Abstract: In the case of a gas in which several gases are mixed, a type and concentration of the gas may be incorrectly measured when measured using only an optical band-pass filter. The invention of the present application is directed to providing a technology in which a plurality of broadband band-pass filters having overlapping regions are provided to calculate a magnitude of absorption for each wavelength band for light passing through each broadband band-pass filter, thereby identifying the presence of a gas of interest and the presence of a gas other than the gas of interest.

Abstract: A laser scanning unit includes an emitting portion for emitting laser beams, a deflecting portion having a plurality of mirror surfaces at its side portions to deflect the laser beams upon a predetermined position of a pickup surface by rotation of a predetermined speed, and a pickup portion for scanning the laser beams deflected by the deflecting portion into the pickup surface. A rotative noise reducing portion is formed at a plurality of edges formed by the plurality of adjacent mirror surfaces of a polygon mirror which acts as the deflecting portion. Preferably, the rotative noise reducing portion includes at least one air groove at the portion where the mirror surfaces connect, so as to be formed around the edges of the mirrors. Thus, it is possible to reduce the pressure difference between the mirror surfaces with the air groove, thereby reducing noise during rotation of the polygon mirror.

Abstract: A recording/reproducing method includes helically scanning a first region of a magnetic tape running at a normal speed using several rotary heads, recording a digital data train on several sloped tracks and simultaneously recording single-frame data at N-picture intervals on a second region of the magnetic tape through at least one fixed head, and reproducing the data recorded on the first region during a normal reproduction, while the magnetic tape runs at an N-times speed for variable speed reproduction to reproduce the data recorded on the second region. In a digital VTR, the recording data for the normal recording/reproduction and special recording/reproduction is separately recorded and reproduced on mutually different regions of the magnetic tape. Accordingly, since the processing of the normal recording/reproduction signal is independent from that of the special recording/reproduction signal, the normal-processing design is facilitated due to a greater degree of freedom.