Method for photocopying a sequence of cut surfaces inside a light-scattering object with improved scanning
The invention relates to a free-beam interferometric method for illuminating a sequence of sectional areas in the interior of the light-scattering object. The method makes it possible for the user to select a larger image field and/or a higher image resolution than previously possible with the occurrence of self-interference of the specimen light from a scattering specimen.
1. A method for illuminating a sequence of sectional areas in the interior of a light-scattering object, the method comprising:
provision of a light source, which emits light with a predetermined central wavelength λ 0 and a coherence length less than 25 microns;
splitting the light of the light source into specimen light and reference light;
illumination of the object over the surface with the specimen light;
imaging of the specimen light scattered by the object with numerical aperture NA and magnification factor M onto an electronic camera with pixels with a pitch P along at least one axis in the camera plane;
causing interference of reference light and specimen light on the camera by establishing a path length profile and a phase gradient of the reference light along the predetermined axis in the camera plane;
displacement of the path length profile of the reference light at a time-dependent rate; and
detection of further camera images in each case at least indexed with a dimension for the time-dependent displacement of the path length profile, wherein the condition
2
3
+
2
λ
0
<
2
NA
*
P
M
≤
2
1
+
2
λ
0
is met.
2. The method according to claim 1 , wherein the phase gradient along the predetermined axis in the camera plane is established on half the Nyquist frequency.
3. The method according to any one of the preceding claims, wherein a surrounding interval of the indexing is predetermined for each indexed camera image of at least a partial number of the detected camera images and a weighted stack mean value of all the camera images of the surrounding interval is calculated and the calculated stack mean value of the indexed camera image is deducted to calculate the structurally improved camera image.
4. The method according to claim 3 , further comprising calculation of the images of the sectional areas in the interior of the object by two-dimensional Fourier filtering of the structurally improved camera images.
5. The method according to claim 1 , wherein the light-scattering object is the retina of a living eye.
6. The method according to claim 5 , further comprising biometric verification of the identity of a user.