3 ms·

>"But the new laser beams don’t follow this basic law of light. And it’s not just Snell’s Law either – the team says they also ignore Fermat’s Principle, which

>"But the new laser beams don’t follow this basic law of light. And it’s not just Snell’s Law either – the team says they also ignore Fermat’s Principle, which says that light always takes the shortest possible path. “This new class of laser beams has unique properties that are not shared by common laser beams,” says Ayman Abouraddy, principal investigator of the study. “Spacetime wave packets can be arranged to behave in the usual manner, to not change speed at all, or even to anomalously speed up in denser materials. As such, these pulses of light can arrive at different points in space at the same time.” PDS: Or, quite possibly the same point in space at different times (think out-of-order as a possibility, since different points in space at the same time would imply this to be true as well...) [...] >"That’s because they’re not messing with the oscillations of the light waves themselves – instead, they’re controlling the speeds at which the peaks of the light pulses travel. This is done using a device called a spatial light modulator, which reorganizes the energy of each pulse of light to intertwine its properties in space and time." "“Space-time refraction defies our expectations derived from Fermat’s principle and offers new opportunities for molding the flow of light and other wave phenomena,” says Basanta Bhaduri, co-author of the study."

pharke 6y ago
I wonder if some combination of different materials and different modulations could allow these pulses to arrive at the same point at the same time? If so, how much could you scale that and would it be more useful than just building a higher powered laser?
- jlokier 6y ago
  That's more or less how an ultrashort pulse laser works already. Different wavelengths (colors) take different paths so the high energy of the pulse is spread out for processing over different parts of the optical components. The spreading is obvious in space. Less obvious is that this also spreads it in time, because each region of space gets a narrower frequency range than if the different wavelengths weren't taking different paths, and a narrower frequency range corresponds directly to a longer timescale for the pulse (see Fourier transforms). Then the different wavelengths are focused back together to a small spot. This obviously focuses them in space. Their path lengths are arranged carefully so they also arrive in just the right relative phase, and this causes the longer pulses at each narrower frequency to combine into a short pulse at a broad range of frequencies. The careful attention to relative phase is literally focusing the pulse in time as well as space, to make an ultrashort pulse. The current record for "most focused in time" pulse is 43 attoseconds, which is 43 nano-nanoseconds, 43 micro-micro-microseconds, and 43 milli-milli-milli-milli-milli-milliseconds. It uses this technique.

pharke 6y ago

I wonder if some combination of different materials and different modulations could allow these pulses to arrive at the same point at the same time? If so, how much could you scale that and would it be more useful than just building a higher powered laser?

jlokier 6y ago
That's more or less how an ultrashort pulse laser works already. Different wavelengths (colors) take different paths so the high energy of the pulse is spread out for processing over different parts of the optical components. The spreading is obvious in space. Less obvious is that this also spreads it in time, because each region of space gets a narrower frequency range than if the different wavelengths weren't taking different paths, and a narrower frequency range corresponds directly to a longer timescale for the pulse (see Fourier transforms). Then the different wavelengths are focused back together to a small spot. This obviously focuses them in space. Their path lengths are arranged carefully so they also arrive in just the right relative phase, and this causes the longer pulses at each narrower frequency to combine into a short pulse at a broad range of frequencies. The careful attention to relative phase is literally focusing the pulse in time as well as space, to make an ultrashort pulse. The current record for "most focused in time" pulse is 43 attoseconds, which is 43 nano-nanoseconds, 43 micro-micro-microseconds, and 43 milli-milli-milli-milli-milli-milliseconds. It uses this technique.