JPH0369636B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of controlling the pulse waveform of a Q-switch laser used for dulling a roll using laser light. [Prior Art] Roll dulling methods include shot blasting, electrical discharge machining, and a method of processing the roll surface using a laser. A device for dulling the surface of a roll using a laser was published in 1983.
25557, published by Special Publication No. 60-2156.
The device disclosed in Japanese Patent Publication No. 60-2156 uses a light source such as a YAG laser or a ruby laser to generate a pulsed laser using a Q switch to dull the roll surface. In the dull processing of a roll, it is necessary to perform periodic processing on the roll surface using a pulsed laser having a predetermined frequency, pulse width, peak value, etc. As shown in Figure 2, there are two ways to obtain such a pulsed laser output: one is to pulse continuous wave (CW) laser output using a mechanical optical device (chopper, shutter, etc.), the other is to pulse excitation or Q-switch pulse ( There is a method using a pulsed laser such as the one shown in Fig. 3). Since the Q-switch pulse does not require any mechanical equipment, it has the characteristics that the equipment can be made smaller and simpler than the former, and at the same time, frequency control is easy and the control range is wide. However, as shown in FIGS. 4a and 4b, with the Q switch, when the frequency is changed, the oscillation excitation conditions change, so the pulse waveform, peak output, etc. change simultaneously, making stable dull processing impossible. Also, as shown in Figure 1a, the peak value (P ₁ ) of the first pulse is the same as that of the subsequent pulses (P ₂ ,
P ₃ , P ₄ ...). Furthermore, a normal Q-switch pulse generally has a peak value of 10 ⁵ ~
10 ³ watts (W), half-width (tp) is less than 1 μsec, and the peak value converted to power intensity (W/cm ² ) is shown in Figure 5, which is suitable for dull processing ( It has disadvantages such as not being suitable for drilling (drilling). Furthermore, Japanese Patent Publication No. 60-2156 does not disclose any solutions to the above-mentioned disadvantages. [Problems to be Solved by the Invention] Therefore, the present invention aims to control the non-uniformity of the pulse waveform and the values of the peak value and half-width, which are the disadvantages of the Q-switch pulse laser shown above, to a range suitable for rolled dull processing. This is what I am trying to do. [Means for solving the problem] The mechanism for generating a Q-switch pulse laser will be explained using FIG. 3. That is, a desired excitation energy (light source) is continuously applied to the laser rod 1 located between the reflecting mirrors 3 and 4, and a certain angle is set between the laser rod 1 and the reflecting mirror 4 with respect to the laser oscillation optical axis. fused silica, absorber,
When a high frequency signal source (RF) 5 is applied to the Q switch element 2, which is an electroacoustic element, a diffraction grating is formed inside the fused silica, and diffracted light 6 is generated. As a result, the loss inside the resonator 7 increases,
Energy is stored in the laser rod 1. Next, when the RF applied to the Q-switch element 2 is turned off, the diffraction grating in the fused silica disappears, the diffracted light 6 disappears, and the loss in the resonator 7 decreases. As a result, the energy stored in the laser rod 1 is emitted instantaneously, resulting in a laser pulse having a high peak value. That is, as shown in Fig. 6, Emax is applied to resonator 1.
energy is accumulated, and this is Emin (≒
o w), the laser output is
Form a laser pulse with a high peak value from Pmin to Pmax. Therefore, the inventors thought that by controlling the energy accumulation state (Emax) of the resonator 1, the peak value, half-width, etc. of the subsequent pulse could be controlled, and studied the following specific means. A method of reducing the excitation energy of the light source that excites the resonator 1; this method is the simplest method, but when multiple pulses are generated in groups as shown in Figures 1a and 1b, the excitation energy decreases and the subsequent It was found that pulses P ₂ to _{P 4} disappeared and it was not possible to secure the number of pulses necessary for processing. A method of reducing resonator loss during pulse-off and suppressing excessive accumulation of energy in the laser rod 1; this method is based on Emax−Emin (≒
The method is to reduce the value of ow), that is, to reduce Emax, and the following three methods can be considered. -1: Method of changing the mounting angle and position of Q switch element 2. -2: A method of increasing the excitation energy to the laser rod 1 to a level higher than the transmission blocking upper limit of the Q switch element 2. -3: Method of reducing the RF power applied to the Q switch element 2. As a result of experiments, any of the above three methods generates a steady continuous output P _L ' as shown in Figure 1b, and the ratio of P _L to the total output P _T can be adjusted by these methods. In other words, the peak value of the first pulse P ₁ ′ decreases (P ₁ ′<P ₁ ), and accordingly, it becomes possible to adjust the intra-group pulse peak values P ₁ ′ to Pi′ to the same level. It was found that the pulse half-width tp' becomes wider (tp'>tp). Note that method -1 requires very advanced techniques to adjust the angle and position, method -2 requires a large amount of energy, and method -3 is the simplest and most desirable method. be. An example using method-3 will be described below. [Example] YAG using the present invention and conventional methods
The characteristics of the laser Q switch pulses are shown in a table for comparison. By comparing the table and Figure 5,
It can be seen that the Q-switch pulse waveform can be controlled to a range suitable for dull processing using the method of the present invention. When the roll is dulled using this Q-switch pulse, a crater-shaped hole 11 as shown in FIG. 7 and a heat-affected zone 12 due to leakage output are formed on the roll surface. The convex portion of the crater-shaped hole can impart a predetermined roughness to the rolled steel plate. Furthermore, since the heat affected zone 12 does not have any irregularities, there is no problem in rolling the steel plate. [Effects of the Invention] According to the present invention, it has become possible to control the Q-switch pulse waveform of the continuous excitation solid-state laser to conditions suitable for dull processing. 【table】

[Brief explanation of drawings]

1a and 1b are waveform diagrams showing a comparison of Q-switch pulse waveforms according to the conventional method and the present invention, respectively; FIG. 2 is a perspective view showing a method of pulsing continuous laser light using a mechanical device (chopper);
Figure 3 is a block diagram showing the configuration of a solid-state laser oscillator including a Q-switch element, Figures 4a and 4b
The figures are graphs showing the correlation between the frequency of the Q switch pulse and the pulse waveform, Figure 5 is a graph showing the correlation between laser irradiation conditions and processing phenomena, Figure 6 is a waveform diagram showing the formation mechanism of the Q switch pulse waveform, and Figure 6 is a graph showing the correlation between the Q switch pulse frequency and the pulse waveform. 7
The figures are a sectional view and a plan view showing the state of laser processing of the roll surface by the method of the present invention. 1: Laser rod, 2: Q switch element, 3,
4: Reflector, 5: High frequency signal source, 6: Diffracted light,
7: resonator, 11: hole, 12: heat affected zone.

Claims (1)

[Claims] 1 In a method of continuously outputting pulsed laser from a continuously pumped solid-state laser using a Q switch, the pulsed Waveform non-uniformity, peak value, half width suitable for dull processing, power density P = 5 ×
10 ⁵ ~5×10 ⁶ W/cm ² , half width tp=5×1/10 ⁷ ~1/1
A pulse waveform control method for a Q-switch pulse laser suitable for rolled dull processing, characterized by controlling the pulse waveform to ^0.05 sec.