The THz range of electromagnetic waves at frequencies between  Hz, is the subject of active research and technological development in the past decades. With applications ranging from studies of condensed matter physics, through medical imaging to faster wireless communications, there is great demand for good THz sources and detectors [1,2]. However, in-spite of significant advancements in the field, there is still a lack of THz sources that are compact, easy to use and allow control over the properties of the emitted THz waves.

Recently, generation of THz waves from metasurfaces made of 40 nm thick split ring resonators (SRRs) was demonstrated, yielding THz fields at the same order of magnitude as those emitted by sub-millimeter nonlinear ZnTe crystals [3]. In addition, it was shown that a meticulous design of the SRRs’ spatial arrangement allows obtaining unmatched control over the emitted THz waveform [4,5]. These demonstrations mark PMAs as promising candidates for integration in compact THz systems, allowing functionalities that are inaccessible by other means of THz generation.

Until now, however, only amplified laser systems were used to excite SRR based PMAs. The complexity, cost and size of amplified laser systems strongly limit the applications that can benefit from the nonlinear PMAs. Moreover, the use of intense laser pulses may involve several mechanisms in the THz generation process [6,7], complicating the control over the emitted THz waves.

An important step in making nonlinear PMAs beneficial for a wide range of THz applications is exciting them with compact, inexpensive femtosecond lasers. We show it is possible to use an optical parametric laser oscillator, emitting femtosecond pulses with energies of several nanojoule, to drive such PMAs. We use an SRR based PMA, and in spite of the use of low energy laser pulses, the peak field generated by the PMA is equal to that emitted from a 2500-fold thicker ZnTe crystal. The full usable bandwidth of the generated THz light is over 1.5 THz. The amplitude and bandwidth of the THz field allow us to use the PMA as the source in a spectroscopic measurement of the absorption lines of -lactose powder, thus demonstrating the suitability of PMAs for integration and improvement of standard spectroscopic THz systems.

[1] Y. S. Lee, Springer Science & Business Media. (2009).

[2] D. M. Mittleman, Journal of Applied Physics, 122(23), 230901. (2017).

[3] L. Luo, I. Chatzakis, J. Wang, F. B. Niesler, M. Wegener, T. Koschny and C. M. Soukoulis, Nat. Commun. 5, 3055 (2014).

[4] S. Keren-Zur, M. Tal, S. Fleischer, D. M. Mittleman and T. Ellenbogen, Nat. Commun. 10, 1778 (2019).

[5] E. Minerbi, S. Keren-Zur and T. Ellenbogen, Nano Lett. 19, 6072-6077 (2019).

[6] D. K. Polyushkin, I. Márton, P. Rácz, P. Dombi, E. Hendry and W. L. Barnes, Phys. Rev. B 89, 125426 (2014).

[7] G. K. P. Ramanandan, G. Ramakrishnan, N. Kumar, A. J. L. Adam and P. C. M. Planken, J. Phys. D Appl. Phys. 47, 374003 (2014).