Overview of the Chinese DPSS laser 532nm
Recently, the Chinese have mastered the production of relatively powerful and inexpensive diode-pumped solid-state lasers ( DPSS ). Surely many would be interested to know what is inside them, what characteristics these lasers have and what the Chinese have saved on.
Under the cut - a review of such necessary things in every home as a one-watt green laser.
Before writing something, I want to emphasize in capital letters:
')
In this review there will be no video of how the laser sets fire to matches, bursts balls, etc .: such in bulk and on Youtube. Instead, we will check the compliance of the declared characteristics with the real one, and, of course, we will consider the construction of this device - the obligatory dose of geek porn is provided.
The laser was manufactured by CST (whose products are considered somewhat higher quality than DHOM products) by order of UltraLasers, Inc. It belongs to the highest class IV laser hazard , i.e. in addition to protection (glasses), when working with it, it is necessary to use a radiation absorbing trap, and also to always secure the radiator so that the touched wire does not turn the head in an unknown direction.
Let's go through the characteristics in order.
FAIL. From the aperture shines not only 532nm (green), but also 808nm and 1064nm (invisible infrared). And it shines in such a way that it cannot be ignored. Infrared filter in the laser is not put.
TRUE. Full output power at all wavelengths passes for 2.5W. The yield of useful green is about 1.8W , which also significantly exceeds the declared power - this is a characteristic feature of all Chinese lasers of this type.
It follows from the measurements that the invisible infrared part of the radiation accounts for about 700 milliwatts, which are much easier to get into the unprotected eye than it seems (see the next paragraph).
FAIL. The measured discrepancy for 532 nm was 2.3 mrad. For 808nm, it is an order of magnitude larger, approximately 30 mrad. It looks like this:
Violet is IR. Pay attention to the relative brightness of the IR and green. The diameter of the green beam corresponds to the white spot in the photograph, the green border is already scattering from the surface.
Thus, holding the head near the green beam (when adjusting the optics, etc.) there is a considerable chance to get under the beam of IR, which freely passes through glasses that protect against 532nm, and bring a lot of joy to ophthalmologists. Therefore, once again:
Be sure to install an infrared filter!
TRUE. And there is.
FAIL. The low-order Gauss-Laguerre mode is obtained only with absolutely insignificant power (less than 50 mW). Above this threshold we have something like this:
Already not TEM 10 , but also not TEM 11 . This is quite typical: with such a resonator and power, it is difficult to avoid amplification of higher-order modes.
FAIL. For testing, I gathered on my knee a simple TTL PWM at 26 kHz (Attention, a fatal number! Without microcontrollers and FPGA!) Of the available components (comparator LM339 plus strapping):
And with a different duty cycle I got oscillograms on a photodiode:
25%
50%
75%
From the input rectangular TTL there is little left. The spectrum of the same signal, as expected, is replete with harmonics:
TRUE. And Peltier and the fan are present. In the process, the emitter housing practically does not heat up.
When working with DPSS lasers, it is useful to have an infrared sight. The most affordable option is to buy a cheap digital soap dish and extract an infrared filter from it. As a result, instead of one useless thing, we get two useful ones: an IR camera and a filter. I take IR photographs with an Olympus VG-150, which cost me less than 2,000 rubles, including delivery. In addition, the filter in it is not glued to the matrix, but simply lies on it, pinned by an elastic band, and removed without difficulty and damage in two minutes.
The same filter can also be used for a laser: the maximum transmittance is just in the green area. But I do not recommend fixing it directly to the outlet (even from the inside) - the light scattered on the filter is enough to blindly unpleasantly.
At the BP there are:
Here the Chinese planted a pig : the laser was turned on with an unlocked lock and an untapped key, just when the button was clicked behind! This is a gross violation of TB when you first turned on very, hmm, surprised. At the same time, I checked the “Stop” button.
Opening the unit showed that, for the convenience of the user, the connectors of the key and the locking are closed by “snot” on the back side of the board, and the switch with the key is not connected at all:
Structurally, the unit consists of two modules: a switching power supply for voltages of 5 and 12 volts and a diode driver combined with a regulator for two thermoelements.
