| 摘要 |
PURPOSE:To obtain an electric signal having high fidelity and a small amount of noise by detecting the change of the refractive index of air due to sound transmission with the diffraction intensity of laser light passing through said air and converting the change of said refractive index into an electric signal. CONSTITUTION:An air layer 2 vibrates in response to a sound wave 3 which propagates into the layer 2 from a sound source toward an arrow mark. The laser light of an angular frequency omega sent from a laser source 4 passing through a region of the layer 2 where the refractive index varies with an angular frequency OMEGA receives a phase modulation during the change of the refractive index of the layer 2. Thus a side band wave is produced in a range of omega+ or -nOMEGA (n: integers of 1, 2, 3...) on the basis of omega. In this case, the diffraction intensity of the laser light changes approximately in proportion to the change of the refractive index. Therefore the change of the output of the laser light 5 is detected by a photoelectric transducer 7 through a slit 6 pierced on the optical axis and delivered in the form of an electric signal. These electric signals are amplified by an amplifier 8 to reproduce a sound. This laser microphone device uses no diaphragm at all, and therefore an electric signal having high fidelity and a small amount of noise is obtained. |
