Microwave spectroscopy system for molecules trapped in low temperature condensed media using opto-thermal detection with superconducting thin-film sensor

Ishiguro, Masazumi; Aratono, Yasuyuki

Simple and widely applicable microwave spectroscopy system for the low temperature condensed media has been developed. We applied the technique of opto-thermal detection with superconducting thin-film sensor (STS) for the detection of very weak absorption signal of molecules trapped in quantum solid and liquid such as solid para-hydrogen (-H) and bulk liquid helium. For the test of the system, the microwave transition of ortho-hydrogen (-H) pair in solid -H was observed. The S/N ratio of the observed spectrum of the G transition at 1.4 K was approximately 8. Ultra high sensitivity of STS makes it possible not only to obtain sufficient sensitivity but also to make the apparatus very simple especially around the sample cell.