Square glass on a laser diode and beam issue

Hi there,
I took a diode from a dvd burner drive and it found a small square glass on it. Its maybe 2x1 mm.
It looks like this http://s3.postimage.org/8w9q34wlf/400486111_727.jpg
I noticed that the laser diode with that glass transmitts a large red line on the wall, not a circle. When I was putting the diode in the module I accidentally torn the off glass so now the laser emits a large red circle. I'm interested in what was the purpose of the glass. I also have a problem with the laser beam, the burning focus is not a problem, but I can not get a beam with a long narrow line of light. When foucus it to burn things the line is then narrow only about 2 meters, after that then it greatly expands. And when I try to adjust it to be narrower at longer distances, it is pretty large the first few meters (example: i point it to a wall aprox. 5 meters from me, the dot is maybe 4 cm in diameter at 1 meter, then it gradualy gets smaller). It behaves like a hybrid of a laser and a flashlight :undecided:
So my questions are:
1. What is the purpose of additional square glass on the diode?
2. Could i get a better beam when I managed to get the glass back in place?
2.a. How to do that without damaging the diode?
3. Possible reasons why I can not get a narrow beam of light?
Thanks ahead guys
p.s. i have bought this cheap module with focusable lens Red Laser Module - Focusable Dot (3.5V~4.5V 11.89mm 5mW) - Free Shipping - DealExtreme
p.p.s. sry for the bad pic, it was taken from a cell phone, and it does not have a good macro

The small piece of glass was more than likely a form of beam splitter. It would allow a greater majority of power to pass through it, while maybe 5% of the power would be reflected onto a sensor of sorts to allow the drive to accurately maintain a certain power output.

OR, it could have been the IR/red laser beam combiner...

is it half-barrel shaped? like a round rod cut in half down the middle?

it sounds like that tiny lens really helped shape the beam.

pschlosser said:

is it half-barrel shaped? like a round rod cut in half down the middle?

it sounds like that tiny lens really helped shape the beam.

Click to expand...

It does not look like that, its just a flat square.

slam a hammer on it

@weeba2kv Why do you post something so useless?

@OP I also think it is some sort of lens to help focusing the laser, OR if there is no window left on the diode (assuming the little glass thingy acted as the window), it could be some dirt or dust that came inside the can, spoiling the output OR I have seen that the diode used for reading the CD or DVD, was in a module that had no lens, It was basically just a diffraction grating making a line consisting out of dots, like this:

. . . . . . . . . . . . . . . .

Maybe a similar diffraction grating was mounted directly onto the diode, and was not meant to be focused in a tight beam.

Just my two cents...

Cube777 said:

@weeba2kv Why do you post something so useless?

@OP I also think it is some sort of lens to help focusing the laser, OR if there is no window left on the diode (assuming the little glass thingy acted as the window), it could be some dirt or dust that came inside the can, spoiling the output OR I have seen that the diode used for reading the CD or DVD, was in a module that had no lens, It was basically just a diffraction grating making a line consisting out of dots, like this:

. . . . . . . . . . . . . . . .

Maybe a similar diffraction grating was mounted directly onto the diode, and was not meant to be focused in a tight beam.

Just my two cents...

Click to expand...

Well the diode still has its glass, the square one was the second one, any sugestions why the beam is not narow

Cube777 said:

@weeba2kv Why do you post something so useless?

Click to expand...

He's gotta get his post count up somehow!

@OP As others have said, It's most likely a beam splitter.

@OP Can you tell if there was a lens in front of the diode when it was in the sled?

Billiam said:

He's gotta get his post count up somehow!

@OP As others have said, It's most likely a beam splitter.

Click to expand...

That anwsered the first two questions, one more to go...

Cube777 said:

@OP Can you tell if there was a lens in front of the diode when it was in the sled?

Click to expand...

I think not, there where two mirrors and a prism shaped glass, the usual stuff in a dvd burner, this tiny square glass was glued on the diode

^If there was no lens, that laser was never meant to be focused. I think that diode was not meant to burn DVDs, like I said, previously I was in a similar situation with a diffraction grating generating a line, that is most likely a diode meant to read, not burn (and not focused). If you have another laser shine it through the little piece of glass and look if it generates a line or something similar.

A have fixed it, the diode was not properly installed . This is my first laser build so you can understand how this happened.
Thanks guys