Method Measures Loss of Signal in Far-Infrared Instruments

Scientists from SRON and TU Delft have developed a method to measure the signal loss in far-infrared instruments, designing a signal-carrying so-called microstrip for DESHIMA-2, a far-infrared instrument for the Atacama Submillimeter Telescope Experiment (ASTE) in Chile. The microstrip loses only 1 in 4900 photons.

DESHIMA-2 is the successor to DESHIMA, which was invented by researchers from SRON Netherlands Institute for Space Research and TU Delft. It is being developed by researchers from those institutions with collaborators in the Netherlands and Japan. Far-infrared radiation consists of some of the few wavelengths that our atmosphere allows to pass through.

ASTE telescope in Chile, including DESHIMA and in the future, DESHIMA-2. Courtesy of Denys.

Because early galaxies are so far away and planetary systems are so dim, researchers must be careful with the sparse light they collect with telescopes, even those systems with very large dishes. The DESHIMA hardware team, led by Jochem Baselmans (SRON/TU Delft), seeks to reduce the loss of signal. The incoming signal bounces back and forth hundreds of times before having traveled the required distance to the detector, amplifying the loss with each bounce. Reducing the loss at each bounce therefore reduces the total loss dramatically. For DESHIMA-2, the team aims to reach a loss of only 0.02% per bounce.

“To study early galaxies in more detail, we need a spectral resolution of 500,” Baselmans said. “In that case, even if you lose 0.2% per bounce, you have lost half the signal when it reaches the detector. We need to get the loss down to 1 in 5000, so 0.02% to preserve most of the collected radiation from space.”

The team is close to achieving its target loss, with the microstrip that transports the signal at a loss of 1 in 4900. The researchers noted that the most difficult part may not have been reaching that level, but instead precisely measuring that the microstrip is in fact at that level.

To define a microstrip, scientists want to know the so-called internal loss. Subtracting the outgoing signal from the incoming signal yields a combination of the internal loss and the coupling loss, which happens when the signal bounces and necessitates distinguishing between the losses.

“With other methods you need to know how large the incoming signal is,” said Sebastian Hähnle, who led the work. “That requires expensive and complex experiments. My method does not need that.”

Hähnle created a chip with four microstrips of varying lengths. The longer the microstrip, the less the signal needs to bounce to travel the required distance, so the coupling loss decreases as the internal loss remains the same. Comparing the total loss of all four microstrips enables researchers to deduce the internal loss of each of them.

The research was published in Physical Review Applied (www.doi.org/10.1103/PhysRevApplied.16.014019).