Ultralow-threshold Yb^3+:SiO_2 glass laser fabricated by the solgel process

Abstract

A Yb-doped silica microcavity laser on a silicon chip is fabricated from a solgel thin film. The high-Q microtoroid cavity, which has a finesse of 10,000, is evanescently coupled to an optical fiber taper. We report a threshold of 1.8 W absorbed power that is, to the best of our knowledge, the lowest published threshold to date for any Yb-doped laser. . In addition, the rare-earth aggregate emission spectrum spans many key wavelengths from 0.3 to 3 m that are important for imaging, sensing, medical treatment, and communications. While rareearth lasers have been built in large form factors for high-power laser cutting and defense applications, they can also be designed to be small, low power, and ultrasensitive to the environment. The laser resonator finesse, defined as the free spectral range (FSR) divided by the resonance linewidth, quantifies the loss and hence energy storage efficiency of a resonator. For a given cavity, higher finesse results in lower threshold for lasing. Lacovara et al. measured a 71 mW threshold for a Yb 3+

Ultralow-threshold laser and blue shift cooperative luminescence in a Yb3+ doped silica microsphere

“…Ultralow-threshold Yb 3+ : SiO 2 glass microsphere laser has already been reported. 3,4 On the other hand, other attractive phenomena of Yb 3+ are CL and cooperative absorption, which have been investigated in Yb 3+ doped solid states since 1970s. 5,6 In the first case, Yb 3+ ion-pairs are excited by IR (1-μm) radiation simultaneously, and emit a photon with double energy (in the 0.5 μm region), while Yb 3+ ion-pairs are allowed to absorb the visible in the second case.…”

“…Silica microsphere resonators with whispering gallery modes (WGMs) posse the characteristics of ultrahigh quality factor (Q) and small modal volumes, which can drastically reduce the pump power required to generate laser emission and nonlinear effects. 3,18 Moreover, they can induce strong coupling between the atomic systems and cavity electromagnetic modes. 19 The coupling efficiency between pump laser and YDSM directly affects the power density of WGMs.…”

Yb-doped glass microcavity laser operation in water

“…In this Letter, a Yb: SiO 2 microcavity laser that operates in water is demonstrated. The work builds upon a recently reported, ytterbium-doped silica microtoroid laser with record-low threshold operation in air [8]. To the best of our knowledge, laser action of a microcavity has not yet been demonstrated in water and provides an important new feature for active biosensing applications.…”

“…These devices feature exceptionally high passive Q factors, making them well suited for laser applications when properly doped. In previous work, the solgel method has been used to dope the microcavity with erbium or ytterbium [8,10]. Ytterbium is a more suitable rareearth dopant than erbium for laser operation in water because the absorption coefficient of water is 0.16 cm −1 at 1.04 m (Yb 3+ emission) compared to 10 cm −1 at 1.55 m (Er 3+ emission) [11].…”

“…The ytterbium-doped silica gain medium is fabricated on a silicon chip according to the solgel chemical synthesis method previously reported [8]. To briefly summarize, tetraethoxysilane, water, isopropyl alcohol, hydrochloric acid, and ytterbium nitrate are mixed in specific quantities at 70°C for 3 h to produce the solgel.…”