (mm)||950-1690||1340-2000||950-2150||220-620||220-1000|
|Wavelength resolution (nm)||3,0||3,0||6,0||0,8||0,8|
|Wavelength Accuracy (nm)||1,0||1,0||1,0||0,5||0,5|
|ADC Resolution||16 BIT||16 BIT||16 BIT||14 BIT||14 BIT|
|Shortest Integration Time||3ms||3ms||3ms||6ms||6ms|
Our software SpectraVision Basic
- controls the spectral sensors,
- automatically searches for the optimal dynamic range of your spectrum,
- can generate online spectra with up to 3 ms time resolution
- and includes optimization, storage and export functions
It integrates motorized microscope functions such as
- an automatic dark current correction,
- the attenuation of the illumination without affecting the lamp's stability or
- the integration of motorized stages for XY sample positioning
As interfaces, USB 2.0, RS 232, Ethernet or WLAN are available, depending on the modules used.