Ruby laser design process----make money online

hey everyone I've been collecting parts

over the last two to three years to

build a ruby laser and finally in the

last week or so I've got all the major

components here so that I can start

making an honest effort lasers are

basically light amplifiers and in this

case this is a helium neon laser and

we've got mirrors on either end and a

mix of helium neon gas in the middle so

the when we apply power to this the

helium neon gas emits light just like it

does in a plain old neon sign but the

trick is that the mirrors on either end

constrain this optical cavity to be

working in one direction since the

mirrors are facing each other the key is

that the laser medium

provides this light amplification with a

directional component so if we do the

mirror trick and align up these mirrors

very carefully we get a very thin

directional beam of light out of it

the same thing is true of Ruby so this

is a ruby rod that's synthetic and I got

this as I got this one off of ebay and

it's in pretty good condition there's a

NIC on one end here that's sort of

noticeable but otherwise it's okay and

this one is relatively large ruby is

just aluminum oxide that's been doped

with a little bit of chromium and for a

synthetic Ruby like this we can actually

control the chromium content to alter

its laser properties so unlike a

helium-neon laser where we can just put

electricity across it and have the

helium neon emit its own light just

through plasma excitation with a ruby

laser we have to provide the light from

somewhere else or we have to excite the

atoms in here some other way and

typically this is done with a large

xenon flash tube the idea is that when

the flash tube fires the chromium ions

in this Ruby rhod will become excited

just like the helium neon atoms become

excited in the laser over here just from

the light emitted by the plasma one

major difference though is the density

if the laser medium so in here it's just

a gas healing neon it's not even at

atmospheric pressure whereas here we're

talking about a solid so we actually

need quite a bit more light per volume

of laser medium

cuz it's just so much more dense and

this leads us to very large and powerful

flash tubes so I'm going to talk about

in this video so as you can see I've

been collecting quite a few large flash

tubes this one is quite intimidating the

problem is that it's so much larger than

the Ruby rhod there's no easy way to get

all the light from this flash tube into

the Ruby the idea is that we want this

flash tube to go off and then all of the

light will go into the Ruby rhod and

excite it so that it can start lazing

one way to achieve this is to use a

helical flash tube like this this is

from a professional photographer setup

but as you can see again the flash is

not quite enough to cover the whole -

what we really want is something that

will get light into the entire tube one

of the tricks with Ruby is that if you

don't excite the entire tube with flash

light the rod itself will absorb its own

laser light and then it will stop lazing

so the entire tube needs to be

completely saturated with flash light

one possible way to do this is to get a

straight flash tube and put it near the

Ruby rhod and then put this in an

elliptical enclosure and an ellipse has

two foci inside and if the rod is on one

fossa and the flash tube is on the other

then you polish the inside of this whole

elliptical chamber we'll get good

coupling between the flash tube and the

rod and this can be extended you could

have like a double elliptical chambered

or as many tubes as you want around it

basically but again this particular

flash lamp was just a little too long

and so I'd be losing a good you know

twenty or thirty percent of the flash

length trying to get all the light into

the rod and also this single flash tube

wasn't enough and so I need at least two

of these and even then it probably

wasn't quite enough so luckily I

recently found a pair of these on ebay

and this is a helical flash tube that is

almost the perfect length for this for

this Ruby rod here and it's a little bit

too short but I think that's going to be

okay so if my chamber is reflective on

the inside

we'll get good coverage of flash light

into the into the rod

I've also got specialised mirrors that

are made specifically for Ruby lasers

and they are in these gimbal mounts and

so if I turn the knobs on these mirror

mounts it's adjusting the alignment of

the mirror in a very very fine manner

and the trick is that we align this

whole system with another laser in this

case I've got a helium-neon facing into

it like this and the idea is that we put

a card here with a hole in the card and

then adjust the knobs around so that the

beam goes straight in and then straight

back out and disappears on the card

because it's actually going back into

the laser and once you once the mirrors

are aligned properly like that we know

that we have an optical resonator a

cavity here where the light is just

going to go back and forth between the

two mirrors now the trick is that the

forward mirror is only partially

reflecting and for a ruby laser the gain

is fairly high again because the rod is

so dense so for a helium-neon laser the

gas molecules don't provide all that

much light amplification so the mirrors

are both very reflective the output

mirror is probably 98% reflective so the

light that comes out of a helium-neon

laser is only about 2% of what's being

bounced around inside the cavity for a

ruby laser this is only about 30 percent

reflective so most of the light is

actually leaving the cavity for each

bounce so the idea is we put the Ruby

rod inside the flash tube and support it

with something this is not my final

design this is just a test bed and then

you basically want to construct an

aluminum or metal chamber around the

whole flash tube like this to keep the

light inside so that all the light

generated by the flash system will be

reflected around and go into the Ruby

rhod the electrical system is

surprisingly simple it's basically just

a high voltage supply that's connected

to a capacitor bank and then the

capacitors are wired right across the

flash lamp sort of at all times and then

when we want to make a flash happen we

trigger the flash lamp with this trigger

circuit so there isn't really any

switching device you don't really need a

thyristor or anything like that the

major design trick is to fit

you're out how to operate the flash lamp

in a safe way and also get as much light

out as possible into the Ruby rhod so

one of the tricks with Ruby is that we

only have about a 2 or 3 millisecond

window to pump light into it before it

will start to self emit so with with

laser mediums there's this residence

time where the gain medium will stay

activated before it starts to decay all

by itself and for Ruby I think this is

about 2 or 3 milliseconds which is good

because that means we have actually a

relatively long amount of time to pump

it up with the light from the xenon

