Researchers have developed a new bolometer – a thermal radiation power detector – with record-breaking characteristics in terms of noise and frequency of reading information. The equivalent noise power was an order of magnitude lower than the previous record, and the response time was almost 100 times better than other low-noise bolometers.
Bolometers measure the thermal power of an incident electromagnetic wave. Initially, such instruments directly determined the change in temperature, but today indirect indicators are usually used.
For example, an electrical resistance can be measured in a superconducting bolometer, which increases sharply even with slight heating near a critical temperature. The range of technological applications of bolometers is very wide and covers chemical sensors, consumer electronics, safety systems, as well as detectors in particle physics and astronomy.
The work of scientists from Finland and the USA, led by Mikko Möttönen from Aalto University, describes the design of a new bolometer based on a double transition between a superconductor and ordinary metal. The created detector has two record parameters at once: it is the quietest and the fastest among the low noise.
The equivalent noise power (ESM) of the new device is 20 zwatt per root of hertz. This characteristic shows how much power the measured signal is required so that the signal-to-noise ratio at the output is equal to one in the frequency band of one hertz or, equivalently, when integrated for half a second. The response time of the instrument, which actually determines the possible frequency of taking readings, was about 30 microseconds.
The bolometer consists of a nano wire of an alloy of gold and platinum with a length of about a micrometer, two hundred nano meters wide and only a couple of tens of nanometers in thickness. This wire is connected to aluminum contacts, which at low operating temperatures of the device are in a superconducting mode. The flow of heat through the device increases the electronic temperature in the wire, which, in turn, increases the inductance of the entire circuit. As a result, the frequency of the oscillating circuit containing the detector changes, which is measured directly.
The scientists note that the achieved parameters are already in demand in a number of applications. In particular, extremely low energies must be recorded when searching for dark species of certain species. For example, in the ADMX (Axion Dark Matter Experiment) experiment, the signal power is expected to be at the level of 10 −22 watts, which, if the previous record holder for low noise with an ESM is used, about 300 zW / Hz −1/2 will require an accumulation time of the order of a thousand hours to achieve the signal ratio to noise per unit.
Scientists also suggest that the development can be useful in the field of quantum computers, both for maintaining the necessary working conditions (usually ultra-low temperatures), and for reading information from qubits. However, in the latter case, the bolometer must be accelerated by about a hundred times. According to researchers, the device can operate in photon counting mode at a speed of up to 100 pieces per second at a frequency of 1.3 terahertz from a heat source with a temperature of 3 kelvin.