Abstract: A polyimide precursor for producing a flexible electronic device substrate that provides a polyimide with reduced charge-up, particularly a polyimide in the form of a film. When a polyimide film having a thickness of 10 ?m is formed using the polyimide precursor, and a pair of electrodes is formed with a distance d on the polyimide film, and when the polyimide film is irradiated with a laser beam while applying a DC voltage with an electric field strength of 0.1 to 10 V/?m between the pair of electrodes; two SHG lights are observed between the pair of electrodes and satisfy a symmetry ratio of 0.5 or more. The symmetry ratio (LR ratio)=Ismall/Ilarge, wherein, Ilarge represents the peak intensity of the SHG light with the larger intensity, and Ismall represents the peak intensity of the SHG light with the smaller intensity.

Abstract: A detection apparatus having means for evaluating generation and disappearance of a carrier is provided. A detection apparatus detects, on the basis of high-order harmonics, an electric field distribution or a carrier distribution between electrodes arranged on an object to be observed.