Measuring cold/cryogenic objects without touching them? A common way to measure temperature on the scale of household objects and cooking is to use an infrared thermometer. The basic idea is to look at the thermal emission of infrared light from an object which is related to the temperature (like blackbody radiation).
I am interested in ways to use non-contact thermometers at low temperatures (below 50 Kelvin). Blackbody radiation quickly becomes very weak in total energy as you cool down, so I don't think that would work. My question is, are there non-contact thermometers that work at cryogenic temperatures (<50 Kelvin)?
For example, I know Raman spectroscopy can be used to measure temperature by looking at frequency shifts and the ratio between energy absorption and loss events (which scales as $e^{E/k_B T}$). I can't find any examples of this technique for low-temperature thermometry though.
As a note, I am not necessarily looking for a cheap or convenient way to do this measurement. I am more interested to know if such devices exist and how they work physically.

 A: I suppose that there are two fundamental limiting factors - the very low emitted blackbody power at low temperatures (resulting in an extremely poor signal-to-noise ratio if an approach similar to the infrared blackbody curve fitting that room-temperature thermometers use were tried) and the troublesome intermediate-temperature regime in which the radiation occurs.
The total scattered power from a blackbody at 50K is of the order of 1 µW/cm^2 in primarily radio wavelengths. The visible and infrared components of this would be extraordinarily small contributions to background intensity, and the approximation is questionable in cold metallic material.
Raman spectroscopy is the answer. One may exploit the asymmetric temperature dependence of Stokes and anti-Stokes phonon scattering intensities to infer temperature:
$$ \frac{I_\text{Stokes}}{I_\text{Anti-Stokes}} \propto \exp \left(\frac{hc\bar{\nu}}{kT}\right) $$
Optical methods for measuring low temperatures have been published in this open access paper.
