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Low solar background, high sensitivity active atomic resonance filter for underwater laser communications

  • US 4,829,597 A
  • Filed: 09/29/1986
  • Issued: 05/09/1989
  • Est. Priority Date: 09/29/1986
  • Status: Expired due to Fees
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First Claim
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1. A method for communicating through seawater at a wavelength λ

  • 1 comprising of steps of;

    a. transmitting light at a wavelength λ

    1 centered at a Fraunhofer line in the blue-green portion of the spectrum;

    b. providing a first optical filter having an optical transmission wavelength greater than a first cutoff wavelength λ

    c1, where λ

    1 >

    λ

    c1 ;

    c. providing a second optical filter spaced apart from the first optical filter and having an optical transmission wavelength less than a second cutoff wavelength λ

    c2, where λ

    c2 <

    λ

    c1 ;

    d. providing magnesium vapor positioned between and adjacent to the first and second optical filters;

    e. providing a buffer gas positioned between and adjacent to the first and second optical filters wherein the buffer gas is a noble gas;

    f. pumping the atomic vapor to a first excited state from which light can be absorbed at a narrowband wavelength centered at a Fraunhofer line λ

    1, wherein λ

    1 is 516.733 nm, 517.270 nm or 518.362 nm, thereby raising the atomic vapor to a second excited state;

    g. pumping the atomic vapor to a third excited state, whereby collisions with the buffer gas raise the atomic vapor to a fourth excited state, the atomic vapor at the fourth excited state exhibiting a fluorescence transition to the second excited state by emission of light at a fluorescence wavelength λ

    2, where λ

    2 <

    λ

    c2 and where λ

    2 is in the near UV portion of the spectrum and whereby light at the absorption wavelength λ

    1 incident on the first optical filter is transformed to light at the fluorescence wavelength λ

    2 and emitted through the second optical filter;

    h. detecting light at the fluorescence wavelength λ

    2 emitted through the second optical filter.

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