Nanosecond time-resolved characterization of a pentacene-based room-temperature MASER

Abstract

The performance of a room temperature, zero-field MASER operating at 1.45 GHz has been examined. Nanosecond laser pulses, which are essentially instantaneous on the timescale of the spin dynamics, allow the visible-to-microwave conversion efficiency and temporal response of the MASER to be measured as a function of excitation energy. It is observed that the timing and amplitude of the MASER output pulse are correlated with the laser excitation energy: at higher laser energy, the microwave pulses have larger amplitude and appear after shorter delay than those recorded at lower laser energy. Seeding experiments demonstrate that the output variation may be stabilized by an external source and establish the minimum seeding power required. The dynamics of the MASER emission may be modeled by a pair of first order, non-linear differential equations, derived from the Lotka-Volterra model (Predator-Prey), where by the microwave mode of the resonator is the predator and the spin polarization in the triplet state of pentacene is the prey. Simulations allowed the Einstein coefficient of stimulated emission, the spin-lattice relaxation and the number of triplets contributing to the MASER emission to be estimated. These are essential parameters for the rational improvement of a MASER based on a spin-polarized triplet molecule.

Unraveling the Room-Temperature Spin Dynamics of Photoexcited Pentacene in Its Lowest Triplet State at Zero Field

“…However, the value of w xz reported in ref. 26 is anomalously high; we have no explanation other than to point out that the authors' model in this paper was two-level and thus could not have captured the full spin dynamics.…”

Room-temperature cavity quantum electrodynamics with strongly coupled Dicke states

“…This so-called "cavity protection" effect, associated with non-Markovian memory effects, is attributed to inhomogeneous broadening of spin transitions with non-Lorentzian lineshapes. [10][11][12] To conclude, this system, which was recently used to demonstrate a solid-state room-temperature maser, 19,20,23 also shows promise as a platform for exploring cavity quantum electrodynamics, spin memories for quantum information processing 16 and quantum-enhanced technologies for metrology, sensing and communications. 27 …”

“…The cavity is similar to the one reported for a miniaturised room-temperature maser which uses a hollow cylinder of STO, but houses a pentacene-doped p-terphenyl crys tal with a much higher concentration of 0.053% mol/mol than in previous studies. 19,20 The TE 01δ mode has a frequency tuned to the e j i $ g j i spin transition, ω c ≈ ω s ≈ 2π × 1.45 GHz. This mode has a magnetic field dipole directed along the cylindrical axis ( Fig.…”

“…The pentacene:p-terphenyl crystal was grown as per the previously reported method 19,20 but with higher concentration of pentacene (see Supplementary Information for details).…”

Growth, morphology and structure of mixed pentacene films

“…The concentration of pentacene has been reported to influence its applicability in optoelectronic applications. Previous literature has reported the use of an optically excited organic mixed molecular crystal for maser applications consisting of pentacene and pterphenyl, where pentacene is present in very low concentrations [8][9][10][11] . Conversely, pure pentacene has been implemented for devices such as organic field-effect transistors and organic photovoltaic devices.…”