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.

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Transcript for Laser Beam Expanders Decoded

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0:00 welcome to another session with my

0:02 little tangerine tiger

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

0:05 you for another couple of three weeks

0:07 but things have moved on a little bit

0:10 when i finished filming last time i

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

0:16 about

0:16 the problem that we’d found

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

0:22 fairly small beam two millimeters

0:23 diameter

0:24 and yet at 1.3 meters away

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

0:31 to about 10 millimeters or more

0:34 that can’t be right surely

0:38 anyway i did quite a lot more digging

0:42 in different areas and let me just show

0:44 you some of the stuff that i’ve

0:45 discovered

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

0:48 of this stuff already

0:49 it’s the research and the

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

0:54 wrong that makes it interesting now

0:57 we’ve never noticed

0:58 this problem before on a co2 laser well

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

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

1:05 on a co2 laser

1:07 when the beam exits from the tube

1:10 it has a certain diameter in this case

1:13 it’s

1:13 five millimeters for this c70 model tube

1:16 that i’ve got on that

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

1:20 ordinary glass tube

1:21 model cr70 but it’s an spt tube

1:25 model c70 with this specification

1:28 the beam divergence angle is

1:32 specified here as 3.1 milli radians

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

1:37 what a milli radian is

1:39 but let’s just say that it is a

1:41 measurement of the

1:43 angle of what they call here divergence

1:46 in other words the beam is growing but

1:47 it has an included angle

1:49 of 3.1 milli radians

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

1:55 or equal to 1.1

1:57 m squared now this m squared value is

2:00 basically a definition of the quality of

Transcript for Laser Beam Expanders Decoded (Cont…)

2:02 the beam

2:03 in relation to a true gaussian

2:06 distribution

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

2:11 looking around

2:12 at what this rf laser is capable of

2:15 doing

2:15 [Applause]

2:17 and i find several rather interesting

2:19 facts

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

2:23 the m squared beam quality is 1.2

2:26 it’s not as close to a gaussian

2:27 distribution as our glass tube

2:29 and the beam diameter is 1.8 plus or

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

2:35 call it two millimeters for round

2:36 numbers

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

2:41 then we look at this thing here called

2:43 beam divergence angle

2:45 and remember what it was before 3.1

2:48 milli radians

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

2:54 wider angle what does that mean in

2:57 reality

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

2:59 produce a a nice little scaled

3:02 drawing and basically for this machine

3:06 look the first mirror here is at about

3:09 300 millimeters away from the laser

3:11 and the other extreme right down at the

3:13 other end of the machine

3:15 is around about 1.3 meters away

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

3:21 a complete

3:23 moving beam in there because the last

3:25 six or eight inches of that beam for

3:27 instance

3:28 is beyond mirror three which is

3:30 completely static so we’ve got 500

3:32 millimeters of movement here and 300

3:34 millimeters of movement here roughly

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

3:38 a

3:39 rf tube beam we start off

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

3:46 is

3:46 say four millimeters diameter and by the

3:49 time we get to the front corner that

3:50 beam has grown

3:52 to over 11 millimeters diameter by the

3:54 time it gets to hitting the lens

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

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

Transcript for Laser Beam Expanders Decoded (Cont…)

4:01 something like about 280 percent change

4:04 something like that whereas with the

4:06 glass tube

4:09 we start off at a five millimeter beam

4:11 and it grows from

4:13 six millimeters to say nine millimeters

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

4:20 on a five millimeter beam

4:26 and that’s only about 50

4:30 among friends so there is a huge

4:33 difference

4:34 in the performance of these raw beams

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

4:41 mentioned in the last session

4:42 that cloud ray sent me something along

4:46 with this laser tube they sent this

4:50 thing

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

4:52 in that end

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

4:56 called

4:56 be for beam expander

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

5:03 last session

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

5:06 that on its own

5:08 what we really need is something called

5:10 a collimator

5:11 which basically turns the rays back into

5:13 a parallel path

5:15 rather than a diverging path i went away

5:18 and did

5:18 a little bit more reading and research

5:21 onto

5:21 beam expanders and it appears that what

5:24 i’ve got here

5:26 is probably going to solve the problem

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

5:33 is definitely only called a beam

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

5:36 done

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

5:39 are

5:40 that it’s going to perform something

5:42 like this

5:44 [Applause]

