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Hello! I am in the odd position of being a (very) former engineer with absolutely no education in electronics. I'm trying to find a good starting point to learn, including underlying theory. I also think lasers are just plain cool. I would like to start working with them slowly and safely, and integrate lasers into the broader learning about electronics.
 





Welcome!

LPF has lots of knowledge available if you search long and hard enough. Some good posts are pinned to the top of the different categories too. I've got lots of parts available in my ebay store and on my website to get you started.
 
hwang21 said:
What kind of laser theory are you looking to learn about?
Click to expand...
That's good question! I'm at the "don't know what I don't know" stage.

  • I'm going to need some foundational electricity/electronics knowledge before I can build anything.
  • I've been looking for a good, basic educational resource that covers theory and practical elements. Like a class with a lab.
  • Finding an electronics lab/kit that doesn't deal with controllers and code would be a bonus.

For lasers, some of the basics that don't end in "then you use this calculator".

It might be a pipe dream, but I'd like to ease in along a 'curve' that makes refreshing my very rusty advanced math interesting and applicable.

As the kids say, TL;DR - I'm looking for a good place to start and not afraid of some math.
 
Admittedly, I'm not the best circuits person relatively speaking, so I'll just leave you with laser diodes are current hungry, and will overheat themselves without a constant current driver. A lot of basic circuit analysis assumes a constant voltage source, so be careful

Without really knowing how much physics background you have, I'd start with understanding the process of stimulated emission. That is the key characteristic that separates a LED from a laser diode, as both diodes, from a physical construction perspective, are quite similar

Unfortunately, the complexity of understanding laser physics and optics ranges drastically, from "ray optics" that describes reflection and refraction, for example: reflection is incoming angle = outgoing angle (with respect to a line that is normal/perpendicular to the surface), to "Fourier optics", which describes the manipulation of light by Fourier space transforms (assuming a far field approximation), for example: the object plane of a simple convex lens is the input, the lens acts as a Fourier transform, and the result from that transform is the image plane

Laser physics similarly ranges from "a line of light that can be represented as a beam of particles" to "quantum mechanical interactions of an electric field with a sea of electric dipoles", and the actual generation of laser light, the associated gain of a resonant cavity (Q factor), and the longitudinal modes of a particular cavity (no, most lasers are not actually a single wavelength) quickly falls into the quantum mechanical realm of physics

So, depending on your background and how deep you want to go, there is a lot, or a lot a lot, to dig into 🙂
 
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hwang21 said:
Admittedly, I'm not the best circuits person relatively speaking, so I'll just leave you with laser diodes are current hungry, and will overheat themselves without a constant current driver. A lot of basic circuit analysis assumes a constant voltage source, so be careful

Without really knowing how much physics background you have, I'd start with understanding the process of stimulated emission. That is the key characteristic that separates a LED from a laser diode, as both diodes, from a physical construction perspective, are quite similar

Unfortunately, the complexity of understanding laser physics and optics ranges drastically, from "ray optics" that describes reflection and refraction, for example: reflection is incoming angle = outgoing angle (with respect to a line that is normal/perpendicular to the surface), to "Fourier optics", which describes the manipulation of light by Fourier space transforms (assuming a far field approximation), for example: the object plane of a simple convex lens is the input, the lens acts as a Fourier transform, and the result from that transform is the image plane

Laser physics similarly ranges from "a line of light that can be represented as a beam of particles" to "quantum mechanical interactions of an electric field with a sea of electric dipoles", and the actual generation of laser light, the associated gain of a resonant cavity (Q factor), and the longitudinal modes of a particular cavity (no, most lasers are not actually a single wavelength) quickly falls into the quantum mechanical realm of physics

So, depending on your background and how deep you want to go, there is a lot, or a lot a lot, to dig into 🙂
Click to expand...
I have a BSE in Chemical Engineering that I earned in 1998. Ironically, I placed out of the physics requirement, so my only true physics class was trig based and in high school ~1989-90. Math up through Diff Eq. that I haven't used (beyond algebra) since 1998. A Physical Chemistry class (quantum chemistry) ~1997 with a one of those crazy professors that just makes you want to learn.

Qualitatively, I understand angle of incidence/angle of reflection, stimulating electrons to a higher orbital so they emit light energy when they return to their ground state, the concept of photons, etc.

I can't recall anything to do with Fourier and while I had 'quantum chemistry', I don't think it went as deep as you are describing. Think a 400 level course full of chem majors and a few ChemE majors to make them sweat about the curve.

