06 – Laser Beam Expanders Decoded

The Tangerine Tiger Series with Russ Sadler

In this Series, Russ has purchased a new 500 x 300mm, 50W laser machine from eBay with a view to modifying and upgrading it. In fact, he rips out the glass laser tube and high voltage power supply and replaces them with an RF laser source and PSU from Cloudray. Watch how Russ attempts to understand how Laser Beam Expanders works and fits one to the RF laser source!

Laser Beam Expander and The Tangerine Tiger Working Range
Laser Beam Expander and The Tangerine Tiger Working Range

If you are considering purchasing a CO2 laser machine with an RF laser source from one of the big boy suppliers, I would suggest you check out this series before making a decision!


A quick footnote to the last session where the discovery of a rapidly expanding laser beam brought home the importance of understanding what technical parts of the specification actually mean in the real world.

Previous VideoNext VideoSeries Menu

Video Resource Files for Laser Beam Expanders Decoded

There are no more resource files associated with this video.

External Resource Links for Laser Beam Expanders Decoded


There are no more external resource links associated with this video.

Transcript for Laser Beam Expanders Decoded

Click the “Show More” button to reveal the transcript, and use your browsers Find function to search for specific sections of interest.

0:00welcome to another session with my

0:02little tangerine tiger

0:03now i promised you i wasn’t going to see

0:05you for another couple of three weeks

0:07but things have moved on a little bit

0:10when i finished filming last time i

0:13stopped and had a bit of a serious think


0:16the problem that we’d found

0:20and that was that we start off with a

0:22fairly small beam two millimeters


0:24and yet at 1.3 meters away

0:28which is not very far the beam had grown

0:31to about 10 millimeters or more

0:34that can’t be right surely

0:38anyway i did quite a lot more digging

0:42in different areas and let me just show

0:44you some of the stuff that i’ve


0:46it wouldn’t be interesting if i knew all

0:48of this stuff already

0:49it’s the research and the

0:52wondering whether or not i’ve got it

0:54wrong that makes it interesting now

0:57we’ve never noticed

0:58this problem before on a co2 laser well

1:01it turns out there’s a jolly good reason

1:03why we haven’t seen this problem before

1:05on a co2 laser

1:07when the beam exits from the tube

1:10it has a certain diameter in this case


1:13five millimeters for this c70 model tube

1:16that i’ve got on that

1:18laser machine over there it’s just an

1:20ordinary glass tube

1:21model cr70 but it’s an spt tube

1:25model c70 with this specification

1:28the beam divergence angle is

1:32specified here as 3.1 milli radians

1:36i’m not going to go into the maths of

1:37what a milli radian is

1:39but let’s just say that it is a

1:41measurement of the

1:43angle of what they call here divergence

1:46in other words the beam is growing but

1:47it has an included angle

1:49of 3.1 milli radians

1:52it also has a beam quality of less than

1:55or equal to 1.1

1:57m squared now this m squared value is

2:00basically a definition of the quality of

Transcript for Laser Beam Expanders Decoded (Cont…)

2:02the beam

2:03in relation to a true gaussian


2:07so 1.1 is pretty good so then i start

2:11looking around

2:12at what this rf laser is capable of



2:17and i find several rather interesting


2:21first of all the beam quality is not 1.1

2:23the m squared beam quality is 1.2

2:26it’s not as close to a gaussian

2:27distribution as our glass tube

2:29and the beam diameter is 1.8 plus or

2:33minus 0.2 of a millimeter and let’s just

2:35call it two millimeters for round


2:37um as it exits the rf lace-up window

2:41then we look at this thing here called

2:43beam divergence angle

2:45and remember what it was before 3.1

2:48milli radians

2:50now it’s 7.5 in other words it’s a much

2:54wider angle what does that mean in


2:58well i got to work with mccad system to

2:59produce a a nice little scaled

3:02drawing and basically for this machine

3:06look the first mirror here is at about

3:09300 millimeters away from the laser

3:11and the other extreme right down at the

3:13other end of the machine

3:15is around about 1.3 meters away

3:19from the start point now we haven’t got

3:21a complete

3:23moving beam in there because the last

3:25six or eight inches of that beam for


3:28is beyond mirror three which is

3:30completely static so we’ve got 500

3:32millimeters of movement here and 300

3:34millimeters of movement here roughly

3:36the essence of this story is when we use


3:39rf tube beam we start off

3:42here at the back corner with a beam that


3:46say four millimeters diameter and by the

3:49time we get to the front corner that

3:50beam has grown

3:52to over 11 millimeters diameter by the

3:54time it gets to hitting the lens

3:56so that’s a that’s a massive change

4:00in fact i think i worked it out at

Transcript for Laser Beam Expanders Decoded (Cont…)

