TL;DR

Reducing loss of energy

Hi
I was told by someone that if you place the laser in a vacuum, then if would not loose energy. Is this true?

Not only laser but light in general do not lose energy in vacuum.
Laser beam go in one direction. A beam receiver get the energy without the loss. Light, for an example sun light, goes all the direction whose energy density drops by r^-2 law. Total r^2-surface surrounding the light source get generated energy without loss.

@Josiah -- Please take care not to try to reopen a closed thread. Your previous thread on this question was closed because you veered off into non-physical territory with your laser power questions. I will let this thread here proceed, but only if you stick to known Physics.

Here is how your previous thread was tied off:

PeterDonis said:

The OP question has been sufficiently addressed. Thread closed. Thanks to all who participated.

Josiah said:

This is not a valid reference. Can you find a valid reference (textbook or peer-reviewed paper would be best) that says what you're asking about? If not, we can't discuss it here.

DaveE said:

Another application is in vacuum spatial filters, where the beam is focused so small that the energy breaks down (ionizes) the air molecules.

I was at a photonics trade show many years ago, and as I walked down one of the aisles, I heard a "snap, snap" noise every few seconds. As I got closer, I saw that it was a large laser (about the size of a small car, including the power source), and they had it set up to focus the pulsing beam in the air behind some clear shields. You could see the ionization at the focus point with each laser pulse. Pretty impressive.

https://www.edmundoptics.com/knowle...es/lasers/gaussian-beam-propagation/?hl=en-US

I am no expert in laser technology, but I found the above article helpful!

A laser in a vacuum (I'm thinking here, laser light traveling in a vacuum) does not lose energy since there's nothing to lose energy to (with the exception of the cosmological red shift effect), but no laser is perfectly collimated. Diffraction effects at the edges will always spread the laser out and the spread for a perfect Gaussian beam (which no real laser achieves, but can be used as an estimate based on the above article) is given by eqn 3 in the article:

$$
\theta=\frac{\lambda}{\pi w_0}
$$

Where ##w_0## is the initial beam width (see fig. 1).

If you plug in some reasonable numbers for that you'll see how your beam spreads out. Once you see how your beam spreads out you can calculate how much energy a certain observer some distance away would receive from your laser.

I was thinking you're interested in finding out if you can send a light signal very far away. But say you shine a laser at Alpha Centauri, 4 light years away, you'll find that even if you had a gigantic laser (of order meters wide in lens shape) the laser would still get spread apart quite a bit by the time it goes 4ly.

Matterwave said:

...a perfect Gaussian beam (which no real laser achieves...

Yes, they do. Single frequency TEM₀₀ propagation is a thing people have been using for nearly 50 years. About as perfect as anything in modern technology. That's how the computer you're looking at was made. Also, for many lasers it's where most of the energy is in the far field even if they have higher order modes too.

DaveE said:

Yes, they do. Single frequency TEM₀₀ propagation is a thing people have been using for nearly 50 years. About as perfect as anything in modern technology. That's how the computer you're looking at was made. Also, for many lasers it's where most of the energy is in the far field even if they have higher order modes too.

Ah gotcha. I don't know this field that well, I was simply parroting back the article:

In many laser optics applications, the laser beam is assumed to be Gaussian with an irradiance profile that follows an ideal Gaussian distribution. All actual laser beams will have some deviation from ideal Gaussian behavior.

DaveE said:

That's how the computer you're looking at was made.

Can you elaborate? Do you mean photolithography used in IC fabrication?

berkeman said:

Can you elaborate? Do you mean photolithography used in IC fabrication?

Yes. Lasers are used at many steps, each tailored to their very specific task. There ate many applications; mask creation and inspection, wafer inspection before & after, photoresist exposure, annealing, dicing, via drilling... I'm definitely no expert, but I'd put my bet on mask creation as the most sensitive to beam quality.

DaveE said:

Yes. Lasers are used at many steps, each tailored to their very specific task. There ate many applications; mask creation and inspection,

No, high end masks are written by e-beam lithography, either by VSB (variable shaped beam) machines, or by electron multi-beam (grey scale pixel based) mask writers. Inspection can use lasers for OCD (optical scatterometry), but defect review and repair is done again by e-beam (or ion-beam).

DaveE said:

wafer inspection before & after,

wafer inspection is „horror“, because features are too small for optical inspection, and e-beam inspection is still too slow. So OCD is always used, but alone it is insufficient. During process development and pre-production, e-beam inspection is used in addition, but it has its own challenges, in addition to being slow.

DaveE said:

photoresist exposure, annealing, dicing, via drilling...

Well, laser drilling of silicon vias would be too slow and error prone. Reactive ion etching is your friend here. No idea whether PCB vias are drilled by laser.

DaveE said:

I'm definitely no expert, but I'd put my bet on mask creation as the most sensitive to beam quality.

I do work in „semiconductor manufacturing“, decide for yourself whether that makes me an expert.
Many of those decisions what to use for which task are based on engineering considerations, like speed vs robustness vs accuracy vs costs. With e-beam VSB mask writers, mask inspection and repair is a fixed part of the process. And sometimes the mask has to be written a second time, because even repair could not fix it (in less than a day). Such a process is totally OK for mask writing, but a complete no-go for writing some layer of a chip.

gentzen said:

No, high end masks are written by e-beam lithography

I guess I'm not surprised I'm out of date here. I've been out of the tech game for a while now. We sold Ion lasers to Etec Systems* for many years for mask creation. Also to KLAC for inspection.

* Now part of AMAT

DaveE said:

I guess I'm not surprised I'm out of date here. I've been out of the tech game for a while now. We sold Ion lasers to Etec Systems* for many years for mask creation. Also to KLAC for inspection.

I always associate the MEBES e-beam mask writers (and the corresponding file format) with Etec. But they also had the ALTA advanced scanned-laser mask lithography tool product line. Today‘s laser-based mask writers mostly come from Mycronic (https://www.mycronic.com/product-areas/photomask-equipment/Products/slx-series/#description). I think they use UV laser diodes, with a wavelength somewhere around 350 nm. Probably ALTA used similar wavelengths, to avoid the hassle with chemically amplified resists.