CN87103899A - A Q-switched laser pulse waveform adjustment method - Google Patents
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Abstract
一种调Q激光脉冲波形调整方法。该方法通过压缩调Q激光脉冲的后沿宽度，可使调Q激光脉冲宽度大大压缩；并能获得峰值功率恒定的，脉冲宽度连续可调的激光Q脉冲；还可以在保证激光横向模式不变的前提下连续调整Q脉冲峰值功率。此方法简单可靠，适用于一功调Q激光器。
A Q-switched laser pulse waveform adjustment method. By compressing the trailing edge width of the Q-switched laser pulse, the method can greatly compress the Q-switched laser pulse width; and can obtain a laser Q pulse with constant peak power and continuously adjustable pulse width; it can also ensure that the laser transverse mode remains unchanged. Under the premise of continuous adjustment of Q pulse peak power. This method is simple and reliable, and is suitable for one-power Q-switched lasers.
Description
The invention belongs to the technical field of laser.
The Q-switched laser has the characteristics of high peak power and narrow pulse width, so that the application field of the Q-switched laser is gradually widened. Meanwhile, the performance requirements for Q-switched lasers are also increasing, for example, the pulse width is required to be narrower, and in many applications, the pulse width is required to be continuously adjustable, and so on.
Theoretical analysis of the Q-switching process shows that the output peak power and the pulse width of the Q-switching laser depend on the on-off speed of a Q switch, the cavity gain and the cavity loss. Therefore, the first method of compressing the pulse width mainly includes increasing the turn-on speed of the Q-switch, and selecting a high-quality laser working material to increase the pumping power and reduce the cavity loss. These methods have the advantage of being able to increase the peak power while compressing the pulse width, and have the disadvantage of being difficult to implement. In fact, there is essentially no potential to compress the pulse width using the above method. Therefore, further pulse width compression requires development and research on the Q-switching mechanism.
At present, the methods for compressing the Q-pulse width used abroad are mainly the method for emptying the cavity described in US-4477905 and US-4174504, and the United states "optical communications": journal (Optics Communications) VoL.40 No. 4, page 298, describes a self-implant process. Both methods are theoretically effective. The self-injection locking technique also allows continuous adjustment of the laser Q-pulse width. However, they have the disadvantage of being too complex and highly susceptible to external disturbances and are not currently practical. Further, JP-61015384 describes a method of adjusting the acousto-optic Q-switched pulse width, but this method can only obtain a pulse wider than the ordinary Q-switched pulse width, i.e., cannot compress the pulse width.
In summary, the present invention is directed to a simple and feasible method for compressing and continuously adjusting the Q pulse width.
The content of the invention comprises:
the principle of a conventional Q-switched laser is to place the cavity in a low Q-state (i.e., turn off the Q-switch) at the start of pumping. The gain in the cavity is made lower than the loss, preventing the formation of optical oscillations, and thus allowing the pump energy to be stored in the active medium. When the stored energy reaches the maximum value, the resonant cavity is suddenly made to be in a high Q value state (namely, a Q switch is turned on). At this time, the gain is much larger than the loss, and the energy stored in the active medium is rapidly output in the form of one giant pulse.
After the Q switch is turned on, the Q switch is turned off again in the Q pulse output process, so that the working state of the laser resonant cavity is changed, and the waveform of the Q pulse is adjusted. The moment when the Q switch is turned off again can be when the Q pulse reaches the peak value, the Q switch is in the maximum possible off state again, and the waveform trailing edge of the Q pulse is attenuated quickly to achieve the purpose of compressing the width of the Q pulse. The invention can adjust the decay speed of the back edge of the Q pulse by adjusting the loss coefficient after the Q switch is turned off again or adjusting the time of the Q switch to be turned off again, so that the width of the Q pulse is continuously adjusted. The invention can also adjust the peak power of the Q pulse, the Q switch is restored to a high loss state before the Q pulse reaches the peak value, the Q pulse can not reach the peak value, the maximum value which can be reached by the Q pulse can be adjusted by adjusting the time for turning off the Q switch again, and at the moment, the peak power can be continuously adjusted under the condition of constant pumping power. The method for adjusting the peak power of the Q pulse is characterized by being convenient for automatic control, and being unnecessary to adjust the pumping power when adjusting the peak power, which is particularly useful for a solid laser because the transverse output mode of the solid laser can be ensured to be unchanged.
