Can we produce a white laser from a visible light spectrum?

In summary, the professor wants you to use two prisms to produce a visible light spectrum and then use another prism to converge the spectrum back into a laser. The theory behind the method is that by principle of reversibility there should be a way to convert the spectrum back to a laser. However, the temporal dispersion is still there. The professor suggests using chirped pulse amplification to fix the issue.
  • #1
athrun200
277
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I am doing a final year project, my Prof gave me 2 prism.
He wants me to do so:
A white laser is shot on a prism producing a visible light spectrum, use another prism to converge the spectrum back into a laser.

For me, it is theoretically impossible and I tried to convince him that it doesn't work as prism can only make the light more disperse. But he insisted that by principle of reversibility, there should be a way to convert the spectrum back to a laser.

Is he really correct? I want to disprove his statement but I cannot figure out a concrete proof.

I don't know what to do now.
 
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  • #3
You can easily produce white light by combining different colors via a prism. You can't make a laser out of it, as a laser uses stimulated emission to produce a coherent beam of light that consists of a small range of wavelengths, but you definitely make plain white light.
 
  • #4
Drakkith said:
You can easily produce white light by combining different colors via a prism. You can't make a laser out of it, as a laser uses stimulated emission to produce a coherent beam of light that consists of a small range of wavelengths, but you definitely make plain white light.

That means even if the original light source is a laser, it will become a plain white light after 2 prisms?
 
  • #5
Do you have a white light laser? I think that they all use super-continuum white light generation techniques, like this one: http://www.nktphotonics.com/superk_compact

So let's assume you have a laser with significant bandwidth; the ultrafast lasers I work with have bandwidth of 20-50 nm. For a "white light" laser you would have about 350 nm of bandwidth: 400 nm (deep blue) to 750 nm (deep red). For any of these broad-bandwidth lasers you will also have temporally short pulses: typically less than one picosecond, down to 10 femtoseconds. This is the ultrafast pulsed laser temporal range.

Now send the pulse through a prism: the colors separate (disperse) due to the differing speeds of light through the glass. They will also exit the prisms with different angles, so your pulse will be spread spatially, and temporally: the colors are fanned out spatially, but the blues will have exited first, and the reds last-hence they are also fanned out temporally.

The usual way to use prisms is in pairs: you adjust both members of the pair so that the beams enters/exits at the "angle of minimum deviation". You can actually use your eyes to determine this physical alignment, and after the beam exits the second prism it will be "all travelling" in the same direction again: the dispersion is cancelled.

However, your temporal dispersion is still there.

The fix for this is to be found in the design of the ultrafast CPA laser: CPA=Chirped Pulse Amplification. My thesis advisor was one of the inventors of this method in the late 1980s; see http://www.cap.ca/fr/node/709

Here is a nice picture with explanations: http://en.wikipedia.org/wiki/Prism_compressor

But it is easier to work with gratings; then you don't get non-linear optical interactions within the prisms!
See http://en.wikipedia.org/wiki/Chirped_pulse_amplification
 
  • #6
UltrafastPED said:
Do you have a white light laser? I think that they all use super-continuum white light generation techniques, like this one: http://www.nktphotonics.com/superk_compact

So let's assume you have a laser with significant bandwidth; the ultrafast lasers I work with have bandwidth of 20-50 nm. For a "white light" laser you would have about 350 nm of bandwidth: 400 nm (deep blue) to 750 nm (deep red). For any of these broad-bandwidth lasers you will also have temporally short pulses: typically less than one picosecond, down to 10 femtoseconds. This is the ultrafast pulsed laser temporal range.

Now send the pulse through a prism: the colors separate (disperse) due to the differing speeds of light through the glass. They will also exit the prisms with different angles, so your pulse will be spread spatially, and temporally: the colors are fanned out spatially, but the blues will have exited first, and the reds last-hence they are also fanned out temporally.

The usual way to use prisms is in pairs: you adjust both members of the pair so that the beams enters/exits at the "angle of minimum deviation". You can actually use your eyes to determine this physical alignment, and after the beam exits the second prism it will be "all travelling" in the same direction again: the dispersion is cancelled.

However, your temporal dispersion is still there.

The fix for this is to be found in the design of the ultrafast CPA laser: CPA=Chirped Pulse Amplification. My thesis advisor was one of the inventors of this method in the late 1980s; see http://www.cap.ca/fr/node/709

Here is a nice picture with explanations: http://en.wikipedia.org/wiki/Prism_compressor

But it is easier to work with gratings; then you don't get non-linear optical interactions within the prisms!
See http://en.wikipedia.org/wiki/Chirped_pulse_amplification

Yes, I have a white light laser. Thanks so much, it's so informative.
In fact, my Prof restricts me to use 2 prisms only, no grating is allowed.

I will give it a try tomorrow in the lab!
 
Last edited:

1. Can visible light be converted into a white laser?

Yes, it is possible to convert visible light into a white laser through a process called sum-frequency generation. This involves mixing two or more different colored laser beams together to create a white light beam.

2. What is the difference between a white laser and a traditional laser?

A traditional laser produces a single, specific wavelength of light, while a white laser produces a broad spectrum of light that appears white to the human eye. Additionally, white lasers typically have lower coherence and higher intensity compared to traditional lasers.

3. What are the potential applications of a white laser?

A white laser can have a variety of applications, including use in displays, lighting, spectroscopy, and medical imaging. It can also potentially be used in data communication and optical data storage.

4. How is a white laser different from other sources of white light, such as LEDs or incandescent bulbs?

Unlike LEDs or incandescent bulbs, which produce white light by combining multiple colored lights, a white laser emits a single, coherent beam of light that covers a broad spectrum. This makes it more suitable for applications that require precise and intense white light.

5. Are there any limitations to producing a white laser from the visible light spectrum?

While it is possible to produce a white laser from visible light, there are currently limitations in terms of efficiency and cost. The technology is still in its early stages of development and more research is needed to improve its performance and make it more commercially viable.

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