a) Resonator response to a 122 Hz chopped signal. The TOD has been folded and averaged. We use a higher mode resonance ( ~1 GHz) of the LEKID to measure the quasiparticle lifetime. We fit the tail of the falling edge to an exponential model to find the quasiparticlelifetime τ_qp = 111 μs. The fit is thered line. b) Detector NEP as a function of absorbed power. Plotted in the blue dashed line is the expected photon noise for coherent radiation which is shot noise and GR noise in equal parts. The limiting NEP ₀, at the lowestpowers, is approximately . The devices are photon noise dominated above approximately 1 pW of absorbed power.