A dense system of independent oscillators, connected only by their interaction with the same cavity excitation mode, will radiate coherently, which effect is termed superradiance. In several cases, especially if the density of oscillators is high, the superradiant decay of the oscillators’ excited state may dominate the intrinsic relaxation processes. At low frequencies, this limit can be achieved with cyclotron resonance in two-dimensional electron gases. In those experiments, the cyclotron resonance is coupled to the electric field of light, while the oscillator density can be easily controlled by varying the gate voltage. However, in the case of magnetic oscillators, to achieve the dominance of superradiance is more tricky, as material parameters limit the oscillator density, and the magnetic coupling to the light wave is rather weak. Here we present quasi-optical magnetic resonance experiments on thin films of yttrium iron garnet. Due to the simplicity of experimental geometry, the intrinsic damping and the contribution of superradiance can be easily separated in the transmission spectra. We show that with increasing film thickness, the losses due to coherent radiation prevail the system’s internal broadening.

一个由独立振荡器组成的密集系统，仅通过它们与相同的腔激发模式的相互作用而连接，将相干辐射，这种效应称为超辐射。在某些情况下，尤其是在振荡器的密度很高的情况下，振荡器激发态的超辐射衰减可能会主导固有的弛豫过程。在低频下，可以通过二维电子气中的回旋共振来实现此限制。在那些实验中，回旋加速器谐振耦合到光的电场，而振荡器密度可以通过改变栅极电压来轻松控制。但是，在电磁振荡器的情况下，要达到超辐射的优势比较困难，因为材料参数限制了振荡器的密度，并且与光波的磁耦合相当弱。在这里，我们提出钇铁石榴石薄膜的准光学磁共振实验。由于实验几何的简单性，本征阻尼和超辐射的贡献可以在透射光谱中轻松分离。我们表明，随着膜厚度的增加，由于相干辐射引起的损耗占了系统内部的范围。