Liquid Crystals Could Help Protect Against Laser Pointer Attacks

Liquid crystals could someday be used to help deflect laser pointer attacks on aircraft, regardless of the wavelength used in the attack.

According to the Federal Aviation Administration, 6,754 laser strikes on aircraft were reported in 2017. The unexpected flash of intense light from even a low-tech boardroom laser pointer can distract pilots and, depending on the wavelength and intensity of the laser, can cause visual damage.

Liquid crystals sandwiched between two 1-inch squares of glass scatter green and blue light on a wall when the cells are triggered by laser illumination (right panels). Courtesy of Daniel Maurer.

To shield pilots from laser attacks, the research team from Lewis University took advantage of the polarization and absorbance properties of liquid crystal (LC) technology. The team placed a solution of LCs called N-(4-methoxybenzylidene)-4-butylaniline, or MBBA, between two 1-inch-square panes of glass. “We wanted to come up with a solution that didn’t require us to completely re-engineer an aircraft’s windshield, but instead adds a layer to the glass that harnesses the existing power system for windshield defrosting,” said researcher Daniel Maurer.

MBBA has a transparent liquid phase and an opaque crystalline phase that scatters light. By applying a voltage to the apparatus, the researchers caused the crystals to align with the electrical field and undergo a phase change to the more solid crystalline state. As laser light permeates the LC, its power is reduced via the following dissipation pathways: absorption of the laser’s energy; scattering of the laser light when in crystal phase; and its interaction with linearly polarized light. If polarization of the laser and LC are parallel, the LC relies on the ability to reflect light in crystal phase. If these polarizations are perpendicular, roughly 90 percent of the laser’s power is blocked regardless of wavelength. The LCs demonstrated the ability to block lasers of different powers, simulating various distances of illumination, as well as light shone at different angles onto the glass.

In addition, the system was shown to be fully automatic: A photoresistor detected laser light and then triggered the power system to apply the voltage. When the beam was removed, the system turned off the power, and the liquid crystals returned to their transparent, liquid state. “We only want to block the spot where the laser is hitting the windshield and then have it quickly go back to normal after the laser is gone,” said professor Jason Keleher. The rest of the windshield, which was not hit by the laser, would remain transparent at all times.

Now that the researchers have shown that their approach works, they plan to scale it up from 1-inch squares to the size of an entire aircraft windshield. Initial results have shown that a sensor grid pattern on 2-inch squares of glass will respond only to the section of glass that is illuminated. The team is also testing different types of liquid crystals to find even more efficient and versatile ones that return to the transparent state more quickly once the laser is removed.

The researchers presented their results at the American Chemical Society (ACS) Spring 2019 National Meeting & Exposition, March 31-April 4, 2019, Orlando, Fl.