By theoretical analysis, we find that the trailing half-width of the Q-switched giant pulse is always much larger than the leading half-width. In fact, the pulse width of the Q-switched giant pulse is mainly composed of the half width of the trailing edge. This is because the loss in the cavity (excluding the output mirror transmission loss) is always made as small as possible in order to ensure that the peak power of the Q-switched giant pulse is as large as possible. This is beneficial to increase the peak power of the pulse and make the leading edge of the Q-switched giant pulse rise as fast as possible, but is also beneficial to the attenuation of the trailing edge of the pulse, so that the trailing edge of the Q-switched giant pulse is dragged to be very long. In fact, this part of the energy of the trailing edge of the pulse is of little use in many situations. Particularly in the case of laser processing and the like, its presence is sometimes disadvantageous. Therefore, it is necessary to attenuate the trailing edge of the Q-switched macropulse. The method for compressing the pulse width can achieve the purpose, can continuously adjust the width of the Q pulse in a larger range, and simultaneously ensures that the peak power of the Q-switched giant pulse is unchanged. In addition, the method of the invention can also continuously adjust the peak power of the Q pulse on the premise of ensuring that the transverse mode of the laser is not changed.
The invention has the advantages that:
the range of the compressed pulse width is large. Because the trailing edge of the Q-switched giant pulse width is the main part forming the pulse width of the Q-switched giant pulse, the method of the invention can quickly attenuate the trailing edge part, thereby compressing the pulse width in a larger range;
the contradiction between the trailing edge and the leading edge (main component of peak power) of the Q-switched giant pulse is solved. Because the leading edge and the peak power of the Q pulse require that the cavity loss is as small as possible, and the trailing edge requires that the cavity loss is as large as possible, the invention not only keeps the leading edge part, but also compresses the trailing edge part, thereby properly solving the contradiction;
the peak power can be kept constant while the pulse width is compressed, since the invention enables the Q switch to be closed again after the pulse reaches the peak value. Therefore, the method has no influence on the leading edge forming process of the Q pulse, so that the peak output power is not influenced;
simple, easy to implement, reliable and strong in adaptability. The invention can be applied to all Q-switching modes, and has better effect particularly in the fields of laser micromachining, laser ranging and the like.
Description of the figures and examples
FIG. 1 is a schematic view of the apparatus of the present invention. The Q-switched laser consists of a laser working substance (1), a total reflection mirror (2), an output mirror (3), a pumping power supply (4), a Q-switched element (5) and a Q-switched control power supply (6). The laser working substance (1) is any laser material capable of regulating Q, and has high enough energy storage characteristic to ensure the completion of Q regulation. For example, solid Nd: YAG crystal, neodymium glass, ruby and gas Co2And so on.
The total reflection mirror (2) and the output mirror (3) form a resonant cavity. In fig. 1, two plane mirrors are assumed, and in fact, they may be any optical mirrors that can constitute a laser resonator. Such as spherical mirrors, nichol mirrors, corner mirrors, etc.
The pump power supply (4) can be continuously pumped or pulse pumped, depending on the laser material and its Q-switched mode. For example, acousto-optic Q-switching is mostly continuous pumping, while electro-optic Q-switching is always pulsed pumping, etc.
The Q-switching element (5) is a key device for completing the Q-switching action, and generally requires that the extinction ratio is high enough. Fig. 1 is only a schematic form, and the specific structure of the device depends on the adopted Q-switching form. For example, when electro-optic Q-switching is used, it is typically composed of a crystal and a (or a pair of) polarizers. The only requirement for the Q-switching device is that it must be a controllable active Q-switching element rather than a passive Q-switching element consisting of a saturable absorber.
The Q-switching control power supply (6) is matched with the Q-switching device (5). The required power supply output varies greatly for different forms of Q-switching. For electro-optical KD＊In order to achieve the best possible Q-switching performance, the power supply (6) of the P-Q switching device must be able to output the high-voltage square wave shown in (a) or (b) of fig. 2, and both the rising edge and the falling edge of the square wave should be as steep as possible (i.e., as close as possible to the ideal state shown by the dashed line). The rise after the Δ t interval is particularly important for the present invention, which directly affects the minimum value at which the pulse width can be compressed. For acousto-optic Q-switched devices, the output of the power supply (6) should have the waveform shown in fig. 2 (c), where the rising and falling edges of the envelope of the rf signal should also be as steep as possible, especially the rising edge. The frequency of the radio frequency signal is 40-100MH, and the pulse repetition frequency is 0-24 KHz. No matter the electro-optic Q-switching power supply or the acousto-optic Q-switching power supply, the delta t interval is required to be continuously, stably and adjustably. In fact, we adjust the Q pulse width by adjusting the magnitude of Δ t.
Fig. 2 shows an output waveform of the power supply 6 in fig. 1. Wherein (a) and (b) are output waveforms of electro-optic Q modulation, and (c) is output waveform of acousto-optic Q modulation.
