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In order to solve the problem that CCDs cannot measure the full spectral range in a single measurement, we propose a new wavelength-fitting algorithm that combines the polynomial algorithm applied to the fixed grating with grating equation without CCD or spectrum assembling. Both the grating rotating angle and pixel coordinate of the CCD are written in our wavelength-fitting function. With the calibration of the 576.96 and 579.07 nm mercury spectral line, we can determine that wavelength error of 576.96 nm is between 0.002 and 0.1 nm and wavelength error of 579.07 nm is between 0.006 and 0.06 nm. The calculation results show that the new algorithm can gain more precise wavelength accuracy without a complex assembling operation.

We investigated the optical property of periodic inverted pyramidal microcavities and observed large area field enhancement outside a cavity when the incident wavelength and structure parameters match certain relations. The mechanism of this phenomenon has been studied. Propagating surface plasmons and the standing wave effect both contribute to the field enhancement outside the cavity. The relations between the incident wavelength and structure parameters have been clarified. Based on the relations, one can control the field enhancement outside the cavity for a specific laser wavelength.