Holmium laser produce liquid jet one meter high !

[planters]

Thank you for the comment. Let me say that I envy your present situation where you are working with several different lasers and investigating various questions. I made a joke about your Holmium jet because of this freedom.

Those images are about one year old and I have been working on this laser exclusively during this time. I did not make a video of that original version because I never reached what I considered a definitive point of completion. I have made so many changes it is hard to remember them without my log book.

1. The laser in the image was externally triggered, produced up to 10 J in a 50usec pulse, was limited by the xenon lamps' voltage hold off to 2800V and approximately 1000J input. At maximum power the divergence was 30mrad.
2. A thyratron and then a spark gap replaced the external trigger and allowed additional power to be sent to the lamps. This increased the pulse duration to 60 usec due to the additional inductance and the power then plateaued at 20J and the divergence increased further to 40mrad. Additional input energy only increased the pulse duration.

3. Several different lamps were tried. First two then 6 and then again two, but these last two lamps were much larger, ablating wall lamps and the triggering was changed to a high voltage pulse injected parallel to the main, directly coupled, discharge circuit. The adjustable pressure in the ablating wall lamps allows the voltage stand-off to be set to match the discharge voltage and so the spark gap was removed. This last lamp configuration (the current set up) produces 12usec discharges and the laser pulse is up to 8usec long. I estimate the energy at 70J , but the calorimeter I was using to make this measurement was damaged..

The divergence is still high at 40mrad and the power output again plateaus even though I can easily increase the input beyond the 3000J where the power ceases to increase. I believe the gain is becoming so high that the highly divergent rays are simply not exiting the cavity, but develop suffecent gain to lase into the pump chamber. By lowering the dye concentration in order to lower the gain I can demonstrate that the lamps can continue to produce more light and more laser energy beyond 3000J input.

I have tried several unstable cavities that are reported to significantly reduce divergence. The simplest was a positive branch confocal resonator with a magnification of two and out coupling via an annular scraper mirror immediately in front of the convex, high reflector. I am also going to try to modify the pump chamber to a non-imaging parabolic concentrator to allow me to reduce the cell diameter from it's current 21mm to a significantly lower cross section. This looks promising as it will allow higher dye concentrations as well.

[femtoman]

Organic laser dye are know to yield a large gain.
The remarkable difference between a laser dye amplifier and a solid state amplifier is the lifetime of the upper laser level. In the dye the level is in the nanosecond and in the solide state in the millisecond.
Therefore it is not possible to store energy in a dye for more than a few nanoseconds. Consequently, the single pass gain in solid state depends more or less on the light energy supplied by the flashlamp, while in an organic dye the gain will be proportional to the instantaneous light intensity.
In solid state the saturation intensity Is is rather small (few kW/cm2 ). The stored energy ES can be quite high ( a few J/cm3 ).
In a dye laser, however, Is is about two order of magnetude higher but the storage capability is very poor. Up to now it does not seem possible to reach such a high intensity by flash pumping. Experimental value lie in W=2.10^6 sec-1 .
Different concentration N do not alter the shape of the gain envelope at constant pump power W.
This behaviour is at first sight surprising as one is used to dye lasers than can be tuned by concentration variation.
Net gain means the gain G increase exponentially with pump power, wich has been proved experimentally.
Optimising the gain? at very high single pass gains the amplifier will be saturated by its own amplified spontaneous emission (super-radiance).
This result means that the maximum single pass gain Gs obtainable is independant of any molecular parameter but only dependant on the geometrical dimension of the amplifier cell.
Gain G is rising roughly quatratically with lenght. However, radius and length of the amplifying cell can not considered independently.
To reach a high gain a very long thin cell is required.
Gs is only rising linearly with length. For a typical dye cell of L=10cm, concentration of the dye and pump power may be adjuted to reach a single pass gain ( in the visible) of Gs =3.10^6. Further increase of the pump power, eg, will not increase the gain but the dye cell will work in the super-radiant laser mode.
For a numerical example of saturation intensity Is = 100kW/cm2 for Rhodamine 6G.
For the dye laser pulses longer than a few nanoseconds will not be amplified to power levels exceding Is
Optimising the dye concentration? The gain coefficient g rises linearly with concentration. The highest useful concentration, however, is limited by self quenching of the fluorescence intensity.
Conclusion the best way is to have many shorts cells with large diameter and spacial filters between each cells to block the amplified spontaneous emission and a very short flashlamp pumping 10 nanoseconds.

[planters]

I believe the non-imaging concentrate-or will allow as much as 100kW of absorbed light within the pump bands of the dye. I am hoping to optimize the laser as an amplifier and to use it in an MOPA configuration. Mode locked, picosecond pulses from an oscillator, in pulse trains of a few thousand pulses, lasting several microseconds, will be injected into the amplifier. I am hoping to extract the energy stored in the upper state even though it is only available fro several nanoseconds.

[femtoman]

I believe the non-imaging concentrate-or will allow as much as 100kW of absorbed light within the pump bands of the dye. I am hoping to optimize the laser as an amplifier and to use it in an MOPA configuration. Mode locked, picosecond pulses from an oscillator, in pulse trains of a few thousand pulses, lasting several microseconds, will be injected into the amplifier. I am hoping to extract the energy stored in the upper state even though it is only available fro several nanoseconds.

Have you some photos from the laser ( 4 flashlamps) in action ? If not can you make some one ? Do you sell this cavity or make a deal with another laser from my collection?

[planters]

I do not have any more photos of that version of the laser. Have you ever seen "The Time Machine"? This laser is like the manikin in the window. Over the last year it has grown in length and narrowed in width, lamps have come and gone, the dye cell has changed in size and shape, feed lines have shifted and changed in number. I have had simple plano-plano resonators as in the photo and optics have multiplied up to even, at one point, an unstable, self imaging, self filtering ring resonator. It has served as an experimental test bed for published theory as well as some of my own bright ideas. Some of these are probably patent-able and others were pretty stupid.

I wouldn't want to sell this system, but I'm happy to work with anyone that wants to build these types of lasers.

[femtoman]

I wouldn't want to sell this system, but I'm happy to work with anyone that wants to build these types of lasers.[/QUOTE]

Have you make the mecanical parts of this lasers or a workshop ?
It is possible to make the same cavity and what is the price in a mecanical workshop?

I have started today the mecanical part for pumping a Nd:glass q-switch laser with 2 helicals 8kJ flashtubes.

[planters]

I have started today the mecanical part for pumping a Nd:glass q-switch laser with 2 helicals 8kJ flashtubes.

This will be very interesting to follow.