Fig. 3 is a diagram of a general Q-switched laser pulse formation process. Where δ is the intra-cavity loss, Δ n is the inverse population density, φ is the intra-cavity oscillating photon population density, t1Is the half width of the leading edge of the laser pulse, t2Is the laser pulse trailing edge half width,. DELTA.no is the initial inversion particle number density,. DELTA.nthIs the threshold inversion population density.
FIG. 4 is a schematic diagram of a Q-switched laser pulse forming process according to the present invention. In the figure, the number of photons in the cavity is denseThe cavity loss delta is immediately restored to alpha when the degree reaches the maximum value2Thereby causing the trailing edge of the pulse to decay rapidly, with the dotted line representing the normal Q-switched pulse waveform.
FIG. 5 is a graph of Q pulse width modulation achieved by modulating the loss rate, where the solid line represents a high loss rate, α2＞α1Therefore, the trailing edge of the laser pulse indicated by the solid line in fig. 5 attenuates quickly.
Fig. 6 illustrates a method for adjusting the Q-switch on-time interval τ to adjust the Q-pulse width. Wherein the time interval τ is shown by the solid line1Less than the time interval tau indicated by the dotted line2I.e. tau2τ so that the pulses represented by the solid lines begin to decay earlier than those represented by the dashed lines, thus Δ t2＞△t1。
The above analysis shows that the trailing edge decay rate of the Q-switched giant pulse depends on the cavity loss. And the cavity loss depends on the loss ratio of the Q-switch. Therefore, the purpose of continuously adjusting the Q pulse width can be achieved by only properly adjusting the loss factor of the Q switch after being turned off again (actually, adjusting the corresponding voltage in fig. 2). As shown in fig. 5, the loss factor α2＞α1So Δ τ2＜△τ1. However, this adjustment method has the disadvantage that three voltage levels must be used, which complicates the design of the power supply because the loss factor of the Q-switch needs to be made as large as possible in order to close the cavity sufficiently at the start of pumping, and the loss factor needs to be adjustable when the Q-switch is turned back off. Therefore, the method shown in fig. 6 according to the present invention is simpler and more reliable, i.e. the time for the Q switch to be turned off again can be adjusted to achieve the purpose of compressing the pulse width (e.g. adjusting the time interval for the Q switch to be turned on in fig. 2). As long as the trailing edge of the normal Q-switched pulse is reduced to one-half after the Q-pulse reaches the peak value (i.e. t after the peak value in fig. 3)2In time), the Q-switch is turned off at any time during the period, so as to achieve the purpose of compressing the half width of the pulse, only to a different extent. Practice proves that the method is more reliable and simpler than the method for adjusting the loss rate alpha. As shown in figure 6 of the drawings,time interval t2＞t1Thereby obtaining Δ τ2>. DELTA.τ 1, it can be seen that a method of adjusting the Q-switch on-time interval to adjust the pulse width is feasible.
The specific implementation method of the invention is very simple, and any practical Q-switched laser can be directly adopted by proper adjustment.
From the above description, it can be seen that the only difference between the present invention and the conventional Q-switched laser is that the Q-switched power supply is turned on again after a period of time. In fact, any practical Q-switched laser should have such a function. Since it is known that any practical Q-switched laser must be reusable. Also with a certain repetition rate. For example, the repetition frequency of electro-optic Q-switch is 0-100 Hz, and the repetition frequency of acousto-optic Q-switch is 0-20 KHz. For this reason, the Q-switch of any practical Q-switched laser must be restored to a high loss off state after firing a pulse, otherwise, energy storage for the next pulse is not possible. However, the on-time of a conventional laser Q-switch is long enough to ensure that the entire Q-switched pulse is emitted unimpeded. In addition, the speed of recovering the high-loss off state of the general Q-switched power supply is relatively slow, because the ordinary Q-switched laser does not require the action to be fast enough, so that the practical application of the invention can be completed by properly adjusting the Q-switched power supply from the two aspects: the turn-on time interval of the Q switch is adjusted to be matched with the forming time of the Q laser pulse, and the speed of recovering the high loss of the Q switch is accelerated as much as possible. Any common Q-switched laser can adopt the invention as long as the two points are achieved. In fact, it is not difficult to improve any of the Q-switching schemes, and there are many schemes, and there is no specific pattern.
FIG. 7 is a schematic diagram of an acousto-optic Q-switched power supply for practical application. By adjusting W1The time for the Q switch to be closed again can be adjusted, and the power supply can be used for actually realizing the acousto-optic modulation of the pulse width of the QYAG laser from 200ns to 100nsThe method is continuously adjustable, and simultaneously ensures that the peak power is unchanged and the output transverse mode is unchanged.
