| 摘要 |
1373181 Drilling with laser beams TURLABOR AG and PIERRES HOLDING SA 14 March 1972 [29 March 1971] 11815/72 Heading H1C A laser for drilling holes in materials such as watch jewels or metals has a pulsed output, each pulse comprising a series of equi-spaced spikes the first of which has the greatest amplitude while the remainder have amplitudes which are either the or same as one another which diminish along the series. The alternative forms of pulses are shown in Figs. 2 and 3. The production of a first spike 1, of greater amplitude than the remainder is achieved by operating the laser so as to oscillate in a single transverse mode, which may be fundamental or a higher order. The initial spike serves to heat the workpiece to a point where its absorption coefficient is significant (in the case of a transmissive material, e.g. ruby) or to a point where its surface reflectivity is significantly reduced (in the case of a metal). The spacing between spikes allows vaporized material to escape from the hole. To produce the spikes the Q of the resonator of the laser may be partially spoilt by a modulator consisting of a Kerr cell, Pockels cell, acoustic cell or a saturable absorber, Fig. 6 (not shown), the modulation depth determining whether the output is as shown in Fig. 2, or as in Fig. 3; alternatively one of the resonator mirrors may be mounted on a piezoelectric crystal, Fig. 7 (not shown). The modulator is controlled by an alternating current source having a frequency selected in accordance with the desired repetition period of the spikes. The resonator output mirror has a reflectivity of 80-90% which is stated to cause the production of powerful spikes. |