5:48 our expanding beam comes into one lens

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

5:55 larger diameter

5:57 and then come out and then comes out

5:59 this end as a parallel

Transcript for Laser Beam Expanders Decoded (Cont…)

6:01 set of rays okay so

6:05 this is what the expansion bit is this

6:07 is basically

6:08 an expander and a collimator in one

6:11 piece of kit

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

6:16 about this

6:17 anywhere i’ve been to the coherent

6:19 website they mentioned these beam

6:21 expander collimator

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

6:25 actually mention it

6:27 and they do say that look this number

6:29 here three times three x

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

6:33 to take this input beam

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

6:37 to expand it out

6:39 and turn it into a parallel beam which

6:41 will be

6:42 three times the size of the start beam

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

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

6:48 a parallel

6:49 six millimeter beam coming out of here

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

6:55 that’s to try it so

6:56 undoubtedly this has got to fit on here

6:59 somewhere

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

7:04 expecting to find

7:07 um i was expecting to find

7:10 an m22 thread on there as well

7:15 so that i could just go

7:18 like that and screw it on i mean

7:21 presumably this must be standard for

7:24 this sort of system so

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

7:28 special adapter plate

7:29 with an m22 thread in it that screws

7:32 onto there

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

7:35 ask cloud ray

7:37 if they have such an adapter plate which

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

7:41 the meantime i think we need to test

7:43 this quickly

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

7:46 with my

7:47 cad system and design something that

7:50 will hold this

7:52 just there well here we are about an

7:54 hour and a half later

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

7:59 ourselves something from acrylic

Transcript for Laser Beam Expanders Decoded (Cont…)

8:01 my favorite material and what does it do

8:06 well that plugs in there

8:10 and that thread just pushes into

8:14 the back dumbbell it does fit in there

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

8:18 there are not adequate dimensions to

8:20 make this thing

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

8:23 or i’ve been able to track down

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

8:30 lens to the laser beam

8:32 axis now this time in the interest of

8:34 being nice and consistent

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

8:41 into this

8:42 laser set mode down here

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

8:48 continuous

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

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

8:54 to put a 20

8:55 millisecond pulse so i’ve got a

8:58 consistent pulse that i’m firing

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

9:07 a nice piece of white card here

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

9:11 it’s not going to catch fire

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

9:15 that on the

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

9:18 150 millimeters

9:20 beyond the end of that beam experiment

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

9:24 machine now

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

9:28 we’ve changed it now to

9:29 50 milliseconds and that’s what a 50

9:33 millisecond pulse looks like now we’re

9:35 at one point three

9:36 thirteen hundred millimeters away

9:40 and we’ve given another fifty

9:42 millisecond pulse

9:48 nothing

9:51 two three four

9:55 five six seven eight nine

9:59 ten eleven twelve

Transcript for Laser Beam Expanders Decoded (Cont…)

10:05 so let me be fair about this

10:18 you can’t make it any bigger

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

10:24 clearly that

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

10:28 before we’ve got

10:30 a much smaller uh divergence in the beam

10:33 between 1300

10:35 and 150 i think we can fairly

10:37 comfortably conclude

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

10:41 ray

10:41 called a beam expander is

10:44 an expander and a collimator that

10:46 certainly answered quite a few questions

10:48 for me

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

10:52 clear

10:53 for when we start next time so until

10:56 then

10:57 thanks for your patience and time again

Transcript for Laser Beam Expanders Decoded


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