3D Laser Cavity Simulator

This is the 3D companion to the Laser Simulator: the same laser rate equations — dN/dt = Rp − N/τ − g·N·φ for the population inversion N, and dφ/dt = g·N·φ − φ/τc + spontaneous emission for the intracavity photon number φ — now drive a genuine, freely-orbitable Three.js resonator instead of a flat side-on canvas. The cavity photon lifetime τc is computed from the real formula τc = 2L / (c·(−ln(R1·R2))), so raising the output-mirror reflectivity or lengthening the cavity measurably lowers the pump threshold shown live in the readout, exactly as it does in a physical laser. Push the pump slider past that threshold and watch the population inversion climb, the intracavity photon count spike through a relaxation oscillation, and a real output beam — colored by the wavelength slider via a genuine wavelength-to-RGB mapping — punch through the partially-transparent output coupler onto the target screen.