Claims (4)
1. A method for adjusting Q-switched pulse waveform. When the pump of the Q-switched laser starts, the Q switch is closed, and when the energy storage in the laser medium reaches the maximum, the Q switch is opened. The invention is characterized in that the Q switch is closed again after the Q switch is opened and in the Q pulse output process, thereby changing the working state of the laser resonant cavity and adjusting the waveform of the Q pulse.
2. The method of claim 1, wherein: the moment when the Q switch is turned off again is when the Q pulse reaches the peak value, the Q switch is in the maximum possible off state again, and the waveform trailing edge of the Q pulse is attenuated rapidly, so that the width of the Q pulse is compressed.
3. The method of claims 1, 2, wherein: the decay rate of the trailing edge of the Q pulse can be adjusted by adjusting the loss factor of the Q switch after the Q switch is turned off again or by adjusting the time for turning off the Q switch again, so that the width of the Q pulse can be continuously adjusted.
4. The method of claim 1, wherein: and closing the Q switch before the peak value of the Q pulse reaches, so that the Q pulse cannot reach the peak power, and adjusting the maximum value which can be reached by the Q pulse by adjusting the time for re-closing the Q switch.
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| CN 87103899 CN1013329B (en) | 1987-05-27 | 1987-05-27 | Q-switched laser pulse waveform adjusting method |
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| CN 87103899 CN1013329B (en) | 1987-05-27 | 1987-05-27 | Q-switched laser pulse waveform adjusting method |
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| CN1013329B CN1013329B (en) | 1991-07-24 |
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Cited By (7)
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| CN102224337A (en) * | 2008-11-21 | 2011-10-19 | 罗伯特·博世有限公司 | Laser-induced spark ignition for an internal combustion engine |
| CN102430855A (en) * | 2011-09-21 | 2012-05-02 | 长春理工大学 | Energy time domain accumulating method for multiple laser pulse sequences |
| CN106992425A (en) * | 2017-06-12 | 2017-07-28 | 中国原子能科学研究院 | With pulse incoherent quasi-molecule laser source is induced from compression property without ladder |
| CN108155555A (en) * | 2016-12-04 | 2018-06-12 | 中国科学院大连化学物理研究所 | A kind of impulse type rubidium steam blue laser of adjustable pulse width |
| CN108963746A (en) * | 2017-05-24 | 2018-12-07 | 中国科学院理化技术研究所 | Laser using method, pulse width adjustable laser and using method thereof |
| CN111864517A (en) * | 2020-07-29 | 2020-10-30 | 中国科学院长春光学精密机械与物理研究所 | A kind of laser pulse waveform purification method and system |
| CN112271543A (en) * | 2020-09-29 | 2021-01-26 | 北京卓镭激光技术有限公司 | Active Q-switched laser and pulse width modulation method thereof |
-
1987
- 1987-05-27 CN CN 87103899 patent/CN1013329B/en not_active Expired
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102224337A (en) * | 2008-11-21 | 2011-10-19 | 罗伯特·博世有限公司 | Laser-induced spark ignition for an internal combustion engine |
| US8783221B2 (en) | 2008-11-21 | 2014-07-22 | Robert Bosch Gmbh | Laser-induced spark ignition for an internal combustion engine |
| CN102224337B (en) * | 2008-11-21 | 2016-03-16 | 罗伯特·博世有限公司 | For the spark ignition device of the induced with laser of internal-combustion engine |
| CN102430855A (en) * | 2011-09-21 | 2012-05-02 | 长春理工大学 | Energy time domain accumulating method for multiple laser pulse sequences |
| CN108155555A (en) * | 2016-12-04 | 2018-06-12 | 中国科学院大连化学物理研究所 | A kind of impulse type rubidium steam blue laser of adjustable pulse width |
| CN108155555B (en) * | 2016-12-04 | 2019-11-15 | 中国科学院大连化学物理研究所 | A Pulsed Rubidium Vapor Blue Laser with Adjustable Pulse Width |
| CN108963746A (en) * | 2017-05-24 | 2018-12-07 | 中国科学院理化技术研究所 | Laser using method, pulse width adjustable laser and using method thereof |
| CN108963746B (en) * | 2017-05-24 | 2020-06-26 | 中国科学院理化技术研究所 | Method of using laser, laser with adjustable pulse width and method of using the same |
| CN106992425A (en) * | 2017-06-12 | 2017-07-28 | 中国原子能科学研究院 | With pulse incoherent quasi-molecule laser source is induced from compression property without ladder |
| CN111864517A (en) * | 2020-07-29 | 2020-10-30 | 中国科学院长春光学精密机械与物理研究所 | A kind of laser pulse waveform purification method and system |
| CN112271543A (en) * | 2020-09-29 | 2021-01-26 | 北京卓镭激光技术有限公司 | Active Q-switched laser and pulse width modulation method thereof |
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| CN1013329B (en) | 1991-07-24 |
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