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Thread: Modulating a laserwave 150mW 532 dpss

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    Laser Warning Modulating a laserwave 150mW 532 dpss

    For those of you who are interested in modulation characteristics of dpss lasers, I did some measurements. Channel 2: 1 division equals 100mW
    equiment used: tektronix tds 210, AN2 ophir power meter, bpw34 photo diode
    Minimal 1 hour stabilisation time on infinite heatsink.

    TTL input square wave 100mHz
    TTL input square wave 1Hz
    TTL input square wave 10Hz
    TTL input square wave 100Hz
    TTL input square wave 1kHz
    TTL input square wave 10kHz
    TTL input square wave 50kHz

    TTL input square wave burst 8x 500uS 10Hz repetition rate
    TTL input square wave burst 8x 500uS 100Hz repetition rate
    TTL input square wave burst 8x 50uS 100Hz repetition rate
    TTL input square wave burst 8x 5mS 1Hz repetition rate

    Analog input linearity response at 1kHz typical ramp sample
    Analog input linearity response at 1 kHz average of 128 ramps

    Analog input sine modulation 1kHz, no dc offset.
    Analog input triangle modulation 1kHz, no dc offset.

    Analog input sine modulation 10Hz, dc offset to compensate for modulation offset.
    Analog input sine modulation 100Hz, dc offset to compensate for modulation offset.
    Analog input sine modulation 1kHz, dc offset to compensate for modulation offset.
    Analog input sine modulation 10kHz, dc offset to compensate for modulation offset.

    I did some pulse width modulation tests too, output power is linear in respect to the duty cycle <80%.
    But the results I obtained over 80% dutycycle were unstable.
    Output power had a hard time stabilizing >80%

    Despite the general opinion that Chinese dpss lasers modulate badly, I think this one does pretty well.
    The only thing is does badly is running *unmodulated*. When a new dc voltage is applied, in relatively big steps (>2Volts) , it takes seconds to minutes to stabilize at this new power.

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    Nice test Bart,

    I have just received 2x 500mW viasho lasers, the warmup curve and stability is impressive I think.

    Within 3 minutes they reach maximum power and they are stable withing 0.1%.

    Compared to the laserwave 500mW I tested they needed minum 10-15minutes to warmup.

    Maybe its interesting to add the viasho also to the test so we have comparisation between different brands.

    If you want I can bring my viasho to you for test.

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    Interesting test! I wouldn't mind some additional experimental details. For example, did you have any filters in front of the photodiode and how was it hooked up to the oscilloscope?

    I would also be interested in the response at even lower frequencies, as I can certainly see how laser shows contain such components. What does the response look like at for example 10 mHz? My own laserwave has severe problems with stability at this frequency, to the point that it ruins any attempts at color balance.

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    . For example, did you have any filters in front of the photodiode and how was it hooked up to the oscilloscope?
    The pd was connected in series with a 10k resistor to 24volts.
    No filters, I concluded earlier that there was hardly any ir leakage.
    Then I tried a polaroid filter as a variable attenuator, but was hard to align well.
    So I omitted the extra filters.
    I used a knife edge mirror to direct just as much light onto the pd that it corresponded with 100mW/div.
    I directed the remaining part of the beam onto a thermal power meter.

    I did some 10mHz measurements too, but the results are different every time. So I chose not to publish them. The 100mHz results are pretty reproducible.

    My scope might not be slow enough to capture 100 seconds on one screen.
    I could do a 1Hz acquisition with my rms multimeter, for some hours, modulating the laser at 10mHz.
    Then average out some 100 periods of 100seconds. That may be a fair test to compare it side by side with other lasers.

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    Interesting results indeed! I'm curious how you managed to get such a clean pulse at 100MHz when that driver most likely can't be modulated past 40kHz on a good day.. Are you bypassing the driver and powering the diode with a different supply? Or are the published driver max. modulation rates completely inaccurate, instead allowing MHz range modulation rather than kHz (quite possible given the Chinese penchant for less than accurate specs)?

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    That's mHz nót MHz

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    Ok.. whether it's mHz or MHz, it still doesn't make any sense. 1 milliHertz is 1/1000 of 1Hz, which is an incomplete wave. Even 100 milliHertz is an incomplete wave. In order to have a complete wave, the frequency must equal 1Hz or more.. So obviously 1m(illi)Hz makes no sense.
    Last edited by ElektroFreak; 01-19-2010 at 07:24.

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    Maybe he means a frequency of .1hertz (10 second pulse duration with a 50/50 duty cycle) and he's using the metric prefix of milli? That's the way I interpreted it anyway. (Though I agree that it's absolutely *not* a standard way of stating frequency.)

    Adam

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    hmm.. I didn't think of it that way. That must be it..

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    Quote Originally Posted by buffo View Post
    Maybe he means a frequency of .1hertz (10 second pulse duration with a 50/50 duty cycle) and he's using the metric prefix of milli? That's the way I interpreted it anyway. (Though I agree that it's absolutely *not* a standard way of stating frequency.)

    Adam
    Probably the display on a fancy signal gen reads milli....

    Steve
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