6OOO mJ 6MW optical breakdown with TEA CO2 laser in action

[femtoman]

This progress bodes well for your breakdown pumped dye. Do you have the equipment to obtain a spectrum of the pulse? I have no doubt that it will have significant UV energy, but if you could determine where the peak occurs then even if there is VUV energy, the peak might allow you to estimate the temperature or at least set a lower temperature limit.

I have a fiber optic StellarNet photospectometer an i will make a measurement of the Spectrum from 200 to 900nm.



Whit the formation of a line focus on the quartz cell, i think that the temperature from the plasma is lower than a plasma ball.

Actually i have not obtained to pump the dye i will make some modification on my dye cell .

[planters]

That measurement will be interesting. I wouldn't be surprised if the peak occurs in the vacuum ultraviolet and your slope continues to rise at the short wavelength limit of your photospectrometer.


Have you tried adding COT to help lower the threshold?

[krazer]

Real interesting project, it is always nice to see hobbyists working on unique lasers like this. The the eximer laser require much in the way of modifications? I never really thought about it, but as long as the windows were made of something that transmits 10um it seems like it would be a 'simple' matter of hooking up a CO2 manifold and pressing run.

On a similar note - if your goal is to pump dye, is there a reason you chose to lase at 10um and upconvert to the UV as opposed to just lasing N2? I am not really familiar with high energy TEA lasers but the geometry of that laser looks like it would work fine running on N2, operating in a regime similar to the LN1000 TEA N2 laser. Even with the reduced efficiency you should get way more peak power and probably more UV as well, considering the not go great conversion efficiency to the UV in plasma generation.

[femtoman]

Real interesting project, it is always nice to see hobbyists working on unique lasers like this. The the eximer laser require much in the way of modifications? I never really thought about it, but as long as the windows were made of something that transmits 10um it seems like it would be a 'simple' matter of hooking up a CO2 manifold and pressing run.

On a similar note - if your goal is to pump dye, is there a reason you chose to lase at 10um and upconvert to the UV as opposed to just lasing N2? I am not really familiar with high energy TEA lasers but the geometry of that laser looks like it would work fine running on N2, operating in a regime similar to the LN1000 TEA N2 laser. Even with the reduced efficiency you should get way more peak power and probably more UV as well, considering the not go great conversion efficiency to the UV in plasma generation.

Hello Krazer,
Sorry my English is very bad it is possible you note understand my English ............. ?
I muss explain you that i have buy 2 scraped Excimer lasers EMG201 for only 250 euro each

One was in better state and i work with them with Nitrogen/helium at atmospheric pressure N2 TEA it give 16mJ
http://www.swissrocketman.fr/excimer...k,fr,3,272.cfm i will received end january the gas to operate in excimer XeCl with an output of 600mJ to pump my dye laser FL3002 http://www.swissrocketman.fr/dye-las...k,fr,3,273.cfm

The other one was incomplet and completly corroded and i decide to transforme this in CO2 TEA and make some amelioration to obtain an output of 10J the original output with Lambdaphysik is 6J.

The dye laser pumped with the linear plasma is only a idea to make new experiment!
Actually it is not working in my first test because my optical resonator is not aligned (very difficulte to aligne because the capillary has only 1mm in diameter. I will make another cavity with the Mirror directly glued on the capillary. (ready in 2 months i have a lot other things in parallele)

Clearly if i pump my dye with this laser working with excimer i can obtain 300mJ and with the CO2TEA converted in UV if i have 1 to 2mJ it was satifactory . The difference is the pumping dye with CO2 laser i have never show a publication about this !

[planters]

Peter,
Ya, it's the craziness that is so appealing, not the practicality.

Arnold,
You mention in a previous post that you were thinking about a femtosecond CO2 laser. Were you serious and if so what was the design?

[femtoman]

Arnold,
You mention in a previous post that you were thinking about a femtosecond CO2 laser. Were you serious and if so what was the design?[/QUOTE]

ANSWER
The important physical parameter to obtain femtosecond 10.6 micron CO2 pulse is the spectral bandwidth. In multiatmospheric TE CO2 laser at 10 bars the bandwidth is 1THz wide quasi-continuum that permit to amplifie 500 femtosecondes CO2 laser pulses.

The extractable energy at this short pulse is in order of 20mJ/cm3 that is 200J for a 10 liters amplifier.
The mode locking is made with a pockel cell.

It is note easy to make an homogen discharge under high pressure (need electron gun) another problem is the output window that support only 0.5J/cm2 during 500 femtoseconds

[femtoman]

Arnold,
You mention in a previous post that you were thinking about a femtosecond CO2 laser. Were you serious and if so what was the design?

ANSWER
The important physical parameter to obtain femtosecond 10.6 micron CO2 pulse is the spectral bandwidth. In multiatmospheric TE CO2 laser at 10 bars the bandwidth is 1THz wide quasi-continuum that permit to amplifie 500 femtosecondes CO2 laser pulses.

The extractable energy at this short pulse is in order of 20mJ/cm3 that is 200J for a 10 liters amplifier.
The mode locking is made with a pockel cell.

It is note easy to make an homogen discharge under high pressure (need electron gun) another problem is the output window that support only 0.5J/cm2 during 500 femtoseconds[/QUOTE]

[planters]

Arnold,
Just to review the numbers, 1 THz would be approximately 400um. What would be the bandwidth in um of the 10.6um radiation at 10 atmospheres?

