![]() You can also do the same thing with light, but it is harder, to coherently beam steer the light from coupled laser emitters is an active area of research. The more elements you have typically the more directional you can make the beam. However, you can do the same thing with light it is just harder engineering.įor radar you can do beam steering by controlling the relative phase between antenna elements. With radio waves, since the wavelength is longer and the signal typically has more coherence it is easier to make arrays of antenna dishes and end up with an effective larger aperture. In general for either light or radio wave radars and communication systems the size of transmitters/receivers telescopes or antenna that ultimately determine the amount of energy that hits the target and then how much gets received. This is partly because of spectrum allocation but light can have higher bandwidth, and rather than large antennas can be smaller packages. This is hard to explain in a couple of sentences, but this can be used for communications, quantum cryptography, and with some creative license can be applied in a hard science kind of way for your application of sensing other spacecraft or other applications.Īs an aside, many of the LEO satellites and probably others that are being networked together are probably going to be communication via light as an alternative to radio waves. When the photons are "entangled" when something happens to one photon, it can be observed by measuring the other photon. There are a bunch of games that can be played to discriminate you photons from others since you know the wavelength, polarization, timing of the signal and other things about your photons.Īn emerging real technology is the use of quantum mechanics to have entangled photons. ![]() So, you don't absolutely have to have a lot of light return especially if you have some other information to tell that it is your photons and not some other source of photons. The amount of energy in a visible photon is a couple of electron volts, whereas a radio wavelength photons is a few milli electron volts. So for the big distances of deep space that probably determines how many photons hit your target per laser pulse.Īnother nice thing about light is that you can have detectors that can detect single photons. This means that the laser beam is much much more directional than the radar, but far from the laser you can figure out what the radius of the spot size is by taking the angle in radians and multiplying it by the distance. Where $w$ is what is called the beam waist of the beam, and is often the aperture size of the laser, although one can also put the beam waist somewhere in front of the laser depending on the lens design. The formula for $\theta$, the half angle of how the beam is expanding, is This is because the wavelength of light is much smaller than that of radio waves. Maybe the most important for this question is that you can have a diffraction limited beam. There are several nice things about light compared to radar.
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