It consists of two identical sources in one case: the first is 12V 6.5A, the second is adjustable 4.6–6.3V 6.5A. Do not be confused by the identical colors of the wires: the upper red is 5V and the lower red is 12V.
No different design sophistication:
Three linear current stabilizers on the LM358 op-amp and output stages on the IRF530N (MOSFETs on the back side of the board) - for the laser diode and two thermoelements. Thermocouple is used only one. The upper left chip is the 74LS00, it turns on the laser on condition of a high level on the TTL modulation connector, matching the temperature of the sensors with the expected and triggering of a five-second delay timer assembled on the NE555 chip (bottom left). All other chips - LM358.
The leftmost resistor controls the current of the laser. Large resistors are used as current-measuring shunts. MOSFETs are bolted to a massive radiator the size of an entire driver board. The laser current stabilizer is powered by + 5V, and thermoelements - from + 12V.
The quality of the soldering is average, with traces of manual refinement by the file. They saved on filter elements, otherwise there is no particular crime.
The laser current is set to 5.4A, which suggests that the working fluid is pumped by a five-watt IR laser diode. The absence of the second thermoelement means that the KTP crystal is not heated, and therefore may not work optimally, which shortens its service life.
Perhaps the only thing that corresponds to the specifications in this laser is power. But it was given with a margin. The expected period of work also inspires doubts, but this will become clear when disassembling the radiator. This review and so it turned out quite voluminous, t.ch. I will carry out the description of the design of the laser itself in the second part.
This laser is very dangerous: not only does the 700 MW infrared light shine, it also turns on unexpectedly. However, both are simply eliminated. Directly from the Chinese on Aliexpress at the time of this writing, such a laser could be bought for $ 650, not including shipping.
Thanks to everyone who read to this place!
Under the cut - a review of such necessary things in every home as a one-watt green laser.
Before writing something, I want to emphasize in capital letters:
when working with such lasers need protection!
At least you need glasses that protect from 808nm and from 532nm. Next, I will show why this is so important.')
In this review there will be no video of how the laser sets fire to matches, bursts balls, etc .: such in bulk and on Youtube. Instead, we will check the compliance of the declared characteristics with the real one, and, of course, we will consider the construction of this device - the obligatory dose of geek porn is provided.
Main characteristics
| Wavelength (nm) | 532 |
| Output Power (mW) | > 1000 |
| Divergence, Full angle (mrad) | 2.0 |
| Beam Diameter at the Aperture (mm) | ~ 2.5 |
| Transverse mode | TEM 00 |
| Modulation mode | TTL up to 30kHz |
| Cooling mode | TEC & Air |
| Expected Lifetime (hours) | 10,000 |
Let's go through the characteristics in order.
Wavelength: 532nm
FAIL. From the aperture shines not only 532nm (green), but also 808nm and 1064nm (invisible infrared). And it shines in such a way that it cannot be ignored. Infrared filter in the laser is not put.
Output Power:> 1W
TRUE. Full output power at all wavelengths passes for 2.5W. The yield of useful green is about 1.8W , which also significantly exceeds the declared power - this is a characteristic feature of all Chinese lasers of this type.
It follows from the measurements that the invisible infrared part of the radiation accounts for about 700 milliwatts, which are much easier to get into the unprotected eye than it seems (see the next paragraph).
Beam divergence: 2 mrad
FAIL. The measured discrepancy for 532 nm was 2.3 mrad. For 808nm, it is an order of magnitude larger, approximately 30 mrad. It looks like this:
Violet is IR. Pay attention to the relative brightness of the IR and green. The diameter of the green beam corresponds to the white spot in the photograph, the green border is already scattering from the surface.
Thus, holding the head near the green beam (when adjusting the optics, etc.) there is a considerable chance to get under the beam of IR, which freely passes through glasses that protect against 532nm, and bring a lot of joy to ophthalmologists. Therefore, once again:
Be sure to install an infrared filter!
Beam diameter at aperture: ~ 2.5mm
TRUE. And there is.
Transverse fashion: TEM 00
FAIL. The low-order Gauss-Laguerre mode is obtained only with absolutely insignificant power (less than 50 mW). Above this threshold we have something like this:
Already not TEM 10 , but also not TEM 11 . This is quite typical: with such a resonator and power, it is difficult to avoid amplification of higher-order modes.
