Liquid Helium Cooled Bolometers are more sensitive than room temperature DTGS or Pyro-Electric detectors in the far-infrared/terahertz spectral region. However, they are more expensive and tedious to operate as liquid helium is required. This detector option includes a customized silicon composite bolometer, pre-amplifier electronics, a helium dewar and interface flange to the SPS-300. The helium dewar cools the detector to 4.2K or 1.7K (depending on version purchased) for high sensitivity. In the 1.7K version, an added helium pump connected to the dewar is required. In rapid scan mode, the bolometer interfaces to the AD board (included in the Rapid Scan Mode Upgrade) and in Step and Integrate mode, it interfaces to the Lock-in amplifier which in turn has a GPIB interface to the computer (this lock-in amplifier is already included as part of the base SPS-300 system). However, if this bolometer is purchased separate of the SPS-300, a lock-in amplifier data acquisition system is required.
 
Please specify the version (1.7K or 4.2K) once you placed the order.
Detailed Description
This helium cooled composite silicon bolometer is designed specifically for terahertz FTIR applications which provides 10² - 10⁴ higher signal to noise than uncooled pyro-electric detectors. The 4.2K version is recommended for wavelengths from 20~100um, although it has sensitivity up to 300um. The 1.7K version is recommended for wavelength regions from 100um to the millimeter range.
At the heart of the detector is a composite silicon bolometer with a diamond absorber mounted within a shaped cavity at the rear of a Winston cone optic. A fixed far-infrared long wave-pass filter is mounted ahead of the cone to define the spectral response. A suitable vacuum window and cooled load resistor completes the system.
Liquid Helium Cooling
The dewar contains a main core and outer shield vessel. Both vessels are filled with Liquid Nitrogen first for precooling. Once cooled, the liquid nitrogen in the main core vessel is removed and replaced with liquid Helium while the outer shield vessel remains filled with liquid nitrogen. Once filled, the dewar remains cool at 4.2K or 1.7K for 20~24 hours.
1.7K Version has addition Helium Infrastructure Requirements
For the 1.7K version, an additional helium pump with a fine needle valve adjustment is required to support the dewar. This allows a constant supply of fresh liquid helium into the dewar. This external pump is not included with this 1.7K price. Please ask a Sciencetech Applications Specialist for assistance. Although the cost of an external helium dewar pump is not expensive, the continuous liquid helium infrastructure to support it can be.
Sensor Head
The sensor head consists of a diamond absorber which measures 2.5mm x 2.5mm. The actual sensor itself is underneath this absorber and measures 1mm x 1mm.
Rapid Scan Mode
In Michelson operation, the detector interfaces with the SPS-300 16-bit AD board via a digital filter and amplifier. The modulation two blade chopper and lock-in amplifier is not required. In Martin-Puplett Polarizing operation, the detector also interfaces with the SPS-300 16-bit AD Board via the digital filter and amplifier. The output beam needs to be "filtered" with either a fixed grid polarizer analyzer or rotating grid polarizer in a fixed analyzer position.
Step and Integrate Mode
In Michelson operation, the detector interfaces with the lock-in amplifier for synchronization with the input two blade chopper which modulates the input light. In Martin-Puplett Polarizing operation, the detector also interfaces with lock-in amplifier for synchronization with the output rotating grid polarizer chopper/analyzer.
Detector Interface

Please note that this detector price does not include the lock-in amplifier and chopper interface for Step and Integrate mode, nor the digital filter with 16-bit AD Board for Rapid Scan mode. These detector interfaces are included with the base SPS-300 system and Rapid Scan Mode upgrade respectively.

Input focal ratio

3.8

Spectral response

600 cm^-1 to 200 cm^-1

NEP.

~ 3.0 x 10^-13 w/Hz^1/2

Spectral response

375 cm^-1 to 4 cm^-1

NEP.

~ 2.5 x 10^-13 w/Hz^1/2

Spectral response

100 cm^-1 to 3 cm^-1

NEP.

~ 1.5 x 10^-13 W/Hz^1/2