0.4 Exawatt is indeed an incredibly high peak power and would certainly destroy optics when the beam is only a few cm. across. You might consider running at a lower peak pressure if the bandwidth would still support the short pulse. This would lower the stored energy as well as improving the discharge stability. Or, you could pre-ionize only a small fraction of the potential discharge length as well as enabling only that portion of the peaking transmission line. This would also reduce the stored energy.

[femtoman]

Arnold,
Just to review the numbers, 1 THz would be approximately 400um. What would be the bandwidth in um of the 10.6um radiation at 10 atmospheres?

0.4 Exawatt is indeed an incredibly high peak power and would certainly destroy optics when the beam is only a few cm. across. You might consider running at a lower peak pressure if the bandwidth would still support the short pulse. This would lower the stored energy as well as improving the discharge stability. Or, you could pre-ionize only a small fraction of the potential discharge length as well as enabling only that portion of the peaking transmission line. This would also reduce the stored energy.

Thelaser system consists of a picoseconds pulse-injector based on fast optical switching from the output of a conventional CO₂ laser oscillator, and a chain of high-pressure laser amplifiers. It starts with a wavelength converter wherein a near-IR picosecond solid-state laser with l»1 μm produces a mid-IR 10-μm pulse. This process employs two methods; semiconductor optical switching, and the Kerr effect. First, we combine the outputs from a multi-nanosecond CO₂ laser oscillator with a picosecond Nd:YAG laser on a germanium Brewster-plate to produce an ~200 ps, 10μm pulse by semiconductor optical switching. Co-propagating this pulse with a Nd:YAG’s 2nd harmonic in a Kerr cell filled with an optically active CS₂ fluid, we slice out a 5 ps, 10μm pulse at the ~0.1 MW peak power-level.

Immediately after a low-power, 10 μm, seed pulse is produced, it is amplified in a chain of high pressure (~10 atm.) CO₂ laser-amplifiers. At the first stage, the pulse is seeded into an isotope-filled CO₂ regenerative amplifier where it is trapped for 10-12 round trips and then released on reaching the ~1 GW level. A final high-pressure, large-aperture (10 cm) amplifier boosts the laser pulse to 1 TW. However, due to spectral modulation in the molecular-gas active medium, direct amplification of a femtosecond CO₂ pulse might be problematic, even when we consider expanding the bandwidth using enriched mixtures with isotopes ₁₈O and ₁₃C. According to our simulations, the gain bandwidth will limit the pulse’s duration at 1.5-2 ps. We note that shortening the pulse’s duration from the present 5 ps should nearly proportionally increase the energy extracted from the amplifier, or quadratically raise peak power. However, when an ultra-shot laser pulse acquires high intensity in propagating through the amplifier medium, undesirable nonlinear effects in optical elements and in the gas medium come to play that may cause uncontrollable stretching and distortions of the output laser-beam. We will lessen such nonlinear effects by incorporating a stretching/compression technique similar to that used in conventional femtosecond Ti-Sapphire laser systems. This approach, not yet realized for molecular gas lasers, can raise the amount of energy extracted from an amplifier by an order-of-magnitude. Therefore, stretching the 1-ps pulse to ~200 ps before amplification, and subsequently recompressing it to 1.5-2 ps will be very crucial in reaching our goal of approaching sub-PW peak power.

This is the final stage the 9 bars amplifier the dicharge voltage is 1MV !


The prospect for shortening the CO₂ laser’s pulse length to femtoseconds (few laser cycles) still exists. We will explore this possibility via new approaches to a picosecond pulse-chirping and compression inside or outside the laser amplifier. For the external compression, we will consider passing the laser beam through a pipe filled with xenon gas that has a high nonlinear refractive index, while keeping the laser’s intensity and the gas pressure below the ionization threshold. Then, Kerr effect-induced phase self-modulation in xenon dominates the spectral transformation of the laser pulse. Preliminary theoretical analysis shows that we can convert a quasi-linear frequency chirp, induced by xenon, into efficient pulse-compression in a dispersive element by nearly an order-of-magnitude without appreciable energy loss. A grating pair or a properly selected IR optical window may serve for such compression and should provide us with a few-cycle laser pulse.
Overall, via pulse compression and improved energy extraction from laser amplifiers, we anticipate an increase of over two orders- of- magnitude in the laser peak power up to 100 TW.

[planters]

Thanks for the discussion. Firstly, I thought you were affiliated with CERN. The overview is credited to Brokhaven.

In any case, this is the first I have heard of a semiconductor switch. That is very interesting. Is the switching speed for the 10um light only limited by the speed of the YAG or is there an added duration associated with the germanium as well?

The compression in the xenon is very good because it should allow large beam cross sections and would be scale-able as the power from the amplifiers increases. The current 5J is rather small compared to the impressive mass and power (1MV) of the final amplifier. Is there considerable allowance to increase the beam-plasma interaction length as it is folded through this stage?

You are considering using isotopes to broaden the gain bandwidth of the amplifiers. How significant is this isotope effect? Could you also broaden the bandwidth by modifying the buffer gasses or by introducing other molecular species such as CO?