The label printing apparatus has a structure including: a label feed means for successively feeding plural labels, each having an information printing area including a heat-sensitive color developing ink layer, to predetermined printing positions; a laser printing device which is provided with a sensor and a light source, said sensor serving to discriminate between presence and absence of the label in the predetermined printing position and to output a label detection signal, said light source serving to release a laser beam, and which receives the label detection signal directly from the sensor, prints information on the label by means of the laser beam when the presence of the label on the predetermined printing position is confirmed by the label detection signal, and outputs a shot signal; and a controller to discriminate whether the output interval between the shot signals is within a given period of time or not and to output an error signal when the output interval between the shot signals is not within the given period of time. Owing to the above-mentioned structure, the label printing apparatus of the present invention can be easily controlled, is free from any useless motion and is able to reduce occurrence of a defective.

A reflective film is formed over a recording surface of an optical disk on which pits are formed. The reflective film is made of a non-linear optical material which, when light is incident thereon, generates second harmonics of the incident light. In a reproduction optical system for reproducing this optical disk, when a reading beam reflected by the reflective film of the optical disk impinges on a filter for filtering out the basic wave of the reading beam, the filter only transmits the second harmonics which are then incident on a light receiver. Since information signals recorded on an optical disk is reproduced by reading only second harmonics of the reflected beam, the cut-off spatial frequency of the OTF can be made twice higher as compared with a conventional reproducing apparatus. In other words, the recording density of the recording medium can be made higher.

The present invention relates to a recording medium comprising a plane substrate and a recording layer containing a polymer liquid crystal compound, wherein said recording layer containing a polymer liquid crystal compound has a groove.

According to the present invention, there is provided a non-linear optical device comprising a non-linear optical medium comprising an organic compound, which remarkably improves the non-linear optical properties. The non-linear optical device according to the present invention is suited for the second and third harmonic generations, photomixing optical parametric oscillations, optical switches and optical bistable devices.

A crosslinked polymer liquid crystal is stretched to provide a polymer liquid crystal layer with a higher degree of uniform alignment than a non-crosslinked polymer liquid crystal. Such a stretched layer of crosslinked polymer liquid crystal is disposed between a pair of substrates to form a liquid crystal device showing a better contrast as a recording medium or display device. The improvement in alignment obtained by stretching of a crosslinked polymer liquid crystal is also effective in increasing the responsive characteristics in response to an electric field or magnetic field and also the pyro-electric effect of the resultant polymer liquid crystal layer where the polymer liquid crystal is a ferro-electric one.