New research published in the acclaimed journal Nature Physics reports that researchers from Utrecht University in the Netherlands and TU Wien in Vienna, Austria, have shown it is possible to optimize the information gathered from a laser beam in complex, disordered environments. While lasers are useful for measuring an object's position or velocity in non-complex environments with direct, unobstructed views of said object, in complex or irregular environments like those in the human body, the usefulness of laser beams is limited because of light scattering and refraction. Now the researchers present a new technology that can modify a laser beam to deliver precise information even in irregular environments.
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The new technology has the potential to improve the effectiveness of lasers in a variety of different fields of application, including microbiology and the production of computer chips. Stefan Rotter from TU Wien explains: "You always want to achieve the best possible measurement accuracy - that's a central element of all natural sciences. Let's think, for example, of the huge LIGO facility, which is being used to detect gravitational waves: There, you send laser beams onto a mirror, and changes in the distance between the laser and the mirror are measured with extreme precision." In this scenario, all disturbances are carefully avoided, but, points out Rotter, such sterility isn’t always possible.
"Let's imagine a panel of glass that is not perfectly transparent, but rough and unpolished like a bathroom window," says Allard Mosk from Utrecht University. "Light can pass through, but not in a straight line. The light waves are altered and scattered, so we can't accurately see an object on the other side of the window with the naked eye." Mosk alludes that this is how we can think of a laser beam entering biological tissue, full of little irregularities that disturb a straight laser beam and scatter its light. In this situation, getting the desired information with a straight laser beam is extremely challenging.
But – thought the researchers – what if it were possible to predict the ways in which a complicated environment would impact a laser beam and purposely create a complicated wave pattern (instead of a straight wave pattern) that could twist and turn around the environmental disturbances as still arrive to the desired location?
"To achieve this, you don't even need to know exactly what the disturbances are," elaborates first author Dorian Bouchet. "It's enough to first send a set of trial waves through the system to study how they are changed by the system. You can show that for various measurements there are certain waves that deliver a maximum of information as, e.g., on the spatial coordinates at which a certain object is located."
The experiments that the physicists carried out showed that their mathematical procedure is in fact capable of calculating optimal waves of this sort. "We see that the precision of our method is only limited by the so-called quantum noise," notes Allard Mosk. "This noise results from the fact that light consists of photons - nothing can be done about that. But within the limits of what quantum physics allows us to do for a coherent laser beam, we can actually calculate the optimal waves to measure different things. Not only the position but also the movement or the direction of rotation of objects."