A phase-conjugate mirror has a length of hollow core photonic crystal multi-spatial mode, polarization-maintaining fiber disposed in a vessel, with a compressible and preferably gaseous medium, such as Xe or CH4, occupying the hollow core of the of hollow core photonic crystal fiber and surrounding the exterior of the hollow core photonic crystal fiber. At least one sealed window is provided in the vessel, the at least one sealed window being optically coupled to at least one end of the length of hollow core photonic crystal fiber.