4:01something like about 280 percent change

4:04something like that whereas with the

4:06glass tube

4:09we start off at a five millimeter beam

4:11and it grows from

4:13six millimeters to say nine millimeters

4:17so we’ve got a three millimeter growth

4:20on a five millimeter beam

4:26and that’s only about 50

4:30among friends so there is a huge


4:34in the performance of these raw beams

4:39so what can we do about it as i

4:41mentioned in the last session

4:42that cloud ray sent me something along

4:46with this laser tube they sent this


4:50what is this thing well it’s got a lens

4:52in that end

4:53it’s got a lens in that end and it’s


4:56be for beam expander

5:00now as i cynically said to you in the

5:03last session

5:04we don’t need a beam expander it’s doing

5:06that on its own

5:08what we really need is something called

5:10a collimator

5:11which basically turns the rays back into

5:13a parallel path

5:15rather than a diverging path i went away

5:18and did

5:18a little bit more reading and research


5:21beam expanders and it appears that what

5:24i’ve got here

5:26is probably going to solve the problem

5:30i say probably i don’t know because this

5:33is definitely only called a beam

5:35expander but from the reading that i’ve


5:37if it’s got two lenses in it the chances


5:40that it’s going to perform something

5:42like this


5:48our expanding beam comes into one lens

5:51at this end it gets expanded to a much

5:55larger diameter

5:57and then come out and then comes out

5:59this end as a parallel

Transcript for Laser Beam Expanders Decoded (Cont…)

6:01set of rays okay so

6:05this is what the expansion bit is this

6:07is basically

6:08an expander and a collimator in one

6:11piece of kit

6:13i think but i can’t find any information

6:16about this

6:17anywhere i’ve been to the coherent

6:19website they mentioned these beam

6:21expander collimator

6:23systems they don’t show me one but they

6:25actually mention it

6:27and they do say that look this number

6:29here three times three x

6:31on the end probably means that i’m going

6:33to take this input beam

6:35which is two millimeters and i’m going

6:37to expand it out

6:39and turn it into a parallel beam which

6:41will be

6:42three times the size of the start beam

6:44so that’s going to be six millimeters

6:46so hopefully we may find that we’ve got

6:48a parallel

6:49six millimeter beam coming out of here

6:53and there’s only one way to find out and

6:55that’s to try it so

6:56undoubtedly this has got to fit on here


7:01it’s got an m22 thread on it and i was

7:04expecting to find

7:07um i was expecting to find

7:10an m22 thread on there as well

7:15so that i could just go

7:18like that and screw it on i mean

7:21presumably this must be standard for

7:24this sort of system so

7:26it’s a possibility that there is a

7:28special adapter plate

7:29with an m22 thread in it that screws

7:32onto there

7:33to hold it i’m going to have to probably

7:35ask cloud ray

7:37if they have such an adapter plate which

7:40they haven’t sent me but of course in

7:41the meantime i think we need to test

7:43this quickly

7:44and so i’m going to just scrabble around

7:46with my

7:47cad system and design something that

7:50will hold this

7:52just there well here we are about an

7:54hour and a half later

7:57and look what we’ve got we’ve made

7:59ourselves something from acrylic

Transcript for Laser Beam Expanders Decoded (Cont…)

8:01my favorite material and what does it do

8:06well that plugs in there

8:10and that thread just pushes into

8:14the back dumbbell it does fit in there

8:16snugly so it’s not going to fall out

8:18there are not adequate dimensions to

8:20make this thing

8:21from the literature that i’ve been sent

8:23or i’ve been able to track down

8:27so hopefully it’s reasonably true to the

8:30lens to the laser beam

8:32axis now this time in the interest of

8:34being nice and consistent

8:38what i’m going to do i’m going to go

8:41into this

8:42laser set mode down here

8:46enter i’m going to change that away from


8:50and turn it onto manual and now i’m

8:53going to jump down to here and i’m going

8:54to put a 20

8:55millisecond pulse so i’ve got a

8:58consistent pulse that i’m firing

9:00now we turn the laser on hold your ears

9:07a nice piece of white card here

9:09which got lots of china clay in it so

9:11it’s not going to catch fire

9:12it just marks up nicely and we’ll put

9:15that on the

9:16end of the machine here and that’s about

9:18150 millimeters

9:20beyond the end of that beam experiment

9:23you’re around the noisy side of the

9:24machine now

9:26so you can see what’s going to mark now

9:28we’ve changed it now to

9:2950 milliseconds and that’s what a 50

9:33millisecond pulse looks like now we’re

9:35at one point three

9:36thirteen hundred millimeters away

9:40and we’ve given another fifty

9:42millisecond pulse


9:51two three four

9:55five six seven eight nine

9:59ten eleven twelve

Transcript for Laser Beam Expanders Decoded (Cont…)

10:05so let me be fair about this

10:18you can’t make it any bigger

10:22it’s not perfect but i think you’ll see

10:24clearly that

10:26these are not as far apart as they were

10:28before we’ve got

10:30a much smaller uh divergence in the beam

10:33between 1300

10:35and 150 i think we can fairly

10:37comfortably conclude

10:38that that tube that i was sent by cloud


10:41called a beam expander is

10:44an expander and a collimator that

10:46certainly answered quite a few questions

10:48for me

10:49and uh i think it leaves the air fairly


10:53for when we start next time so until


10:57thanks for your patience and time again

Transcript for Laser Beam Expanders Decoded

What Next?

Did you enjoy this post? Why not check out some of our other posts:

DMCA.com Protection Status Follow @laseruser_com