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0.3K or 4K bolometer

The type of the bolometer must be chosen by the required spectral range. A Hg lamp was used as a light source on both the Sciencetech SPS 200 and Bruker Vertex 80v spectrometers.

[0.3K and 4K bolometer response]

Curves in the figure:

  • black – spectrum that we get with our SPS 200 and 0.3K bolometers, mounted in the cryostat below the 12T magnet
  • red  – signal from the 4K bolometer directly in front of SPS 200 with the high cutoff filter (FH) similar to the one used with 0.3K bolometer
  • blue and green – spectra obtained with Vertex80v and 4K bolometer, high cutoff filter FH in the sample compartment using the Mylar50 and Mylar6 beamsplitters, respectively.

We see

  1. 4K bolometer gives about 10 times less signal at 4 cm-1 when compared to 0.3K bolo
  2. 0.3K bolometer is about 100 times more sensitive than the 4K bolometer, but the signal at 40 cm-1 is about the same. We lose the signal mainly in our probe for the 12T magnet
    • 2 to 4 times on the polarizer and analyzer in the probe
    • about 10 times is lost in the light pipes
    • we lose additional 50% by applying a higher bias to overcome the 0.3K bolometer loading.

0.3K bolometer has sensitivity 4*10^7 V/W with a 5mm sapphire disk absorber, straight cone exit aperture 5.6mm.
4K bolometer has sensitivity 3*10^5 V/W with a 2.5mm diamond disk absorber, Winston cone exit  aperture 1.6mm. The small cone exit probably contributes to the poor performance of the 4K bolometer at the low end of the spectrum.

The blue and green spectra were measured with Vertex 80v and the 4K bolometer. Here the low frequency cutoff is rather fast, but it is a Michaelson interferometer.

In the following figure we see the noise equivalent power of our 0.3K and 4K bolometers.

[Noise equivalent power of the 0.3K and 4K bolometers]