Recycling optical cavity, optical system, and optical construction

An optical system for sensing a test material, the optical system comprising:

• a recycling optical cavity comprising at least first and second optically reflective walls, at least a portion of each of the first and second optically reflective walls comprising a plurality of microlayers numbering at least 10 in total, each of the microlayers having an average thickness of less than about 500 nm;
• and
• a test material disposed in the recycling optical cavity and configured to emit at least a second light having a second wavelength L2 when irradiated with a first light having a different first wavelength L1,
• such that for at least one of s- and p-polarized incident lights incident in an incident plane at a same first incident angle, an optical transmittance of the plurality of microlayers versus wavelength:
• for the first optically reflective wall, comprises a first band edge along which the transmittance generally decreases with increasing wavelength, the first band edge having a midpoint at a wavelength La;
• and
• for the second optically reflective wall, comprises second and third band edges with the transmittance generally decreasing with increasing wavelength along the second band edge and generally increasing with increasing wavelength along the third band edge, the second and third band edges having midpoints at respective wavelengths Lb and Lc, wherein L1<La<Lb<Lc.

An optical system comprising:

• at least one light source configured to emit a light having at least a first wavelength;
• a recycling optical cavity configured to receive the emitted light from the at least one light source and comprising at least first and second optically reflective walls, at least a portion of each of the first and second optically reflective walls comprising a plurality of microlayers numbering at least 10 in total, each of the microlayers having an average thickness of less than about 500 nm;
• and
• at least one optical detector configured to receive and detect light exiting the recycling optical cavity and having at least the first wavelength and a different second wavelength;
• such that for at least one of s- and p-polarized incident lights incident in an incident plane, optical transmittances of the first and second optically reflective walls versus wavelength comprise first, second and third transmittance bands having corresponding and nonoverlapping full width at half maxima FWHM1, FWHM2, and FWHM3, wherein:
• at a first incident angle, only FWHM1 comprises the first wavelength and none of the three FWHMs comprises the second wavelength;
• at a second incident angle different than the first incident angle, only FWHM2 comprises the first wavelength and none of the three FWHMs comprises the second wavelength;
• and
• at a third incident angle different than the first and second incident angles, only FWHM3 comprises the second wavelength and none of the three FWHMs comprises the first wavelength.