GHz resonant excitation of magnons and phonons from tunable optical frequency combs – GigaSpin

Spectroscopic techniques based on laser-matter interactions allow to probe the vibrational and magnetic degrees of freedom in solids by detecting the associated quantized quasi-particles namely phonons and magnons respectively. These methods rely on the inelastic interaction of light with the object of interest spectrally characterized by stock and anti-stock sidebands surrounding the light central wavelength. Current techniques are based on laser illumination with either continuous waves or femtosecond pulses. The most advanced commercially available femtosecond lasers deliver pulses at fixed repetition rates around 100 MHz and up to 1 GHz. On the other hand, the characteristic frequencies of phonons and magnons span from tens of GHz up to the THz level. Frequencies being so far apart, spectroscopy in this context remains limited to time-domain Brillouin scattering also referred to as coherent Brillouin scattering hence in a systematic out-of-resonance regime.
The main goal of the GigaSpin project is to develop an instrument implementing a novel spectroscopy approach that relies on tunable optical resonant excitation where the laser repetition-rate can be continuously varied to match any magnonic or phononic eigen-frequencies of the material under investigation. The setup and the extended capacities of this novel method will be demonstrated by exploring the magnetic and acoustic properties of a chosen set of specific materials.