More than just smoke and mirrors: Gas-phase polaritons for optical control of chemistry.

Gas-phase molecules are a promising platform to elucidate the mechanisms of action and scope of polaritons for optical control of chemistry. Polaritons arise from the strong coupling of a dipole-allowed molecular transition with the photonic mode of an optical cavity. There is mounting evidence of modified reactivity under polaritonic conditions; however, the complex condensed-phase environment of most experimental demonstrations impedes mechanistic understanding of this phenomenon. While the gas phase was the playground of early efforts in atomic cavity quantum electrodynamics, we have only recently demonstrated the formation of molecular polaritons under these conditions. Studying the reactivity of isolated gas-phase molecules under strong coupling would eliminate solvent interactions and enable quantum state resolution of reaction progress. In this Perspective, we contextualize recent gas-phase efforts in the field of polariton chemistry and offer a practical guide for experimental design moving forward.

Rovibrational Polaritons in Gas-Phase Methane.

Polaritonic states arise when a bright optical transition of a molecular ensemble is resonantly matched to an optical cavity mode frequency. Here, we lay the groundwork to study the behavior of polaritons in clean, isolated systems by establishing a new platform for vibrational strong coupling in gas-phase molecules. We access the strong coupling regime in an intracavity cryogenic buffer gas cell optimized for the preparation of simultaneously cold and dense ensembles and report a proof-of-principle demonstration in gas-phase methane. We strongly cavity-couple individual rovibrational transitions and probe a range of coupling strengths and detunings. We reproduce our findings with classical cavity transmission simulations in the presence of strong intracavity absorbers. This infrastructure will provide a new testbed for benchmark studies of cavity-altered chemistry.

A versatile platform for gas-phase molecular polaritonics.

Cavity coupling of gas-phase molecules will enable studies of benchmark chemical processes under strong light-matter interactions with a high level of experimental control and no solvent effects. We recently demonstrated the formation of gas-phase molecular polaritons by strongly coupling bright ν3, J = 3 → 4 rovibrational transitions of methane (CH4) to a Fabry-Pérot optical cavity mode inside a cryogenic buffer gas cell. Here, we further explore the flexible capabilities of this infrastructure. We show that we can greatly increase the collective coupling strength of the molecular ensemble to the cavity by increasing the intracavity CH4 number density. In doing so, we can tune from the single-mode coupling regime to a multimode coupling regime in which many nested polaritonic states arise as the Rabi splitting approaches the cavity mode spacing. We explore polariton formation for cavity geometries of varying length, finesse, and mirror radius of curvature. We also report a proof-of-principle demonstration of rovibrational gas-phase polariton formation at room temperature. This experimental flexibility affords a great degree of control over the properties of molecular polaritons and opens up a wider range of simple molecular processes to future interrogation under strong cavity-coupling. We anticipate that ongoing work in gas-phase polaritonics will facilitate convergence between experimental results and theoretical models of cavity-altered chemistry and physics.

The surgeon's role in breast brachytherapy.

Although two-thirds of invasive breast cancers and half of non-invasive breast cancers are amenable to lumpectomy, only about 70% of such patients choose breast conservation. Of that group, up to one-third do not follow-up with radiation therapy despite it being clinically indicated. The reasons include the patient's and surgeon's attitude toward breast conservation as well as the inconvenience and distance of a suitable radiation facility. The advent of shorter courses of radiation therapy may encourage more patients to seek adjuvant therapy. An increasingly popular and more convenient alternative to traditional whole-breast radiation therapy in patients with early-stage breast cancer is accelerated partial breast irradiation (APBI), for which the American Society of Breast Surgeons and the American Brachytherapy Society have promulgated guidelines for candidate selection. Although several methods are emerging, the most widely used brachytherapy technique utilizes the MammoSite single-catheter balloon brachytherapy device. In a best practices symposium convened in 2006, breast surgeons from academic and community practices with extensive experience in balloon brachytherapy developed general guidelines for integrating APBI into a breast surgical practice. Important considerations include patient age, histology, tumor location and size, and breast size. Thoughtful lumpectomy planning is essential to optimize balloon placement. Real-time sonographic guidance is essential as the surgeon should attend closely to volume excised and cavity shape. A cavity evaluation device can act as a place holder while patient suitability for APBI is considered. Many breast surgeons expert in this procedure insert the balloon catheter in the office either through a de novo skin entrance site removed from the lumpectomy incision or through the original incision. Optimally, insertion occurs within 2-3 weeks after lumpectomy. Close and continual communication with the radiation oncologist is essential to assure optimal outcomes. In this review, several key aspects of a successful APBI program from a surgeon's perspective as well as a consensus panel from a best practices symposium on the topic herein are highlighted.