Researchers at the University of California–Los Angeles (UCLA) and the University of Göttingen (Göttingen, Germany) have used a unique high-speed measurement technique to demonstrate that patterns that develop in ultrafast laser pulses mimic wave patterns found in nature. Not otherwise discernible with conventional ensemble measurement methods, the patterns were seen by analyzing single-shot spectra of “modulation instability”—a nonlinear interaction that leads to pattern formations in nature such as sand ripples, water waves, and heart rhythms—produced by ultrashort laser pulses in optical fibers.
In the experiment, 1550 nm, 25 MHz repetition-rate, 3 ps pulse-duration laser pulses are injected into a nonlinear optical fiber to create spontaneously growing oscillations (frequency modes) that are then captured by stretching the output in a spool of dispersive fiber to record the subnanometer optical spectrum of each pulse. Statistical analysis of the thousands of individual pulses allows the researchers to identify an interactive effect between the frequency modes: within a pulse, overlapping modes at similar frequencies either unite or suppress each other, leaving only one to dominate in the end. Conventional time-averaged measurement records spectrally broad modulation-instability sidebands (well-known in nonlinear optics), hiding the interactive effect between the underlying discrete modes. Their observations suggest that similar interactions may be at work in other physical contexts (for example, sand undulations) in which single temporal or spatial patterns become dominant. Contact Daniel Solli at [email protected].
