DIY Laser Scanning Microscope Built Using an Old Blu-ray Laser

Optical microscopes are great for getting a nice, clear visuals of small objects. But they do have a bottom limit where objects are too small for an optical microscope to resolve differences between features. Laser scanning microscopes can make out more detail by only resolving a single point at a time to remove interference. Hobbyists and citizen scientists rarely have access to laser scanning microscopes, as they start at several thousand dollars and go up to many tens of thousands of dollars. That’s why it is so impressive that Doctor Volt was able to make his own laser scanning microscope using an old Blu-ray laser.

You can probably find an old Blu-ray drive or player at your local thrift store for a few bucks, or even for free in an e-waste bin. A Blu-ray drive uses a laser diode to project a laser beam onto the disc, which will either reflect well or not depending on the bit at that location. A sensor detects the reflection and the system returns a one or zero based on a set threshold. But the sensor itself isn’t binary — it measure the intensity of the reflected light. By running that same process and recording each intensity measurement, one can create an image of the surface of whatever the laser scans. The resolution is a function of the physical movement of the laser as it scans.

Doctor Volt was able to do this affordably by utilizing as many of the parts from the original Blu-ray drive as possible. Those parts included the laser diode, the focus coil, the sensor, the frame, the stepper motor that moves the laser, and its lead screws. An ESP32 development board controls the X and Y axes through motor drivers (one for the stepper, one for the scanning electromagnet). It also controls the laser diode with a voltage regulator and the focus coil with a transistor. Finally, it monitors the output from the sensor through an op-amp that increases the signal enough for the ESP32’s analog input pin.

The ESP32 handles the low-level control of laser scanning, but a computer interprets everything and hosts the custom interface. That interface has adjustments for contrast, brightness, focus, and scan speed. The latter two settings need to be set before scanning, but the user can adjust the brightness and contrast after scanning to get a clear picture. The scanning results show up as an image in the interface line-by-line as the laser moves across the object’s surface.

The magnification power and fidelity of this DIY microscope aren’t as good as from a commercial laser scanning microscope, but they’re still very impressive. After replacing the original lead screw with a model that has a finer pitch, Doctor Volt was able to get some very good results that exceed those of hobbyist optical microscopes on the market.