![]() ![]() The emitted radiation escapes from the cavity in the form of outgoing monochromatic waves, usually along preferred spatial directions. It is well known that an amplifying medium embedded in an optical cavity, i.e., a laser oscillator, can emit coherent electromagnetic radiation when the gain coefficient of photons in the medium reaches a threshold value that balances the light leakage out of the cavity. ![]() The peaks in the coherent reflection curves correspond to the odd- and even-symmetric modes sustained by the slab structure. The dashed black line depicts the spectral reflection curve for incoherent input waves. The red and blue lines show the spectral reflection curves for coherent input waves with controlled phase difference Δ θ ( Δ θ = 0, blue curve Δ θ = π, red curve). (c) Typical behavior of total intensity reflection coefficient versus frequency in a simple two-port photonic device, comprising a slab of lossy material (like Si) of thickness a embedded in a fiber or waveguide (inset), excited at the two input sides. (b) Schematic of the time-reversed laser oscillator that realizes a coherent perfect absorber: when the gain medium is replaced by an absorbing medium with complex refractive index n * = n ′ − i n ′ ′, incoming waves with definite phase and spatial pattern are fully absorbed in the medium. The peaks in the coherent reflection curves correspond to the odd- and even-symmetric modes sustained by the slab structure.įigure 1: (a) Schematic of a laser oscillator: a gain medium with complex refractive index n = n ′ + i n ′ ′, embedded in an optical cavity, emits outgoing coherent waves with defined phase and spatial pattern at frequency ω 0 when the amount of amplification n ′ ′ reaches a threshold value. ![]() Figure 1: (a) Schematic of a laser oscillator: a gain medium with complex refractive index n = n ′ + i n ′ ′, embedded in an optical cavity, emits outgoing coherent waves with defined phase and spatial pattern at frequency ω 0 when the amount of amplification n ′ ′ reaches a threshold value. ![]()
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