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Repair of a partially dead LD

Simonas

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So i was by building a michaelson interferometer it was working very well but after 10 mins of operation i started seeing some decrease in beam quality, it started getting grainy. I didn't realise that the insides were starting to burn because some of the beam was reflecting back in to the LD. Then it started getting dimmer every second so i shut it off and this is what i saw:IMG_20200906_182347.jpg

There was a tiny burn mark on the LD!
So i started to thing what could i do to prevent further damage.
So i decided to remove the burning front glass along with the can.
I used a dremel to carefully Make the edges of the can thinner and then i just
pulleIMG_20200906_193536.jpgd the can off with pliers.







So next i presses it back in and it worked!










IMG_20200906_195324.jpg

Although its output power was approx. 200mw out of the original 1w. I still call this repair a success because i managed to save the LD and prevent further damage.
 



Anthony P

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Just curious, what diode are you using? It is my understanding that there are very very few that can be used for interferometry due to coherence length.
 

FireMyLaser

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Doesn't green/blue/violet laser dies degrade in normal atmosphere?
 

Simonas

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I used the NDB7412T. I know its not a single mode diode, has horrible beam specs and so on... (But is SUPER cheap i paid 10 usd for mine) I just wanted to see if my setup is gonna work. well it did work and now i know that using an LD that has output power over 100-300mw is gonna burn without using some extra optics.
Here is the setup with a 660nm LD.IMG_20200904_184639.jpgIMG_20200904_184916.jpg
 

kecked

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Can you show the layout of the system? Curious to see how you implemented it. That’s Really nice pattern.
 

Simonas

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I just just the classical 2 mirror 1 beam splitter setup.but of course to het that nice pattern i had to tune The mirrors for 5 hours because i just used paper shims to get the leveling right.600px-Michelson_interferometer_fringe_formation.svg.png
 

kecked

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Good work. That’s why I asked. I have spent whole weekends trying to get it right. I used motorized mirrors on a setup and that only took 30 min. Unfortunately I didn’t own them. I worked on an IR spec that used fiber to form the interference pattern. It was used as a reference for setting up the spec. It was a solid block so I don’t know what was inside. very Stable. Good spec. I guess it was a split fiber?

hows this for alignment! Not mine.
 

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Simonas

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Good work. That’s why I asked. I have spent whole weekends trying to get it right. I used motorized mirrors on a setup and that only took 30 min. Unfortunately I didn’t own them. I worked on an IR spec that used fiber to form the interference pattern. It was used as a reference for setting up the spec. It was a solid block so I don’t know what was inside. very Stable. Good spec. I guess it was a split fiber?

hows this for alignment! Not mine.
Holy S**T! that's a lot of work. It probably took months ir even years to align everything.
 

Simonas

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Doesn't green/blue/violet laser dies degrade in normal atmosphere?
I think the degradation started, today i measured the LD powrer output and it has dropped by 50mw so i think what you're saying is true. It will probably die in the following months.
 

FireMyLaser

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I have a possibly decade old 1w 445nm diode that I had to decan due to its window breaking. I never ended up using it after that, but now I tested it and its threshold current has gone up from the typical ~250mA to 480mA. I have no idea of how much power it puts out.
But I think this shows how decanning can affect the characteristic of a diode that just sits in storage. It was stored in a zip-lock bag and nothing else to prevent moisture ingress.
 

Simonas

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I have a possibly decade old 1w 445nm diode that I had to decan due to its window breaking. I never ended up using it after that, but now I tested it and its threshold current has gone up from the typical ~250mA to 480mA. I have no idea of how much power it puts out.
But I think this shows how decanning can affect the characteristic of a diode that just sits in storage. It was stored in a zip-lock bag and nothing else to prevent moisture ingress.
But now when i think about it... There are sellers selling laser diodes with a ball lens and in order to fit the LD in to an Aixiz module one must de-can the LD. So it means that its power will drop overtime, so if i were to build a laser pointer with such an LD in a few years it would turn in to a pile of trash.
 

FireMyLaser

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It can be that not all diodes are made the same way, and I know very little of how green diodes behave, or if they can be compred to blue or violet. But I know others have reported issues with performance after decanning blue/violet diodes before before.
 

Lifetime17

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But now when i think about it... There are sellers selling laser diodes with a ball lens and in order to fit the LD in to an Aixiz module one must de-can the LD. So it means that its power will drop overtime, so if i were to build a laser pointer with such an LD in a few years it would turn in to a pile of trash.
Hi,
That is not true sorry the ball lens diodes seat and press in a AiXiz 12mm copper module very well. I have done this a number of times with no issues. The only down side is we cant use a collimating lens to focus the beam. Then we must decan the diode to accomplish that.
Rich:)
 

Simonas

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Hi,
That is not true sorry the ball lens diodes seat and press in a AiXiz 12mm copper module very well. I have done this a number of times with no issues. The only down side is we cant use a collimating lens to focus the beam. Then we must decan the diode to accomplish that.
Rich:)
Yes i forgot to mention that you can press it in but then there is problems with the lens. Glad you corrected me.
 




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