Modulation: up to 30 kHz TTL
FAIL. For testing, I gathered on my knee a simple TTL PWM at 26 kHz (Attention, a fatal number! Without microcontrollers and FPGA!) Of the available components (comparator LM339 plus strapping):
And with a different duty cycle I got oscillograms on a photodiode:
25%
50%
75%
From the input rectangular TTL there is little left. The spectrum of the same signal, as expected, is replete with harmonics:
Cooling: Peltier element with fan
TRUE. And Peltier and the fan are present. In the process, the emitter housing practically does not heat up.
Useful tool
When working with DPSS lasers, it is useful to have an infrared sight. The most affordable option is to buy a cheap digital soap dish and extract an infrared filter from it. As a result, instead of one useless thing, we get two useful ones: an IR camera and a filter. I take IR photographs with an Olympus VG-150, which cost me less than 2,000 rubles, including delivery. In addition, the filter in it is not glued to the matrix, but simply lies on it, pinned by an elastic band, and removed without difficulty and damage in two minutes.
The same filter can also be used for a laser: the maximum transmittance is just in the green area. But I do not recommend fixing it directly to the outlet (even from the inside) - the light scattered on the filter is enough to blindly unpleasantly.
Go to geek porn
Power Supply
 |  |
At the BP there are:
- Interlock connector - contacts must be closed for the laser to work
- Wire sticking out of a hole Trigger - TTL modulation, active level - low
- Power switch on the back of the unit
- Stop button - emergency shutdown (requirement for hazard class IV)
- Key switch - laser start (requirements for hazard class)
- Three indicators: power, radiation and error, respectively
- Laser connector, pinout is as follows:
1. TEC +
2. LD +
3. LD-
4. Thermal Sensor
5. Thermal Sensor
6. Fan +
7. TEC-
8. Fan-
Here the Chinese planted a pig : the laser was turned on with an unlocked lock and an untapped key, just when the button was clicked behind! This is a gross violation of TB when you first turned on very, hmm, surprised. At the same time, I checked the “Stop” button.
Opening the unit showed that, for the convenience of the user, the connectors of the key and the locking are closed by “snot” on the back side of the board, and the switch with the key is not connected at all:
Structurally, the unit consists of two modules: a switching power supply for voltages of 5 and 12 volts and a diode driver combined with a regulator for two thermoelements.
Pulse source
It consists of two identical sources in one case: the first is 12V 6.5A, the second is adjustable 4.6–6.3V 6.5A. Do not be confused by the identical colors of the wires: the upper red is 5V and the lower red is 12V.
Driver
No different design sophistication:
Three linear current stabilizers on the LM358 op-amp and output stages on the IRF530N (MOSFETs on the back side of the board) - for the laser diode and two thermoelements. Thermocouple is used only one. The upper left chip is the 74LS00, it turns on the laser on condition of a high level on the TTL modulation connector, matching the temperature of the sensors with the expected and triggering of a five-second delay timer assembled on the NE555 chip (bottom left). All other chips - LM358.
The leftmost resistor controls the current of the laser. Large resistors are used as current-measuring shunts. MOSFETs are bolted to a massive radiator the size of an entire driver board. The laser current stabilizer is powered by + 5V, and thermoelements - from + 12V.
The quality of the soldering is average, with traces of manual refinement by the file. They saved on filter elements, otherwise there is no particular crime.
The laser current is set to 5.4A, which suggests that the working fluid is pumped by a five-watt IR laser diode. The absence of the second thermoelement means that the KTP crystal is not heated, and therefore may not work optimally, which shortens its service life.
Conclusion
Perhaps the only thing that corresponds to the specifications in this laser is power. But it was given with a margin. The expected period of work also inspires doubts, but this will become clear when disassembling the radiator. This review and so it turned out quite voluminous, t.ch. I will carry out the description of the design of the laser itself in the second part.
This laser is very dangerous: not only does the 700 MW infrared light shine, it also turns on unexpectedly. However, both are simply eliminated. Directly from the Chinese on Aliexpress at the time of this writing, such a laser could be bought for $ 650, not including shipping.
Thanks to everyone who read to this place!
Source: https://habr.com/ru/post/187988/
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