RF excited CO2 lasers

[heruursciences]

Hello fellow RF CO2 wielders,
I've picked up one of these now, they are nice and small for the power. However it won't output. I have the single board driver 'sliced' pcb and it seems to be working fine. I measure 60V P-P sine at 27.12MHz at the end of the coax, laser end. Those of you with oscilloscopes, is that what you see? However at the FET gate on the laser the signal is only about 10V max and is no longer a sine. The input resistance of the 'RF in' of the laser measures about 48 Ohms, does that match your readings?

What sort of drive board do you have 60V P-p from the sliced board sound a bit high, if it is so, it may be an indication the laser driver transistor may be mounted wrong, or it may have a bad ground, or it may have an impedance mismached drive cable.

 

[drlava]

Hi, thanks Chris. Yep it's a slice of the 7 board dot matrix dd3. The cable is RG59/RG58. At first it was 2 feet only, but a longer cable seemed to have better matching. Because of the very high voltage on the output of the pcb, I'm thinking the 30V gate limit on the final FET may have been exceeded when the 2 foot coax was used.

However the resistance from the gate to the other two leads on the FET is still > 20M.



Some relevant images:

Final drive transistor in question:

Waveform from slice PCB:

Waveform out of coax:

Waveform on gate of final power transistor on the laser:

 

[Hemlock_Mike]

Measuring gate resistance on a FET is usually futile. The gate is mostly a capacative path measured in picoF. An Ohm meter will sometimes show the capacitive gate charge up. I usually have to put them in a simple DC circuit and bias them a little. That is unless there is a massive failure causing a short.

HMike

 

[drlava]

Generally when I have had an FET fal it is due to the gate oxide layer being perforated, leading to a measureable resistance from the gate to the source. If the oxide is good, the resistance measurement is supposed to be futile

 

[Hemlock_Mike]

FET's and The BORG have something in common ---

Resistance is Futile...................

HMike

 

[lasernerd]

Now that I have my tube inside the pipe, I have designed the housing for the driver, PWM and extra heat sink. This housing will be a piece of aluminum about 13" long and formed into a U shape.
The 18650 cells will attach to the exterior of the pipe.

NightStick -- I hope you get your transistor tomorrow.

Mike

glad your pro-creating with your laser's dude. Last time i stuck my penis inside the laser tube, i was shocked with 90v of IR electricity. How did you overcome the initial surge of volts from the diode blast?? When the blast initially came i reached my climax within the minute. Unfortunatly after this incident, the laser has made me impotent and i am unable to have sex with lasers anymore. Please tell me, how did u do it?

 

[Hemlock_Mike]

LNerd --

I had to read this several times to figure what you are saying :wtf:

This was an old post but I got it now -- :thinking: I never looked at it that way when I was building the CO2 housing..........
You're sick But funny !

HMike

 

[turtlecannon]

Hey guys, sorry to bump up an old thread but I finally took my laser off the shelf and tried to get it working a couple days ago and I need a bit of help. My laser is one of the later ones sold and is set up so that the laser head needs 32v and the board requires +12v, +5v, and PWM. I have been powering the head with five 6v 7Ah sealed lead acid batteries wired in series to produce 32 volts win fully charged. The driver board and PWM (one of the ones designed by Tottish) are being driven by a computer psu. My procedure goes something like this: First, I plug the batteries into the laser head. The red LED on the head turns on. Next, I turn on the psu. As soon as I provide power to the PWM, the RF OK and MOD OK LEDs on the driver board turn on. However, the laser is not lasing. Can anyone provide some insight as to what I'm doing wrong? Thanks!

 

[Hemlock_Mike]

TC -- Check your PM's. Sorry that it took me a while.

HMike

 

[LaZeRz]

If you need that your not much of a man.

Spam reported, lady.

 

[532 with Envy]

What garbage, let these looser peddle their drugs somewhere else! REPORTED.

On a side note this is a good old thread that is worth a read, I have one of these aircooled CO2's and Someday i'll put together a nice laser gun

 

[LaZeRz]

What garbage, let these looser peddle their drugs somewhere else! REPORTED.

On a side note this is a good old thread that is worth a read, I have one of these aircooled CO2's and Someday i'll put together a nice laser gun

Pics!! :wave:

I've seen watercooled 40w co2 tubes for under 150 dollars, might pick one up :eg: Thats what I call a burning laser.

EDIT: I gave you some rep for all the help you gave me regarding HeNe's

 

[alexbg]

I know this is an old thread....but I would like to bay one of this tubes ...working or not working

 

[Hemlock_Mike]

Sorry to find this late --- I have an old non-working tube.
PM me.
HMike