Chapter 5 Explanation of Laser Parameters
5.1 Introduction to common lasers
The following is based on the personal experience of using the laser. There may be some errors. Just for reference, do not believe. In general, lasers are differentiated according to the wavelength of the laser. There are four types of lasers: ① 1024nm laser, also called fiber laser; ② 355nm laser, commonly called ultraviolet laser; ③ 532nm laser, commonly called green laser; ④ 10240nm Laser, also called CO2 laser
5.1.1 Fiber Laser
At present, fiber lasers are more commonly used in the market. Common brands include IPG, SPI, JPT, Ruike, and Han's MP lasers. We will not mention performance in terms of performance. They can be divided into two categories based on energy control methods
The first type is IPG, JPT, Ruike, and Han MP lasers. The energy of these manufacturers' lasers is controlled digitally, and the 8 pins are controlled together, that is, all 8 pins represent 100% energy at all high levels and 0% energy at all low levels. We can understand that the eight pins are a binary number, 11111111 binary, and 255 decimal, which is also 100% energy. Binary 01111111, decimal 127, which is about 50% energy. 0 means low level and 1 means high level. It can also be understood as follows: Set the TTL signals of PIN1 ~ 8, and set the current of the pump laser diode through the combination of TTL signals, that is, the output power of the laser. Codes in the range of 0 ~ 255 can be set through PIN1 ~ 8, corresponding to 0% ~ 100% power output (the actual optical power output may not be in a linear relationship with these settings)
其中大族MP激光器、JPT激光器，是可以设置脉宽值（单位ns，与Q脉宽是两个概念），在不同的脉宽之下，同样的频率功率，打出来的能量会有差异，一般调节工艺时会需要用到，UDM_SetPulseWidth(unsigned int uPulseWidth)函数可以改变激光器脉宽值。下图为JPT激光器说明说上关于脉宽的截图：
Among them, MP lasers and JPT lasers can set the pulse width value (unit ns, and Q pulse width are two concepts). Under different pulse widths, the same frequency power will produce different energy. Generally It will be used when adjusting the process. The UDM_SetPulseWidth (unsigned int uPulseWidth) function can change the laser pulse width value. The picture below is a screenshot of the pulse width of the JPT laser description.
The second type is SPI laser, whose energy control is controlled by analog, 0 ~ 10V represents 0% ~ 100% energy.
There is a concept on the SPI laser called a waveform, which is equivalent to adjusting the pulse width. The SPI laser defines 64 types of waveforms, 0 to 63, which can be set by the following figure
In order to control the above lasers, in addition to energy, a laserEnable signal (also called MO), a laserOn signal (also called PA), and a frequency signal are required. These signals are indispensable.
5.1.2 UV, CO2, green laser
Compared to fiber lasers, these three types of lasers are relatively simple to control. Generally, only a Q-frequency signal is needed to control the switching light. The energy is determined by the duty cycle (duty cycle = pulse width / period). ). When encountering such a laser, you need to set the non-light-emitting Q frequency and the non-light-emitting Q pulse width to 0, otherwise the laser will always emit light and cannot be turned off. The CO2 laser burns your skin, so be careful.
5.1.3 About the laser frequency
Like a fiber laser, to control its light output, it needs more than a dozen signals, and all of the signals can be output. Therefore, its non-light Q frequency and non-light Q pulse width can be set to 0. The non-exit Q frequency is equal to the output Q frequency, and the non-exit Q pulse width is equal to the output Q pulse width.
Note: If the Q-frequency pulse width is not set to 0 forcibly, for some lasers with poor performance, the response will be slower, which will cause abnormal starting frequency, laser dot spacing and dot energy. It is recommended to set the same. To avoid this phenomenon. In addition, the duty cycle is preferably 0.5, which means that the Q pulse width is half of the Q period.
Like CO2, UV, green, and other lasers, it only needs one Q frequency and Q pulse width signal. Therefore, the non-lighting Q frequency and non-lighting Q pulse width must be set to 0, otherwise the laser cannot be turned off. Of course, in addition to this signal, some manufacturers' lasers may also require a laseron signal. At this time, it does not matter if it is set to 0.
5.2 Description of laser units
When assigning values to laser parameters in DEMO, there is a * 100 operation, as shown in the figure below:
The reason for this is that the unit accepted by the laser is 10ns, that is, the minimum control period is 10ns, so the unit in the structure is also 10ns by default. However, in laser processing, it is customary to use us as the unit, so the unit time of the us input on the interface must be converted into 10ns as the unit. For example, if you enter 10us, it will be converted into 10ns. The final value is 10 * 100, which is 1000 10ns. If the user enters 50us, the final value is 50 * 100 10ns, and so on.
5.3 About the concepts of Q frequency, Q pulse width, and Q period
The Q period (T) and the Q frequency (F) have an inverse relationship, that is, T = 1 / F. The period unit is seconds (S) and the frequency unit is hertz (HZ). Usually in the laser industry, the Q frequency is generally used as the unit, and the Q period is not used. Therefore, after the user inputs the frequency on the interface, it needs to be converted to the Q period for the control card.
If the user inputs a frequency of 20K, the corresponding Q period is 1 / 20K = 0.00005s = 0.05ms = 50us, and 50us needs to be converted into a unit of 10ns and sent to the control card. It needs to be explained that Q period ≥ Q pulse width, otherwise the relationship does not hold.
The user can also define a variable based on this, called the duty cycle. This can be simplified to this formula:
Assume that the user input frequency is frequency (KHz) and the duty cycle is dutyCycle (0 ~ 100%).
那么QPeriod(周期)= (int)(100000 / frequency);此值已经转成了10ns的单位
QWidth = QPeriod * dutyCycle = (int)(100000 * dutyCycle / frequency)；此值已经转成了10ns的单位
Then QPeriod (period) = (int) (100000 / frequency); this value has been converted into units of 10ns
QWidth = QPeriod * dutyCycle = (int) (100000 * dutyCycle / frequency); this value has been converted into units of 10ns
Assign these two values directly to the relevant variables in the structure
If it is a fiber laser, the duty cycle dutyCycle is recommended to be 50%.
If it is a CO2 laser, its energy is determined by the duty cycle. Therefore, it is recommended to assign the energy percentage on the interface to the duty cycle. If the user inputs 50% energy, dutyCycle = 50%.