Flashlamp Video

[planters]

As long as he will not be able to take your drawing and enter into a CAM program then I agree, just draw it up. This is just too simple. The only guiding measurements are the OD and the ID of the glass tube and the axial hole that you will tap for a hose barb. Expect this to be 16-27 NPT or a machine thread 10-32.

[Draco]

sorry i was making it more complicated then it is

[femtoman]

Femtoman,


I am enjoying this discussion, but I have to disagree with you on several points. The wall ablation regime does indeed begin much lower than 200J/cm^3. This is supported in the literature where evidence of wall material begins to appear in the output spectrum and by analysis of the gas drawn out of the tube when operating in a flow through mode.

More than this, it can be demonstrated. Run a typical tube at low energies (below 20J/cm^3) for several hundred pulses. Observe the walls of the lamp near each electrode, especially if high erosion electrodes machined out of aluminum are used. There will be several cm of grey/black deposit that builds as the pulse count mounts. This material cannot be cleaned chemically, but a single higher energy pulse above approximately 50J/cm^3 will completely remove this material. If the tube is now run at this higher energy, the deposits do not return. This is why I questioned the tube in your image. It should be clean unless the material is not glass and the UV flux is causing some dye or other organic to be deposited.

Energies above 200J/cm^3 will be hard to achieve in real life tubes larger than 6mm ID. Indeed, in your coaxial tube with a 7mm OD inner tube and a 8mm ID outer tube which gives an annular gap of 0.5mm, multiplied by the tube length which I would estimate at 35cm gives a volume of approximately 4cm^3. Even at 500J you would only be at 125J/cm^3. By my measure you were well within the ablating regime, by yours, you were not much above 1/2 way to the bottom of the range.

Several decades ago when Russian researchers set the world record for a single dye laser pulse at 400J, they also used a coaxial lamp, however because of the large dimensions of their dye cell it may be that their lamp was not operating in the optimal loading range. They were using approximately 50kJ in an approximately 10us pulse. Based on some discussion by Duarte, it may be that the holy grail of short duration pumping may be less important than absolute peak power no matter the duration.

Although I suspect that pulse length has some significance it is not usually factored into the ablating threshold determination. It will most likely be that the shorter the pulse, the lower the transition from line emission to thermal radiation of wall products. I say this because a more rapid pulse will diffuse less into the bulk of the glass, reserving the energy and increasing the surface temperature. Nevertheless, I am seeing ablation in my 16us pulses.

Planters,

A good article is " High-Energy Dye Laser Pumped by Wall-Ablation Lamps" Applied Physics15, 191-196 (1978) from TT.Okada
and "Ablative Flashlamps for High Power Peak Power Dye Lasers" APPLIED OPTICS Vol.16 No.8 p2293 - 2296 from Y. Levy G.Neumann

you can see the luminescent Spectrum of a flashlamp D=5.5mm and L=150mm at 10 torr air pressure with different input energy.

At 12J you can show the typical line Spectrum from the gas (air)
At 85 J you have the lines fom gas +lines from the wall ablating (effectively you have juste the wall ablating effect start at 25J/cm^3)
At 421 J you have a continuous spectrum like a black body.

In my laser i have 2uF 25kV 625J and 2.9cm^3 that is 215J/cm^3 i preview to work with 6uF

I have an article from Russian that give value from 200J/cm^3 to 2kJ/cm^3 effectively the wall ablating process start at 25J/cm^3 !

