Quarton VLM-520-03-LPT oscillating optical output

Support Q&A
1

Hi,

I am currently using a Quarton VLM-520-03-LPT 520 nm laser module purchased/listed through DigiKey, and I am observing an unexpected oscillatory output behavior. I am hoping you can help determine whether this is a known behavior for this module, and whether there are recommended steps or alternative laser modules that would provide a more stable CW output.

Product:

  • Wavelength: 520 nm

  • Rated optical power: 1 mW

  • Specified input voltage: 7–10 V

  • Current rating: 80 mA

  • Operation: CW laser module

Experimental setup:

  • The laser is powered using a DC bench supply.

  • The laser beam is coupled through a Thorlabs fiber/collimator setup and measured using a Thorlabs PM100D power meter with an S120VC photodiode sensor.

  • Measurements were performed in a dark room to minimize ambient light.

  • The PM100D line filter was set to 60 Hz.

  • No external triggering was used.

Observed behavior:

  • The 520 nm laser output shows a repeating sawtooth-like oscillation in optical power over time.

  • The measured power at the sensor oscillates approximately between about 1.4 µW and 2.1 µW after the fiber/collimator setup.

  • The oscillation appears visually to be on the order of roughly 1–2 Hz based on the power meter graph.

  • We tested the setup and determined that the oscillation appears to originate from the laser module itself rather than from the Thorlabs power meter, sensor, fiber coupling, or ambient light.

We are wondering whether the VLM-520-03-LPT laser module has known output instability, thermal cycling, internal driver regulation behavior, or sawtooth-like power fluctuations, especially when operated near the lower end of its specified voltage range.

Could you advise on the following?

  1. Has DigiKey or Quarton seen this type of oscillatory output behavior with the VLM-520-03-LPT?

  2. Are there recommended operating conditions, such as supply voltage, current limit, warm-up time, or filtering, to reduce or eliminate this oscillation?

  3. Could the internal driver electronics in the module produce this type of sawtooth-like power modulation?

  4. Would operating the module closer to the middle of the specified 7–10 V range improve stability?

  5. Is there another 520 nm laser module you would recommend for more stable CW optical output?

  6. Are there any datasheets, application notes, or stability specifications available for this module?

Please let me know if it would be helpful for me to send photos of the setup, screenshots of the oscillation on the power meter, or additional power supply settings.

Thank you for your help.

Best regards,

Oscilation from powermeter.pdf (321.5 KB)

2

Hi andrew-alatorre2005,

Welcome to the TechForum.

To start out, I have no information regarding the internal driver circuitry of the VLM-520-03-LPT. I do note that in the datasheet, it represents itself as follows:

“Economical Green Dot Laser Module - Low cost solution for consumer grade positioning, measuring, pointing and laser sighting device.”

This implies that it is probably not suitable for scientific applications requiring tight output control.

Basically, it is intended to just be used in pointing applications, and because of this, it’s unlikely that our customers would have even noticed the behavior you describe if it were happening.

That being said, it might be informative to take a look on a scope at the current draw of the module as well.

We have not tested for it and were not specifically aware of this behavior, but as mentioned above, for the expected use case, this would typically not be an issue.

I suspect that allowing it to warm up for some time might help stabilize it a bit more, and running it from 8.5V~9.5V would seem optimal, but it’s unlikely to eliminate it the oscillations. Based on your description of the behavior while using a bench-top supply, I would be a little surprised if current limiting or filtering would help significantly.

It seems a little unusual, but depending on the architecture of the design, it’s quite plausible, particularly considering the typical use-case for the module.

I do note from the datasheet that its ambient operating temperature is limited to 30°C, so it would not be hard to get it outside of its optimal temperature range with undefined results.

Also, note that it states in the specifications table on page 2 of the datasheet that the case is tied to the positive supply rail of the module, so if it is not mounted in an isolated holder, that could have less than ideal effects on it’s behavior.

See answer for #2 above.

I have not found any green laser modules we carry with integrated driver circuitry which specifically state a stable CW output in their documentation.

The VLM-520-01 LPT is described in its datasheet as an “Industrial” grade product. It has a wider operating temperature range, has a higher ESD rating, and includes reversed supply circuit protection, over current protection, and surge protection. Even so, it is still primarily intended for precision pointing applications, so having a very steady drive current level may not be prioritized in its design.

One other possible option does seem more likely to meet your needs, though in a much higher price range, would be the VLM-520-96 LPA. This one is designed more for lab and medical research and physical-optic experiment applications. It has a built-in trimmer for power adjustment as well as a lens focus adjustment capability. This one states the following in the datasheet:

The laser output power can be adjusted using a built in precision trimmer, which ranges
from 0 t o 4 .25 0. 2 5 mW, and remains compliant with class 3R safety regulations. This
versatile tool is a must have for medical and laboratory research, as well as physical
optic experiments, providing exceptional control and reliability.

Under “Specifications” for the VLM-520-96 LPA it does state the following:

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