An infrared thermometer, comprising: a beam splitter configured to split an incident light beam from an energy zone into an infrared light beam and a visible light beam; an infrared detector configured to detect the infrared light beam and to generate a signal indicative of a temperature of the energy zone according to the detected infrared light beam; a sighting device having a sight window, a reticle, a light source configured to emit a reference light beam through the reticle, and an optical module configured to generate a reflected reticle image and to transmit the visible light beam to generate a target image at the sight window, wherein the optical module comprises: a light splitter having a concave reflective surface, wherein the light splitter is configured to transmit the visible light beam to the sight window and to reflect the reference light beam to the sight window to generate the reflected reticle image, and wherein the sighting device is configured to superimpose the reflected reticle image over the target image at the sight window to align the infrared detector with the energy zone; a flat mirror coupled in a light path between the beam splitter and the sighting device, the flat mirror configured to reflect the visible light beam from the beam splitter to the sighting device; a plano lens coupled between the flat mirror and the sighting device, the plano lens configured to reduce a luminous intensity of the visible light beam that is transmitted to the sight window; and an infrared converging lens module disposed between the beam splitter and the infrared detector, the infrared converging lens module configured to converge the infrared light beam to the infrared detector. a beam splitter configured to split an incident light beam from an energy zone into an infrared light beam and a visible light beam; an infrared detector configured to detect the infrared light beam and to generate a signal indicative of a temperature of the energy zone according to the detected infrared light beam; a sighting device having a sight window, a reticle, a light source configured to emit a reference light beam through the reticle, and an optical module configured to generate a reflected reticle image and to transmit the visible light beam to generate a target image at the sight window, a sight window, a reticle, a light source configured to emit a reference light beam through the reticle, and an optical module configured to generate a reflected reticle image and to transmit the visible light beam to generate a target image at the sight window, wherein the optical module comprises: a light splitter having a concave reflective surface, wherein the light splitter is configured to transmit the visible light beam to the sight window and to reflect the reference light beam to the sight window to generate the reflected reticle image, and wherein the sighting device is configured to superimpose the reflected reticle image over the target image at the sight window to align the infrared detector with the energy zone; a flat mirror coupled in a light path between the beam splitter and the sighting device, the flat mirror configured to reflect the visible light beam from the beam splitter to the sighting device; a plano lens coupled between the flat mirror and the sighting device, the plano lens configured to reduce a luminous intensity of the visible light beam that is transmitted to the sight window; and an infrared converging lens module disposed between the beam splitter and the infrared detector, the infrared converging lens module configured to converge the infrared light beam to the infrared detector. a flat mirror coupled in a light path between the beam splitter and the sighting device, the flat mirror configured to reflect the visible light beam from the beam splitter to the sighting device; a plano lens coupled between the flat mirror and the sighting device, the plano lens configured to reduce a luminous intensity of the visible light beam that is transmitted to the sight window; and an infrared converging lens module disposed between the beam splitter and the infrared detector, the infrared converging lens module configured to converge the infrared light beam to the infrared detector.