The optical head of an installation for observation and treatment by a laser beam of an eye comprises a mirror disposed between an observing microscope and a focusing lens for reflecting towards the latter a treatment and a marking laser radiation beam forming a visible envelope of the treatment beam. That mirror has an outer portion intersecting the marking beam only and an inner portion intersecting the treatment beam only. That inner portion has a reflection coefficient which is maximum for the wavelength of the treatment beam and minimum for the wavelength of the marking beam, so that the latter only is allowed to reach the observing microscope after reflection on the zone of the eye to be treated.

A laser device having an infrared laser medium and an aperture member disposed within a resonator in which the mode symmetry is improved. An optical resonator including a total reflecting mirror and a partial reflecting mirror disposed at opposite ends of a gap between electrodes is arranged parallel to an optical axis and orthogonal to a gas flow direction. An aperture member disposed along the optical axis between the mirrors on the side of the partial reflecting mirror has the form of a ring having an axis coinciding with the optical axis. Plural laser beam detecting elements are disposed on the inner peripheral area of the ring. The angular positions of the mirrors are controlled such that a difference in outputs of the detecting elements is minimized.

A lead frame fabricating method and a lead frame fabricating apparatus are provided which can easily fabricate lead frames of fine pattern at a high speed, can improve dimensional accuracy and quality of the lead frames after the fabrication, and can realize mass-production at a lower cost. To this end, when cutting a metal plate 1101 by irradiation of a laser beam, a laser beam 1011 emitted in the form of pulses and having a circular section is converted by a beam section transformer 1020 into a laser beam 1012 having an elongate elliptic section. The section of the laser beam 1012 is rotated on its optical axis by a beam rotating device 1030 so that the lengthwise direction of the section of the laser beam 1012 is coincident with the lengthwise direction of each of inner leads 1013. An optical axis of a laser beam 1015 is revolved along each of concentric paths 161 to 174 around the original optical axis given when the laser beam 1011 is emitted. Alternatively, a laser beam 3011 emitted in the form of pulses and having a circular section is converted by a beam section transformer 3020 into a laser beam 3012 having an elongate elliptic section. The section of the laser beam 3012 is rotated on its optical axis by a beam rotating device 3030 so that the lengthwise direction of the section of the laser beam 3012 is coincident with the lengthwise direction of each of the inner leads 1013.

Acoustic frictional resistance comprises a plate having at least one laser-formed hole therethrough. The plate is formed by positioning a plate preferably one having a thickness smaller than one and one-half milimeters alongside a laser and directing the laser beam so that it cuts a hole through the plate. During the process of producing the resistance, the value of the acoustic friction is measured as a pressure drop of a constant air stream or as an expenditure of electrical energy for an electrically excited electroacoustic transducer. This measurement is then used as a variable or as a standard for controlling the process. Advantageously, a coherent beam is emitted by the laser which is deflected by mirror from a horizontal to a vertical direction and focused by means of a lens to work in a contact-free manner on a workpiece supported on a support member such as a movable table. By moving the table in two coordinate directions, a plurality of bores are formed in a pattern in a workpiece. The workpiece may comprise a plate which may be rectangular, circular, annular, etc.

Illumination angle adjuster (42) for condensing illumination light from a light generator (41) toward a workpiece (25) includes a simple-structured optical member of condenser lens (44). With the simple arrangement, illumination angle of the illumination light to the workpiece (25) can be easily changed by moving the condenser lens (44) along an optical axis of an optical system (37).