This option adds an input light source port to the SPS-300 body such that an external broadband THz light source can be used instead of the internal mercury arc lamp source. This options also includes an internal motorized flipping mirror to select between the external light source and internal mercury arc lamp source. The internal mercury arc lamp source is turned off when the external light source is used. Without this option, the only available light source is the built-in internal mercury arc lamp source. This option is required in the Spectrum Analyzer configuration where an external source spectra is measured. It is also required in the Materials Spectrometer configuration if the user wish to use an external light source to illuminate the sample other than the built-in internal mercury arc lamp source.
Required for Spectral Analyzer Configuration
The THz light source to be measured in Spectral Analyzer Configuration enters through this external light source port.
Accepts External Light Sources
Sciencetech has designed several external demountable THz light sources that mates with this external light source port. Users can select between a globar, and a gun oscillator at this time with other types on the way. Users can also introduce their own light sources to mate with the external light source port. Sciencetech provides all flange interface drawings for the design of such light sources. Please note that some light sources should share the same vacuum space as the internal SPS-300 optics chamber while some other light sources are designed for operation in ambient atmospheric pressure. This External Light Source port includes a vacuum rated quartz window cap that can be used to seal the port when not in use. Since it is made of quartz, an external light source that operates in ambient atmospheric pressure can be mounted to the external light source port with the quartz window attached.
Transmission Efficiency of Quartz Window Cap
The external light source port is capped with a 6mm thick quartz window to maintain the vacuum environment inside. Quartz allows THz light through with a 97% internal transmission efficiency. However, additional loss due to reflections at the entrance and exit surface of the window (Fresnel reflections) also need to be considered which will reduce the overall transmission efficiency to approximately 75%. Such Fresnel reflection loss would also apply to Polystryrene windows.
Software Control
An internal motorized flipping mirror allows the user to select between the external light port and the internal arc lamp source. The internal motorized flipping mirror utilizes two stepper motors for precision operation and repeatability. These stepper motors are water cooled (for operation in vacuum) and are controlled by the SPS-300 software via two RS-232 linked Sciencetech MD-100 stepper motor controllers. To be specific, the SPS-300 software has an ActiveX feature (flipmirror.dll) that controls the internal flipping mirror. One stepper motor lifts the cam, and the second does the rotation.
Vacuum Compatibility
The external light source port and internal flipping mirror are rated for operation at 10^-3 Torr.