flash this system of triggering is

called external triggering and what

happens is if we put a metal or a

conductive substance around the outside

of the tube and then suddenly hit it

with a really fast pulse of high voltage

the electricity will actually

capacitively couple through the quartz

wall of the tube and ionize the gas

inside which is what breaks it down and

allows the arc to strike or allows the

main capacitor bank to discharge there's

other ways to initiate the breakdown -

we could put a coil or a transformer in

this supply line and then inject the

high voltage pulse into the supply line

here and this is known as series

triggering so there's a couple I'll put

a link in the description to this PDF

but there's a couple different ways of

setting up triggering for now I think

I'm going to try to stay with external

triggering since I don't I'm not going

to have a high refresh or a high

repetition rate of flashes I'm going to

try to air cool this tube and when we do

air cooling that's that makes the job a

lot easier for obviously a lot of

reasons one thing to watch out for is

the maximum amount of energy that the

flash tube can take in one shot this is

known as the explosion energy and it's

the lifetime of the two is related to

the percentage at which you run the

explosion energy so obviously he ran it

at 100% it's going to explode in your

lifetime would be one flash you also

don't really want to operate it at 60%

of its explosion energy because you have

a very short life probably you know 100

flashes or something like that so this

chart here helps us calculate what the

explosion energy would be for that tube

and we look up the

diameter which in this case is about 8

millimeters and the pulse duration 1/3

of peak amplitude in milliseconds so

let's say our pulse is going to last one

and a half or maybe two milliseconds we

can look that up on the chart and then

look over and it will tell us how much

energy we can have per length of flash

tube so this comes out to be you know

somewhere on the order of one kilojoule

per inch of flash tube and since this is

a helical flash tube we get to figure

out how long it is just by you know

calculating the circumference and

multiplying by the number of turns and

as it all comes out we end up with about

a 30 kilojoule burst energy or explosion

energy and ideally I want to run this

tube at about eight kilojoule pulses and

so if we use another equation to figure

out what the lifetime would be we end up

with about 76,000 flashes will be pretty

safe operating it at 8 kilojoules as it

happens I found this documentation sheet

in a Perkins Elmer catalog and found a

tube that's very very similar but not

exactly the same as mine and they list

the explosion energy for 1/2 millisecond

pulse at about 20 points something

kilojoules there so it's in the same

ballpark to test out the actual pulse

length I've made this little optical

sensor circuit and what I did is I took

apart a fast photodiode from one of

these little fiber optic connectors and

I'll put a link in the description and

reverse-biased it with this 9-volt

battery and this is a thin piece of coax

that's going off to the scope so what I

do when I'm running a test shot is just

to put this little sensor kind of

anywhere near the flash tube and then

the scope will record the amount of

light hitting the sensor the capacitor

bank can be configured in a lot of

different ways so for example we could

keep putting more and more capacitors in

series to get a higher voltage or we

could put more than in parallel to get a

higher capacitance and the decision I

mean the way that we make that decision

is to figure out what sort of pulse

length we get for a given voltage and

this

just depends upon the tubes impedance

and the inductance if we add any to this

and other internal resistance of the

capacitors it's basically quite an

involved thing and so I'll probably do

some testing as I go along currently

this is only about a tenth of my total

bank capacitance this is maybe six

hundred joules of energy storage here

and the rest of the bank includes way

more these capacitors to bring it up to

a total of about six and a half

kilojoules and then I have another 4.8

kilojoules of caps that I haven't taken

out of this professional photography

unit I'm using this electrophoresis

power supply to charge up the cap bank

and this is pretty convenient because it

will do six kilovolts at a hundred

milliamps which is a lot of power and

voltage and it can also be limited in

charge power in watts so I can set a

limit of say twenty watts and it won't

charge any faster than that which is you

know nice just to sort of keep an eye on

things things won't charge too quickly

to discharge the bank I've got this

really large thick film resistor I tried

using some wire wound resistors but even

despite having power ratings of like 25

watts or something they would just pop

instantly because the peak power is so

high with this one I generally connect a

grounding wire to one side of this and

then draw an arc off the capacitor bank

here so I've started the supply here and

you can see it's charging up and it's

peaking out Hertz it's limiting at about

14 watts of charge and the voltage is

going to come up to about 3000 so this

supply is super handy because I can set

a voltage limit and also a power limit

so now as we approach 3,000 volts the

limit transitions to voltage and it will

maintain this 3000 volt charge in the

bank

so if I were going to discharge it I'm

going to connect the ground lead to the

other side of this resistor here and

then I'm going to turn the supply off

which doesn't actually discharge the

bank internally all it does is

disconnect so to discharge it we

actually draw an arc here

and you can see the voltage is coming

down quite a bit the datasheet that I

found says that tube with this length

has a minimum firing voltage of about

four thousand volts and so I've been

trying other tubes out and I've got this

one - fire sort of irregularly at about

three thousand volts but haven't had the

guts to get a large enough capacitive

bank to do four thousand yet but I will

soon I would show you this thing

flashing but on camera it's not that

exciting because all you see is a single

white frame you can see another video

that I posted where I was showing what a

4.8 kilojoule flash looks like and it

it's just actually not that exciting on

video also these tubes are quartz glass

they are not soda-lime glass and that

means that they pass ultraviolet light

just fine and there's quite a bit of

ultraviolet emitted in the xenon arc so

you have to be careful with these

because they actually will give you a UV

dose if you don't wear eye protection so

I have these which are laser safety

glasses but I'm not sure if these

actually block UV so it'd really be

better just build this into an enclosure

so that none of the xenon arc lamp light

gets out just the laser light which will

be blocked by these okay see you next

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