The big problem with wall ablating tube is that at high energy the hot plasma is absorbant for the light emission that muss traverse the plasma column
and the best way is to have a lot of flashlamp with on reflector . I think a good value is to be in the 100 to 150J/cm^3 input energy

[planters]

Arnold,
Those are good articles and I have them. Thank you for looking into this with such diligence. The high temperature plasma does absorb and re-emit the high energy photons as a black body. This process does not have a quantum defect and so the only manifestation is a prolongation of the emission process. The effect of the cooling (emitting) black body is that the light pulse duration depends on the wavelength you are measuring. In the article by Levy he notes that their pulse duration varied from 1.8 usec at 377nm to 3.4usec at 560nm. I measure my light pulse duration with a simple biased photo diode, however the EFFECTIVE wavelength may have a substantially shorter duration than my unfiltered measurement. This may also explain the "early termination" of flash lamp pumped, dye laser output. This property is blamed by many authors on photoacoustic disturbances from the pump pulse. Maybe it is simply that the usable pump light has simply ceased!

In my laser i have 2uF 25kV 625J and 2.9cm^3 that is 215J/cm^3 i preview to work with 6uF

This should be interesting. If you are already generating a substantial output, then increasing the pump energy 3x will probably generate more than an order of magnitude increase in output!

My laser produces large amounts of power and the problem is the optics. Well before I reach the limitations of the flashlamps, the cavity will need to be improved. I believe I now understand the principal behind unstable cavity optics. These are not intuitive, but they may act in the same way as a MOPA by selecting a small aperture within the gain medium and allowing the high quality, spontaneous emission generated here to be expanded to fill the medium for a single pass of amplification. You may need to go here as well.

[Draco]

i think i have scrounged up some parts to make a doubler for my project, i have 2 .2MFD 5kv caps and two diodes i had saved from a few microwaves , they should be over 2kv at about 600ma maby even an amp so i may need a current limit to the main caps, the main supply can and will do over 300ma at 2kv
That's my beast

[planters]

Something to keep in mind if you plan to run at a significant rep rate. A flow through system will tend to "pump" the gas with the discharge. The brief period of high pressure drives the gas from the tube. You might consider using a solonoid to close off the vacuum line during the pulse. This is what I do. Alternativly, you can do what I did on my early systems. Use two solonoid valves each one attached to the gas supply and the vacuum line respectively. Then "T" this to the cathode/ground end of the tube. By closing one and opening the other, you can fill and then flush the tube. This allows you to trigger the tube without a separate circuit and the gas pumping is not a problem. Probably limited to one Hz with this system.

[planters]

Oh, I forgot to mention that I like the PS in the kid's playroom. That worked for me as well.

[Draco]

Thank god i am the only kid allowed in my "playroom". I dont have kids near this place, when it comes time to visit my family i go to there home rather then here, more so with this new experiment and including my stuff with fireworks this is in my view the most hazardous device i have, i built the voltage doubler with what parts i have, it can clearly be improved but it does work, i charged one main cap to 2kv, i do need to install bleeder resistors, since i used a 1000:1 in the meter that does not provide enough resistance to self discharge in say less then 10 min, of course the fun way would be to just short it but i think that would damage the terminals lol
Harbor Freight (China Freight )has a sale on a cheesy drill press that i ordered so i will machine the brass my self, my other set up was lacking really bad, getting the part parallel is not going to work with what i have.
Thanks for the idea on using solenoids and since it does take a few seconds for my caps to charge i think that will work well

On a second thought the value of my caps in the doubler prevent an over current condition in my power supply

[planters]

The problem with the gas "pumping" is that subsequent pulses can spontaneously fire because the capacitors reach voltage before the tube pressure reach its pre-pulse steady state. Dealexteeeme has a nice two channel pulse generator that will allow you to set up an automatic system.

https://www.youtube.com/watch?v=qfvSTyVYUqs

[Draco]

Ok if i am interpreting this correctly I would use the timer to hold off the power supply that charges the main capacitors, or use it to hold off on the trigger pulse that would in turn fire the lamp.
I have two timers like the one posted , reading the manual for them is a nightmare due to the very horrible translation, the manual mine has calls the 8 segment led display (digital tubes),
trying other one i am trying to find documentation on it. The one i have running is an FRM01

on a plus both caps seem to be able to hold there rated voltage