Looks like I need to read up on:
  • Electricity basics
  • Electrical components
  • Optics
  • Efficiency of electronic devices (i.e. how much power into your overheating diodes is output and how much is heat)
  • LED vs laser diode - I have been wondering how you stimulate something in solid state like a diode!
at least for a start.

Thanks for talking this through with me to help focus the initial search. Do you have any suggestions for 'starter' materials?
 
Honestly, I find Wikipedia pretty solid for most of these topics, if a bit wordy at times, at least from the theoretical perspective

I think as far as optics goes, reading a bit about Ray optics should get you off the ground pretty well. From ray optics, the next step would be wave optics, which tries to describe the behavior of light from a wave/diffractive perspective rather than a particle perspective. One way to think about this difference is, with ray optics, a convex lens will cause a beam of light to meet at an infinitesimal point at the focal point of the lens. Clearly, that's not possible because that would mean a finite amount of energy has been concentrated to an infinitely small point of space, so an infinite energy density at the focus. Wave optics addresses situations like these that ray optics fails to address, but even ray optics gets you most of the fundamentals of the behavior of light in everyday scenarios. You probably won't need to touch Fourier optics at all 🙂

I'll give you a hint on LED vs. laser diodes - both are fundamentally made of what's called a semiconductor p-n junction

To way oversimplify, this is a sandwich type structure where the p side deliberately has a relative lack of electrons, and the n side has a relative excess of electrons, so the electrons and "holes" want to recombine. This recombination process emits a photon that corresponds to the particular bandgap (energy difference), just like an election dropping from a higher orbital to a lower one will emit a photon with an energy corresponding to the energy difference between those two orbitals

Both LEDs and laser diodes utilize this device structure, but with a laser diode, that recombination area where light is emitted has mirrors on each end of it that are something like 99% reflective, so that most (but not all) of the emitted light gets reflected back into the recombination area (creating a "resonant cavity", or a region of space where the light gets "trapped" and bounces back and forth a bunch)

Now, your homework is to understand how stimulated emission works 🙂 once you achieve what's called a "population inversion" in the recombination area, the photons reflected back will exponentially increase in number (called "gain" or Q factor). This number increases so dramatically that the 1% of light that escapes the mirrors? That is your laser beam 😎
 
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hwang21 said:
Honestly, I find Wikipedia pretty solid for most of these topics, if a bit wordy at times, at least from the theoretical perspective

I think as far as optics goes, reading a bit about Ray optics should get you off the ground pretty well. From ray optics, the next step would be wave optics, which tries to describe the behavior of light from a wave/diffractive perspective rather than a particle perspective. One way to think about this difference is, with ray optics, a convex lens will cause a beam of light to meet at an infinitesimal point at the focal point of the lens. Clearly, that's not possible because that would mean a finite amount of energy has been concentrated to an infinitely small point of space, so an infinite energy density at the focus. Wave optics addresses situations like these that ray optics fails to address, but even ray optics gets you most of the fundamentals of the behavior of light in everyday scenarios. You probably won't need to touch Fourier optics at all 🙂

I'll give you a hint on LED vs. laser diodes - both are fundamentally made of what's called a semiconductor p-n junction

To way oversimplify, this is a sandwich type structure where the p side deliberately has a relative lack of electrons, and the n side has a relative excess of electrons, so the electrons and "holes" want to recombine. This recombination process emits a photon that corresponds to the particular bandgap (energy difference), just like an election dropping from a higher orbital to a lower one will emit a photon with an energy corresponding to the energy difference between those two orbitals

Both LEDs and laser diodes utilize this device structure, but with a laser diode, that recombination area where light is emitted has mirrors on each end of it that are something like 99% reflective, so that most (but not all) of the emitted light gets reflected back into the recombination area (creating a "resonant cavity", or a region of space where the light gets "trapped" and bounces back and forth a bunch)

Now, your homework is to understand how stimulated emission works 🙂 once you achieve what's called a "population inversion" in the recombination area, the photons reflected back will exponentially increase in number (called "gain" or Q factor). This number increases so dramatically that the 1% of light that escapes the mirrors? That is your laser beam
Click to expand...
Oops. Getting the hang of the forum mechanics.

I did some reading on laser types (gas, organic dye, semiconductor and solid state). I think I understand the concepts, but I don't really have a sense of scope. Kind of like seeing prices but not knowing the currency.

I'll keep looking for something more basic, or an outline of which concepts to learn and the proper order.
 
