Is harmonic resonance in Photoreceptors explored?

Question

Look at the resonance curves of the L-cone (OPN1LW) in humans, it has its peak at ~570nm and rises up in the lower wavelength (higher frequency) area. For me as a musician, that looks like a natural harmonic 2/3 response – the fifths – of the frequency. But all spectral response charts I've found so far for the different receptors in humans don't really go beyond the borders of the range visible to humans.

Has someone a link to a study that tested for harmonic responses or general response in a field extending at least one octave in both directions, hence about 200nm - 1600nm, for the actual receptors (rods/cones) without surrounding effects like the lense being a low-pass-filter etc.

Answer 1

Vision works by a pigment molecules changing conformation by absorbing a photon. A certain range of energies is necessary for this conformation change.

More generally, molecules can potentially absorb multiple photons simultaneously rather than individual photons, and the combined energy of multiple lower-energy photons can excite the molecule to the same state as a single higher-energy photon. This is commonly utilized in biological experiments via 2-photon microscopy. Because 2-photon excitation requires simultaneous arrival of two photons, you need much higher intensities of light.

Here's an example of a paper discussing this in rhodopsin:

Palczewska, G., Vinberg, F., Stremplewski, P., Bircher, M. P., Salom, D., Komar, K., ... & Palczewski, K. (2014). Human infrared vision is triggered by two-photon chromophore isomerization. Proceedings of the National Academy of Sciences, 111(50), E5445-E5454.

Answer 2

I think a few things are muddled here. The frequency response profile of a cone (which is an entire cell) is a functional response to excitation of that cell's photoreceptors. It's easy to show that these cells only function over the range of wavelengths that are considered "visible range." So that's why you won't readily locate experiments that address your query. (I think a link to the data you're asking about would help.)

Since the underlying light-detection event here is the photo-isomerization of rhodopsin, there's no reason to think the process (at that scale) would occur at harmonics you're familiar with from music theory. That's because electronic transitions correspond to well-defined frequencies (as with the photoelectric effect). The rhodopsin molecule, like most pigments, isn't well-approximated as a harmonic oscillator (unlike, say, a guitar string) which is the whole reason classical electromagnetic theories failed to predict the emission spectrum of hydrogen.

So you're mixing-up your natural phenomena; biological photoreceptors behave somewhat-like the hydrogen atom, not like a guitar string. As you can see, the emission or absorbtion spectra of hydrogen do not have simple overtones of a fundamental frequency.