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About DLP3000 by using NIR femto second pulse laser

k.s
Prodigy 90 points

Hello, TI 2E all

We are examining to use a NIR pulse laser for DLP3000.

I have two questions.

1: By using the NIR pulse light, does DLP brake by heat?

2: What is main factor of reducing an optical efficiency by using NIR? (reflection by AR coating? or absorption by covered glass?)

[specification of light source]

wavelength: 1500nm

average power: 50mW

repetition rate: 250MHz

pulse width: 25nm

 

Please tell us these problems.

sincerely.

 

  • 0
    TI__Mastermind 43095 points

    Hello K.S.,

    To answer question # 1 I need to make some clarifications on question #2:

    • I assume that 50 mW is the time averaged power over the area of the beam.  Is this correct?
    • The subject says "femtosecond laser", but you list the pulse width as 25 "nm".  Pulse width is usually the duration in time of the laser pulse, which I then take to be 25 ns (or is it 25 fs?).  Please verify this value.
    • What is the beam profile and diameter?  Example - Gaussian beam 5mm in diameter, or top-hat profile with 7mm diameter.

  • 0 in reply to Fizix
    Prodigy 90 points

    Thank you for your response.

    • I assume that 50 mW is the time averaged power over the area of the beam.  Is this correct?

           →Yes. This understanding is correct.

    • The subject says "femtosecond laser", but you list the pulse width as 25 "nm".  Pulse width is usually the duration in time of the laser pulse, which I then take to be 25 ns (or is it 25 fs?).  Please verify this value.

           →I was miss writing. Please ignore this description.

    • What is the beam profile and diameter?  Example - Gaussian beam 5mm in diameter, or top-hat profile with 7mm diameter.

           →Gaussian beam about 3mm in diameter.

    Perhaps, by AR coating for visible light of DLP3000, is there is no need to consider the above-mentioned concerns?

    (NIR light is reflected by AR coating, therefore, DMD is not absorb heat.)

    Is this understanding correct?

    sincerely,

  • 0 in reply to k.s
    TI__Mastermind 43095 points

    Hello K.S.,

    I calculate that a 50 mW average power, 3mm diameter beam at 250 MHz repetition rate gives an peak energy density of about 5.7 nJ/cm2 at the center of the beam (about 300 nJ total energy per pulse). I do not know what the peak power density per pulse is without knowing the pulse duration.

    The NIR window is optimized for about 92% transmission per window pass at 1500 nm, but the VIS window still has about 70% transmission per pass at 1500 nm. We do not have much experience with femtosecond pulsed lasers. Although I do not expect any thermal damage due to average power heating, depending on the peak power density and duration of the pulse, ablation of atomic layers of the µ-mirrors could be possible.

    Transmission information can be found in our application note:

    Wavelength Transmittance Considerations for DLP DMD Windows (Rev. C)

    Fizix

  • 0 in reply to Fizix
    Intellectual 425 points
    Hello Fizix,

    I was wondering if you can kindly guide me throughout each step you have followed when doing your calculations in order to obtain 5.7 nJ/cm2 and 300 nJ.

    Thanks a lot for your help, very appreciated.

    Pablo