Method and apparatus for processing a minute portion of a specimen

An apparatus for detecting a photoacoustic signal comprising:

• a light source;
• modulation means for modulating the intensity of light from said light source at a predetermined modulation frequency;
• exciting means for exciting a specimen by directing said intensity-modulated light onto the specimen, thereby generating a photoacoustic effect in the specimen;
• detection means for detecting the photoacoustic effect generated in the specimen and producing a detection signal indicative of the detected photoacoustic effect;
• and
• information extracting means for extracting information about the surface and interior of the specimen from the detection signal produced by said detection means;
• wherein said exciting means includes a near-field optical scanning microscope, and wherein the intensity-modulated light is emitted from an aperture of the near-field optical scanning microscope while a distance between the aperture of the near-field optical scanning microscope and the surface of the specimen is maintained constant irrespective of the photoacoustic effect generated in the specimen.