Optical and Raman spectroscopies of 171Yb3+:Y2SiO5 hyperfine structure for application toward microwave-to-optical transducer
This study analyzed the optical techniques for high resolution, low-noise spectroscopy of a hyperfine structure (HFS) made of ytterbium-isotope 171 ions ($^{171}\mathrm{Yb}^{3+}$:$\mathrm{Y}_2\mathrm{SiO}_5$). Large energy spacings in $^{171}\mathrm{Yb}^{3+}$ are advantageous for spin-state preparations of quantum memory and construction of a transducer, thereby promoting the simultaneous stable control of the optical frequencies of lasers over a wide range of 3 GHz. We also built our own 2.7-K cryogenic system for optical, radio-wave-assisted spectroscopy. We attained to high resolution and sensitivity both in pump-probe saturation spectroscopy (PPS) and Raman heterodyne spectroscopy (RHS). Our frequency-stabilized PPS achieved a high-resolution spectrum of the HFS, whereas our setup of RHS enabled the efficient detection of paramagnetic spin resonance efficiently for a wide range of radio frequencies. As the underlying Raman process is an up-converting transduction, we present the optimization of the sensitivity of Raman heterodyne detections by selecting the best crystal orientation and efficient radio-wave coupling in future applications toward photon transducers.