Would You Believe a 180mW Blu-Ray?

Regarding these power meter questions: I'm going to try to find out if I can use the power meters on campus in the research group I'm in. I'm hesitant to ask because I'm fairly new in the group, and I don't want to break anything or start trying to take personal liberties too early in my position, but this question with the meters at 405nm really deserves an answer.

But I think I can justify it, as these could be of usefulness at times in my group, as they sometimes still have to buy some commercial diodes, and these are a heck of a lot cheaper than "one-offs" from commercials sources. And using the testing units in my group, it would be definitive.

climbak, you have questions about your university-based meter? I would have thought it would be well-calibrated.

I would like to see if I can find any info regarding the 'mechanical' differences of the two sensors (surface vs volume). Obviously from the name we can assume that a surface type calorimeter measures heat from the surface of the sensing medium, but what about the volume sensor? I too believe that the 'slow rise' in mine is partially due to the diode drawing more current as it heats, but I think it is more related to the sensor itself. I just did the same test as you and mine behaved in about the same way as always. It rose to about 175, dropped a bit to around 170, then climbed to 200mW over about 20sec. and it was already warm at this point, so I can pretty much take the laser temp out of the equation.

Interesting stuff!

All this new info has made me curious as to the validity of my measurements. Maybe I'll mail one of you guys with a thermal meter my mxdl build to check it. I have a feeling my reading is a tad high.

EDIT: oh, and the meter I am using is at the lab of the company I work for so I have no clue on the accuracy of the meter. The one in the lab at school is only rated to 20mW since my professor doesnt need a super nice one for the work he does. Most of his lasers run in the 7mW range.

climbak said:

All this new info has made me curious as to the validity of my measurements. Maybe I'll mail one of you guys with a thermal meter my mxdl build to check it. I have a feeling my reading is a tad high.

EDIT: oh, and the meter I am using is at the lab of the company I work for so I have no clue on the accuracy of the meter. The one in the lab at school is only rated to 20mW since my professor doesnt need a super nice one for the work he does. Most of his lasers run in the 7mW range.

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My mailbox is always open for you

Peace,
dave

It is very frustrating having to wait for my sleds from SenKat and AMK....I am itching to play with these LD's....I have hosts and drivers poised for the build....
I am not sure I am going to be as brave as you on the ma front.....well not on the first one anyway

Keep us informed Dave, pushing the envelope is good....(when someone else is paying) :

Regards rog8811

WOW, the 6x should be able to spit 300mW then ;D. I'm still only gonna drive mine at 90mA.

daguin said:

My mailbox is always open for you

Peace,
dave

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I need some more play time with it before I send it off for a week or so haha. I turned the driver all the way up now too, so it is mildly brighter than before and I'll have to test it again.

190mA? Thanks for taking one 'for the team'. My opinion is you'll be lucky to see over 10 hours use from the diode, but what the f*ck do I know. Nice build BTW.

daguin said:

At that time people started getting used to and expecting 100% duty cycles from these diodes. Almost nobody expects this from a hand held red or green or blue or yellow, laser, but somehow they expected it from a violet laser. A couple of fearless enthusiasts were not fettered by these artificial bonds. Milos did some destructive tests. GooeyGus pushed his past the "safe" zone. Climbak has one of these diodes running at 120mA input 24/7 without a good heat sink, under a piece of paper, and it has been running at 100% duty cycle for over a month! I decided to see what these diodes could do.

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If you're not able to get a 100% duty cycle from a direct injection diode (not DPSS) it's a poor design, IMO. Let me qualify that by stating any diode < 200 mW one should be able to come up with a design that's properly heat sinked such that it has no duty cycle. IN most cases it's no more than 1-2 watts of heat that needs be dissipated. The reason most of the lil pen pointers have a duty cycle is the package is too small - not enough thermal mass.

Used to be there was little room with low power diode to drive them overspec. They would simply die. These newer high powered LDs seem much more forgiving of being pushed over spec, however the price seems to be a shorter life. Even if your diode only holds up for a few hours close to 200mW it's a long time if only used 1-2 minutes at a time.

climbak said:

[quote author=daguin link=1214100163/12#19 date=1214122333]

My mailbox is always open for you

Peace,
dave

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I need some more play time with it before I send it off for a week or so haha. I turned the driver all the way up now too, so it is mildly brighter than before and I'll have to test it again.[/quote]


YES!!!!

KILL THEM ALL!!!!!!!

BWAAAAAAAHHHAAAHAHAHAHAHAHAHAHAHAHAHhahahahahahahahahaaaaaaaaaaaaa............. . . . . . . . . . . .

Peace,
dave

daguin said:

I believe HemlockMike reported that as these heat up, they begin to draw more power as well.

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Mike did report the current climbing with heat. But it's not really true the way it was put here..

Mike is/was using a constant voltage source for his 6x diode. When diodes heat up their internal resistance decreases.. If you are driving a diode with a constant voltage, at which the current is 180mA, the heat will make the resistance drop and the current will go up. This is true for all diodes, not just blu(e) rays..

But if you're driving it with a constant current source, the driver will not let that happen. A constant current driver always gives a load just enough voltage for a certain current to flow. So when the diode heats up and the resistance drops, the driver will reduce the voltage, and the current is going to stay the same..


So:
Constant voltage + heat = current up (voltage stays the same - input power goes up)
Constant current + heat = voltage down (current stays the same - input power goes down)


This is the reason we use (or should use) constant current drivers. The current can not change on it, unless there is something wrong with the driver..
Using constant voltage results in a climbing current. More current means more heat, more heat less resistance, more current, more heat and so on - which can ultimately result in a thermal runaway and a dead diode.

180mA!?!??! Well, time to crank up the current to 135mA.... Right now it is set to 125mA, and it is significantly brighter than it was at 90mA.
I wonder what the power would be at 135mA if we use one of IgorT's 405nm Coated lenses.

We will know that soon enough.. It's impossible to tell exactly, because we don't even know how much power the diode alone produces at that current - this measurement is hard to make reliably.

I have some expectations, but i don't want to make guesses anymore. What i do know is, that the lens will bring as much as possible for a lens. The transmittance of good lenses is usually 95%, so it only depends on the diode. When i get the transmittance data, and make some measurements, this will also tell us what the diode is actually producing.

IgorT said:

We will know that soon enough.. It's impossible to tell exactly, because we don't even know how much power the diode alone produces at that current - this measurement is hard to make reliably.

I have some expectations, but i don't want to make guesses anymore. What i do know is, that the lens will bring as much as possible for a lens. The transmittance of good lenses is usually 95%, so it only depends on the diode. When i get the transmittance data, and make some measurements, this will also tell us what the diode is actually producing.

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When can we expect results?

Hmm... I don't know...

When i get them maybe? :

IgorT said:

Hmm... I don't know...

When i get them maybe?  :

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And when is that? :

Read the correct thread. If i know, it's there, if it's not there, i don't know.