[Andy_Ruan]

Hello there!
I was wondering which branch of chemistry would fall under light induced metallic precipitation:
i.e using laser light to precipitate a metal out of a solution. (I am an interested high schooler who
has nothing to do for the summer and wish to study more into this :'))   
I tried to search the internet, but my search results were really random and confusing

I came across resin based 3D printing, and wondered if it was possible to do the same, except with
laser light and some sort of solution containing dissolved metal ions.
https://www.youtube.com/watch?v=VTJq9Z5g4Jk

[Enthalpy]

Hi Andy-Ruan,

My main concern, as a gut feeling, would be that the metal precipitates in the liquid as a solution, rather than depositing a layer on the existing solid metal.

Maybe the light shouldn't precipitate the metal directly, but create an intermediate which decomposes only upon contact with the solid metal, like the classical silver on glass does.

Be prepared to use intense light. Mma polymerization joins many unit cells from one photon. Salt decomposition would supposedly need as much light as laser sintering.

[Enthalpy]

If you could deposit just one layer of metal at locations controlled by light, that would already be useful, even without stacking many layers to make 3D items.

You could make printed circuits more quickly.

You could make grating lens.

It wouldn't need a laser, by the way. Just light, more or less concentrated, depending on the goal. That's easier, because for instance UV Leds exist commonly while UV lasers are badly available.

[Andy_Ruan]

Oh that sounds really interesting 
Do you think it would be possible to to deposit metal at the same rate as metal sintering?
For circuitry, they use a photoresist only several microns thick, so not that intense of light
is needed.  I would imagine the enormous energies needed to create a structure in such a
solution o.o

Also!
I was also looking into solid metal forming in a solution, and I came across a video with
tin chloride -under intense current - that forms tin crystals! 
https://www.youtube.com/watch?v=r-YbQN_twpw
Would it be possible to recreate this with constructively interfering EM waves?
(there could be multiple sources that congregate at only one point so that it only
affects that one point and not the surrounding liquid, similar to MRI machines).  That way, a point of a specific
energy (which can ionize specific atoms) can be readily manipulated in 3D space!

Sorry if this idea seems a bit out there but I feel like there could be so many applications
to this!  Imagine being able to have several tanks with different metal ions and even resins
that can fully automate the manufacturing process.  Likely not for industrial manufacturing, but
perhaps for unique, more detailed and complex structures.

[Enthalpy]

Photoresist may be thinner than metal for a printed circuit, but above all, one photon affects several patterns of the polymer, which saves light. Metal deposition by light would just save the photoresist step but consume more light. Whether it's better depends on many aspects, like how fast, and so on.

You might try instead to produce locally an etchant by light, and start from a uniform copper instead of uniform insulating surface. At least, this doesn't need the clean deposition nor the adherence, which are both nontrivial. Maybe the chemists here can suggest molecules for it?
- Atomic oxygen from some sort of peroxide, hypobromide...?
- Singlet oxygen?
- Others?
Etching copper has immediate uses, but just blackening a clear metal must have some applications.

I suspect - but haven't seen reports about it - that your closest competitor is a pulsed laser that evaporates the thin copper (35µm and 17µm are common) where desired. This process is the cleanest, has the least steps, needs the least skills to use a machine. Automatic milling machines exist for that exact purpose but their result may be less clean.

Interferences: they are independent of what process uses the photons, and do make patterns on photoresists too. Whether you achieve that with a liquid (or a paste!) must depend on how much the fluid migrates while you irradiate it. This includes diffusion, that is, Brownian motion.

For instance, the patterns on integrated circuits (chips) use interferences, in the sense that simple edges in the mask would produce diffraction fringes in the photoresist, but to combat it, the masks has carefully computed fringes whose interferences minimize the fringes at the photoresist.

As an other example, many simple patterns in photoresists, including zone lenses and sometimes diffusion gratings, are made as interference figures. Interferences really tell how many photons, how much energy arrives where, with all the consequences, be it on a screen, a photoresist, a metal deposition if you achieve it. Interferences are by the way not just fancy figures on special occasions, they are the deep nature of light and generally waves, and tell how a lens works for instance.

Control at will an interference pattern... Yes with limits, and presently it's not done in home labs.
- If the control elements change accurately the phase and amplitude, then nearly any interference pattern is possible, and the math is accessible to engineers. Aperture synthesis works this way in sonars, radars and radiocomms.
- The technology isn't mature enough for light. I've never seen a board of 10,000 lasers whose individual phase is controlled by data cables. What exists is one light source and a many-pixels reflector where the individual reflection amplitude is controlled, but the phase not properly to my knowledge.
- With such limited hardware, one may try to produce interefence patterns, but of poor quality, and with much stray light. Consider this as lab research, very far from making a printed circuit.