Atomic spectroscopy is the observation of electromagnetic radiation absorbed and emitted by atoms. As a tool in fields ranging from astronomy to atomic physics, atomic spectroscopy allows for studying the atomic composition of samples as well as the orbital structure of specific atoms. On-chip atomic spectroscopy devices made through common cleanroom processes would make atomic spectroscopy more readily available.
Here in BYU's IML Cleanroom, we build the ARROW (anti-resonant reflecting optical waveguide) using common cleanroom processes. Rubidium vapor is inserted into the hollow portion of the ARROW for on-chip light-rubidium interaction (Figure 1).
Figure 1 - Model of rubidium loaded ARROW chip. The hollow core connects the rubidium loaded chamber to the unloaded chamber to allow for vapor diffusion through the waveguide. The solid core (dark green) propagates the laser through to the hollow core portion of the waveguide for interaction with the rubidium and out towards the photodetector on the other side. The chambers are vacuumed and the system is heated to increase the vapor pressure of the rubidium.
The rubidium spectrum shows absorption peaks of the two natural isotopes of rubidium (Figure 2). A similar spectrum for the transition from the 5S1/2 to the 5P1/2 state can be obtained using a 794 nm laser. Electromagnetically Induced Transparency (EIT), a mechanism for slow light, can be obtained by using hyperfine structure transitions such as ones shown in Figure 2.
Figure 2 - (a) and (b) Hyperfine splitting for Rb85 and Rb87 is shown respectively. The splitting of the 5S1/2 state causes distinct peaks in the 780 nm rubidium spectrum shown in (c). Doppler and other effects cause smaller hyper-fine splittings, such as in 5P3/2, to be invisible in the spectrum without techniques such as saturated absorption spectroscopy.
In order to facilitate rubidium flow through the waveguide hollow core, we have recently redesigned the ARROW chip to rely more on Knudsen diffusion as opposed to pressure differentials (Figure 3).
On-chip atomic spectroscopy devices would pave the way for the study of on-chip slow light. On-chip slow light devices have potential applications in optical communications, optical switches and interferometry. Being on-chip allows for complex optical systems to be integrated onto the same chip.
This research is done in collaboration with UC Santa Cruz and is supported by the NSF and DARPA.
Figure 3 - The single chamber design allows for more holes in the hollow core, thus increasing rubidium vapor diffusion into the core.
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