Lasing mediums

[DoctorEvil]

Hello everybody, I've been hearing a lot about some new crystals with higher efficiencies than a standard yag, so who knows what the MOST efficient lasing medium is, it's pump wavelength and output wavelength etc. preferably ones that you have used or seen.

 

[BShanahan14rulz]

Only seen doubled yttrium garnet and vanadate, vanadate>garnet

 

[bloompyle]

Are you limiting this to DPSS? Might seem like a silly question.

However, every laser uses a gain medium. Some don't even need mirrors as they are "super radiant". Meaning the light produced in a single pass is enough to achieve proper lasing. Some are so super radiant, that using mirrors would actually burn out the mirrors used, or gain medium.

An example would be a copper vapor (CVL). Thes only use one mirror, and a totally transparent window to keep the vacuum seal. The one mirror is just to send the other 50% of the light out the output end.

Nitrogen lasers are also super radiant, and they follow the same criteria as above, even when pumped into a dye cell, they still remain super radiant. However there is sometimes an output coupler placed on one side of the dye cell to send that light back through to get 100% of the output on one side.

Laser diodes use a gain medium between two mirrored bits as well.

Research has found "random lasers" in plastics and other materials that have reflective surfaces that just happen to be parallel in the material. Scientists have studied this by shining green lasers on sheets of material, and getting red incident light from them reflected in the cavities.

Even more intriguing, "spasers" use a method of extracting photons, or "plasmons" embedded in layers of metal that are absorbed when certain wavelengths are shined on the metal. An analogy used involved an ocean of electrons. Visualize the sheet of metal as a sea of electrons. When a specific wavelength is directed to it, these photons can be trapped, and cause plasmons. Like the waves of the ocean being created by wind, these waves are created by trapped photons in the sea of electrons, or to be direct, trapped under the layers of metal. There is a lot of science being put into the study of "plasmonics" to find new and efficient ways to harvest these beyond the minuscule findings they have discovered. Currently, it requires a microscope to see said light, and a gain medium, or some sort of resonator to couple this output.

So again I ask, are you simply asking about DPSS?

 

[Sigurthr]

Even more intriguing, "spasers" use a method of extracting photons, or "plasmons" embedded in layers of metal that are absorbed when certain wavelengths are shined on the metal. An analogy used involved an ocean of electrons. Visualize the sheet of metal as a sea of electrons. When a specific wavelength is directed to it, these photons can be trapped, and cause plasmons. Like the waves of the ocean being created by wind, these waves are created by trapped photons in the sea of electrons, or to be direct, trapped under the layers of metal. There is a lot of science being put into the study of "plasmonics" to find new and efficient ways to harvest these beyond the minuscule findings they have discovered. Currently, it requires a microscope to see said light, and a gain medium, or some sort of resonator to couple this output.

I remember reading a research paper about surface plasmon physics a few months back, was very interesting stuff. Seemed like they were a long ways off from fully understanding or reproducing it on demand though.

 

[bloompyle]

Apparently, from what I read, they were only able to harvest a few photons (perhaps even only 1). It would be a very faint glow under a microscope.

Not sure how old the article was, just recently read about it

 

[Sigurthr]

Oh and about nitrogen, which is an excellent lasing medium, it has an Achilles heel; it takes a LONG time to get back to the ground state where it can be pumped again effectively. Pulse shaping and timing in N2 lasers is key.

 

[DoctorEvil]

No I was not restricting it to dpss. All mediums are welcome. How's that copper vapor laser work?

 

[bloompyle]

No I was not restricting it to dpss. All mediums are welcome. How's that copper vapor laser work?

There's a tube filled with copper. Either pure Cu, or a halide like CuBr, or CuCl.

Pure CVLs generally have some sort of refractory ceramic tube that can handle 1500C+, whereas the CuBr/CuCl uses a fused quartz, or borosilicate.

There is a heating element to heat either compound to it's vapor temp. For pure Cu, it's 1450C (give or take 50C), for the CuCl/CuBr, it's about 500-600C.

This tube also has low pressure He, Ne, or Ar (generally Ne). Also, there is sometimes a trace amount of H (about 2%) which produces a greater output.

For the rest of this, I will separate the CVL (pure) from the CuBr/CuCls, because now things get very different.

Pure CVLs require a single pulse of electricity down the discharge. This pulse results in transition of the Cu to it's excited state, then falling to metastable releasing photons (like your basic gas laser operates). The electronics here are fairly basic. However on each end you will find either a mirror, or a window. On one end, a mirror, the other a mostly transparent window. This is simply so all the output is funneled in one direction. Also, pending temperature of the Cu, you will have differing in the outputs of each line. There are two here, 510, and 578. In lower temps, the bell curve for 510 peaks higher than the 578, though as temperature increases, it starts to decline as the yellow increases. So pending temperature, you can have greater output in one over the other. Generally the goal is a 1:1, or 2:1.5, green to yellow ratio.

The lasers can be from hundreds of mW, to over a hundred watts in lab settings.

For the CuBr/CuCl, things are different.

You have two pulses of electricity, since the vapors are not pure Cu. You need to send one pulse to disassociate the copper from the halide resulting in pure Cu vapors. Then a second one to lase the Cu. These lasers are very complicated because these pulses need to be <100ns apart, <50ns for good efficiency, the lower the better.

After that, it's all the same.

These are used heavily in medical fields for treatments in the skin, there's a video on youtube of a Korean doctor using it on a patient's face. Not exactly sure what they were trying to accomplish however, my Korean is basic at best currently.

Anyway, that's your intro to CVL/CuBr/CuCl's

Enjoy the forums!