“…Presently, IR-FELs are open at many synchrotron-radiation facilities all over the world since the optical emission was first observed at a laboratory level more than 50 years ago [ 31 ]. Various original experimental studies using IR-FELs are reported as follows: ablation of biological tissues [ 32 , 33 , 34 ], alteration of biological functions [ 35 , 36 ], degradation of protein–metal complexes [ 37 , 38 ], optical and spectroscopic imaging [ 39 , 40 , 41 ], structural dynamics of biomolecules [ 42 , 43 ], chemical reactions in the gas phase [ 44 , 45 , 46 ], decomposition of biopolymers [ 47 , 48 , 49 ], nonlinear-optical physics [ 50 ], and observation of terahertz radiation [ 51 ].…”