Argon Ion laser vs back reflexions ... experience feedback

Usage, assemblance and modifications of gaslasers.
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Argon Ion laser vs back reflexions ... experience feedback

Beitrag von smartcut » Mi 27 Sep, 2017 10:20 pm

Hi everyone !

Using a Spectra-Physics mod. 177, 488 nm argon ion laser for personal biological R&D (I'm working on phototherapy by laser light ...), I had recently to build a special simple device to count bacterias using scattered light measurement (90°) through a rectangular quartz tube containing a bacterial culture broth.

As the bacteria concentration for my experiment is low, I need a very stable laser source to improve S/N ratio.

This argon laser is rated for +/- 1% power stability.

The laser tube is new.

The laser beam delivery is performed via a kineFlex 3 m mono mode fiber system.

Unfortunately, during the tests, the laser output was very unstable and I worked on that issue during two months ! (well, during my free time ...).

I finally understood that this laser was very sensitive to back reflexions …

In fact, the back reflexions were involved at two locations : at the input fiber coupler and on the test tube input wall.

I solved the input coupler issue simply by revolving the coupler by a 90° turn. So the polarized back reflexions were not able to re-enter the Brewster window of the laser cavity.

To solve the back reflexions issue due to the test tube (even through the 3 m fiber !), I imagine at first to purchase an optical isolator … a quite expensive device.

Finally, I solved the problem in lowering the laser output power from 40 to 20 mW.

So accordingly, I have to work with a more concentrated bacteria broth, I have to dilute after my measurement for use.

So, be aware of back reflexions : in some situations, they can even damage the laser ... :oops:


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