To study the radiation emitted by the human skin, the emissivity of its surface must be known. We present a new approach to measure the emissivity of the human skin in vivo. Our method is based on the calculation of the difference of two infrared images: one acquired before projecting a CO(2) laser beam on the surface of the skin and the other after such projection. The difference image contains the radiation reflected by the skin, which is used to calculate the emissivity, making use of Kirchhoff's law and the Helmholtz reciprocity relation. With our method, noncontact measurements are achieved, and the determination of the skin temperature is not needed, which has been an inconvenience for other methods. We show that it is possible to make determinations of the emissivity at specific wavelengths. Last, our results confirm that the human skin obeys Lambert's law of diffuse reflection and that it behaves almost like a blackbody at a wavelength of 10.6 microm.

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Mid-infrared optical microelements, like lenses or array of them, can be used to couple light or to form images. We present simple methods to fabricate mid-infrared microlenses and other optical elements by means of irradiation of a polymer substrate with CO2 laser or by the melting method. Application of these methods can lead to a mass production, low cost midinfrared elements. It is analyzed the influence of some fabrication process variables in the fmal parameters of the elements. The quality of the microlenses was characterized by direct measurement of their surface profile through mechanical (surface analyzer) and optical (interference) methods. Capability ofmicroelements to form infrared images is shown.