Abstract: A diffraction element and an optical head having a diffraction efficiency not changing depending on wavelength of light, wherein the diffraction efficiency setting in configurable in relation to wavelength, are provided. In a diffraction element 10 diffracting light, an optically anisotropic medium 11 having birefringency and an optically isotropic medium 12 are periodically and alternately arranged, and in the optically anisotropic medium 11, a principal axis direction of refractive index ellipse in a plane perpendicular to the optical axis on which incident light is transmitted or in a plane close to the plane, is spirally rotated around an axis in parallel with the optical axis. In particular, the optically anisotropic medium 11 having birefringency can be constituted by a polymer liquid crystal formed by polymerizing a liquid crystal.

Abstract: An adhesive is coated on at least one surface of a thin film of organic material having birefringent properties and a phase-difference producing function, and a fixing substrate having transmitting or reflecting properties is bonded to the thin film of organic material by the adhesive, wherein materials satisfying relations of E1<E2 and E3<E2 where E1 is the linear expansion coefficient of the thin film of organic material, E2 is the linear expansion coefficient of the adhesive and E3 is the linear expansion coefficient of the fixing substrate, and the glass transition temperature of the thin film of organic material being 150° or more, are selected.

Abstract: An adhesive is coated on at least one surface of a thin film of organic material having birefringent properties and a phase-difference producing function, and a fixing substrate having transmitting or reflecting properties is bonded to the thin film of organic material by the adhesive, wherein materials satisfying relations of E1<E2 and E3<E2 where E1 is the linear expansion coefficient of the thin film of organic material, E2 is the linear expansion coefficient of the adhesive and E3 is the linear expansion coefficient of the fixing substrate, and the glass transition temperature of the thin film of organic material being 150° or more, are selected.

Abstract: An adhesive is coated on at least one surface of a thin film of organic material having birefringent properties and a phase-difference producing function, and a fixing substrate having transmitting or reflecting properties is bonded to the thin film of organic material by the adhesive, wherein materials satisfying relations of E1<E2 and E3<E2 where E1 is the linear expansion coefficient of the thin film of organic material, E2 is the linear expansion coefficient of the adhesive and E3 is the linear expansion coefficient of the fixing substrate, and the glass transition temperature of the thin film of organic material being 150° or more, are selected.

Abstract: An adhesive is coated on at least one surface of a thin film of organic material having birefringent properties and a phase-difference producing function, and a fixing substrate having transmitting or reflecting properties is bonded to the thin film of organic material by the adhesive, wherein materials satisfying relations of E1<E2 and E3<E2 where E1 is the linear expansion coefficient of the thin film of organic material, E2 is the linear expansion coefficient of the adhesive and E3 is the linear expansion coefficient of the fixing substrate, and the glass transition temperature of the thin film of organic material being 150° or more, are selected.

Abstract: An ultrasonic delay line device has an adjusting circuit for adjusting delay time provided between two terminals at the power input side of an ultrasonic delay line, wherein the adjusting circuit includes a serial connection of a fixed capacitor and a variable resistor connected between said two terminals of the power input side and a fixed coil connected in parallel with the serial connection of the fixed capacitor and the variable resistor.

Abstract: An ultrasonic-wave delay line element comprises a pentagonal delay medium body formed by cutting at an angle of about 45.degree. a part of the major surface defined by a rectangular shape having two longer sides and two shorter sides, and has a pair of input and output electric-mechanic transducers provided on a side A formed by cutting the major surface. The input and output electric-mechanic transducers are attached to the cut side A at positions near longer side C contiguous to the cut side A with respect to the center of the cut side A; a reflection point for a sound-wave is provided in the cut side A while no reflection point is provided in a shorter side B contiguous to the out side A; two or more reflection points are provided in the longer side C; two reflection points are formed in the other shorter side D isolated from the cut side A; and four or more reflection points are provided in the other longer side E isolated from the cut side A.