Abstract: An optical stack for sensing a presence of an analyte is provided. The optical stack includes a sensor material. The sensor material includes a first optical response including a first optical property having a second value in response to an excitation signal including the first optical property having a first value different from the second value. The first optical response includes a second optical property sensitive to the presence of the analyte. The optical stack includes a first optical film disposed proximate the sensor material and includes a third optical property having respective third and fourth values in response to the respective first and second values of the first optical property. The third value is different from the fourth value by at least a factor of 2.

Abstract: A measurement system is disclosed and includes a light source, a receiver, a measurement subject, and a reflector. The reflector is disposed on an opposite side of the measurement subject than are the light source and the receiver.

Abstract: A recycling optical cavity is defined at least by first and second optical films and is configured to receive a test material therein. The test material is configured to emit at least a second light having a second wavelength when irradiated with a first light having a first wavelength. For at least one of s- and p-polarized incident lights incident in an incident plane, and at the first and second wavelengths: at a first incident angle, the first optical film has respective optical transmittances T11(?1) and T12(?1), and the second optical film has respective optical transmittances T21(?1) and T22(?1), wherein T11(?1)>T12(?1), T21(?1), T22(?1); and at a second incident angle, the first optical film has respective optical transmittances T11(?2) and T12(?2), and the second optical film has respective optical transmittances T21(?2) and T22(?2), wherein T21(?2)>T11(?2), T12(?2), T22(?2).