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hwang21 said:
Honestly, I find Wikipedia pretty solid for most of these topics, if a bit wordy at times, at least from the theoretical perspective

I think as far as optics goes, reading a bit about Ray optics should get you off the ground pretty well. From ray optics, the next step would be wave optics, which tries to describe the behavior of light from a wave/diffractive perspective rather than a particle perspective. One way to think about this difference is, with ray optics, a convex lens will cause a beam of light to meet at an infinitesimal point at the focal point of the lens. Clearly, that's not possible because that would mean a finite amount of energy has been concentrated to an infinitely small point of space, so an infinite energy density at the focus. Wave optics addresses situations like these that ray optics fails to address, but even ray optics gets you most of the fundamentals of the behavior of light in everyday scenarios. You probably won't need to touch Fourier optics at all 🙂

I'll give you a hint on LED vs. laser diodes - both are fundamentally made of what's called a semiconductor p-n junction

To way oversimplify, this is a sandwich type structure where the p side deliberately has a relative lack of electrons, and the n side has a relative excess of electrons, so the electrons and "holes" want to recombine. This recombination process emits a photon that corresponds to the particular bandgap (energy difference), just like an election dropping from a higher orbital to a lower one will emit a photon with an energy corresponding to the energy difference between those two orbitals

Both LEDs and laser diodes utilize this device structure, but with a laser diode, that recombination area where light is emitted has mirrors on each end of it that are something like 99% reflective, so that most (but not all) of the emitted light gets reflected back into the recombination area (creating a "resonant cavity", or a region of space where the light gets "trapped" and bounces back and forth a bunch)

Now, your homework is to understand how stimulated emission works 🙂 once you achieve what's called a "population inversion" in the recombination area, the photons reflected back will exponentially increase in number (called "gain" or Q factor). This number increases so dramatically that the 1% of light that escapes the mirrors? That is your laser beam 😎
Click to expand...
OK, so I have a deeper understanding of the p- and n-type semiconductors and the active layer. I understand stimulated emission: basically a photon of the 'right' energy stripping an identical photon from an excited electron in the active layer. From there, confusion so far. It seems that once emission is stimulated the electron stays in the active layer (not dropping to the n-layer) and is only excited again by absorbing a photon. This seems cyclical, with the stimulated photon ultimately going back into exciting the electron again. Clearly I am missing something. Could you put a name to this next topic?
 
When an excited atom encounters another photon of the same energy, it releases another photon, both in the same direction and phase.

These photons bounce between mirrors in the laser cavity, amplifying the beam.

There is a rear mirror and the front mirror/facet has a small output region.

images


 
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What you're encountering is called the "population inversion". Stimulated emission only works if the incoming photon interacts with an electron that is already in an excited state, and it needs to be in a particular excited state such that the incoming photon's energy matches the excited electron's energy difference by jumping to a lower orbital. Only in this situation does the excited electron relax, emitting its own photon that happens to have the same energy, direction, and phase as the incoming photon. The incoming photon emerges from this interaction untouched, and so now we have two identical photons, and this process can repeat with another excited electron/atom

The end result is that in order for stimulated emission to continue, there must be more excited electrons/atoms than unexcited electrons/atoms in the resonant cavity. If the majority of atoms are not excited, then you are correct, the incoming photon would be absorbed, bumping an electron to a higher orbital, and when that electron relaxes, it emits the photon again (1 photon in, 1 photon out). Only in the situation where most/all of the atoms are already in said excited state, does 1 incoming photon + 1 excited electron/atom become 2 outgoing photons and one unexcited electron/atom

Oh, and you can excite an electron by means other than absorbing a photon. Energy (or really in this case, angular momentum of the electron) is energy, so as long as you input the right amount of energy, an electron will be excited to a higher state, regardless of where that energy actually came from. So, you can use a photon, you can use heat (think of a glowing red hot piece of metal - you have put in so much energy into the metal in the form of heat that electrons are being excited to higher orbitals and when they relax, they emit visible light - red light), you can use electric field, etc. In fact, an electrical conductor is only different from an electrical insulator by how difficult, or how much energy, needs to be supplied in order to get those electrons excited to such a high orbital (so far from the nucleus) that they end up leaving the atom entirely. Once they have left, the electrons are now a freely moving charge of electricity, i.e., electrical current. So, a conductor is a material such that a relatively low amount of electrical potential (voltage) can excite electrons to leave their atoms and flow freely, while an insulator is a material such that a relatively large amount of voltage is required to excite its electrons to leave their atoms. What does that make a semiconductor?
 
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