I work in the life sciences but use lasers in many applications (flow cytometry being my favorite). When describing the light output of a laser, the wavelength is given as some integer number of nanometers (eg. the main line of our HeNe laser is 488nm). Why? The nanometer wasn’t defined in terms of possible wavelengths, so I assume this an approximation. Do an infinite number of possible (non-integer) wavelengths exist?
That should have read, “the main line of our argon ion laser is 488nm.” The HeNe puts out 633nm IIRC
The wavelength of light can be any positive real number. There’s no quantization of wavelengths, and there’s nothing special about the nanometer.
I suspect the wavelengths are given as integers because the numbers aren’t accurate to more than 3 significant digits.
The wavelength of your lasers are just rounded off to the nearest nm for convenience. The people in my field also round to the nearest nm (1300 to 1550). I don’t know what the experimental accuracy to determine operating wavelength is.
The operating wavelength of your laser depends on a great many factors (type of material, density , temperature, length between mirrors, …) and while theoretically there are only a finite number of operating wavelengths or your basic material due to quantum mechanics, practically there is a continuous distribution of possible wavelengths around an optimal operating wavelength (although this distribution may be pretty sharp for lasers operating at very low temperatures and densities).
I’m guessing the theoretical optimal lasing wavelength for HeNe is around 488nm. The laser is then designed to operate at about this wavelength.
It’s just rounding. A HeNe laser’s red line (there are other HeNe colors – orange and green and two flavors of infrared) is 6328 Angstroms = 632.8 nm, or about 633 nm. That 632.8 could be taken to more decomal places, too, but you start runniong into the fact that the line isn’t infinitely narrow, and it’s actually lasing across a range of wasvelengths, defined by the width of the missioon line and the resonant frequency and the “finesse” of the laser cavity. But with appropriate filters (or if you define the laser wavelength as the PEAK value) you can subdivide the lasing wavelength finer than tens of nanometers. If you want to see emission spectra given to such a high degree of accuracy, look up the Persistent Wavelenmgths in the CRC Handbook of Chemistry and Physics, or get a copy of the MIT WAvelengths Tables.
They’re not. My graduate school research involved UV irradiation. I recall seeing citations in the literature to non-integer wavelengths (e.g., peak wavelength of UV light for purposes of killing bacteria/viruses is 253.7 nm, IIRC). But that was often rounded up to 254 nm.
My impression is that when you’re talking about a billionth of a meter, round-off does not cause a significant error.