Intra-Cavity Frequency-Doubled VECSEL System for Narrow Linewidth Rydberg EIT Spectroscopy

Stable, frequency-tunable lasers are crucial tools throughout various quantum science disciplines including computing, sensing, and timekeeping. Many of these applications require hundreds of milliwatts of output power at visible frequencies approaching the UV that are challenging to achieve directly. Such requirements are often met by using tapered amplifiers, frequency doubling and/or injection locking of additional lasers. Vertical external-cavity surface-emitting lasers (VECSELs) augmented by nonlinear optical frequency conversion offer an alternative method of producing such light with a reduced number of components and excellent output mode quality. Here, we demonstrate the use of such a laser with 690mW of output power at 480nm for Rydberg-state spectroscopy via electromagnetically induced transparency (EIT) in a room temperature vapor of ⁸⁵Rb atoms, observing narrow linewidth EIT with full-width half-maximum of 1.75MHz. We also characterize the laser's frequency stability via the delayed self-heterodyne technique and direct comparison to a commercial external-cavity diode laser (ECDL). To our knowledge, this is the first spectroscopic demonstration of atomic features with widths on the order of 1MHz using an intra-cavity frequency-doubled VECSEL.