Method and arrangement for short coherence holography

A method for short-coherence holography of an at least partially light-diffusing object:

• providing a holographic measuring arrangement comprising:
• at least one frequency comb light source (1a, 1b, 1c, 1.1, 1.2) of a short coherent or quasi short-coherent light with a comparatively small coherence length with respect to an object extension and with controllable frequency comb light by predetermined change of an optical path length L1 in its integrated cavity or in at least one cavity (1d) assigned to the at least one frequency comb light source,
• an unbalanced two-beam interferometer with a reference arm (R) and an object arm (O), which applies measuring light from the at least one frequency comb light source to an object, with a detection channel for measuring light that returns,
• at least one rasterized detector (6) for capturing holograms and with a computer or computer system for the highly dynamic control of the at least one frequency comb light source and synchronization of the hologram capture with respect to the at least one frequency comb light source and algorithms for numerical hologram reconstruction,
• means for at least approximately determining a distance and a velocity of the object to be measured and an interface for data transfer;
• generating a reference bundle of rays and an object bundle of rays using the unbalanced two-beam interferometer,
• in which a mean optical path difference Xm different from zero exists, and
• which, at its output, has a surface-like hologram detection area HDB, in which the at least one rasterized detector spectrally integrally detecting at least in spectral sub-ranges is arranged, and
• which in its surface-like hologram detection area HDB at a point DP of the HDB, for an optically detected object point OP, always has an optical object point-related path difference x_OP_DP different from zero,
• wherein in the unbalanced two-beam interferometer, short-coherent or quasi short-coherent light having frequency comb characteristic with the frequency interval Δf1=c/Y1 in the frequency space is used for hologram formation, wherein Y1 represents the delay length of the delay line in the frequency comb generation, and at least one short-coherence hologram is detected in the capturing process by the at least one rasterized detector,
• and in which the inequation
• |(x—OP—DP−n1·Y1)|<lc
• is satisfied for at least one integer n1 with n1=1, 2, 3, . . . , and for at least one optically detected, at least partially light-diffusing object point OP - and thus the at least one short-coherence hologram forms in at least one sub-range of the at least one rasterized detector - with lc as the coherence length of the short-coherent or quasi short-coherent comb light, which returns from the light-diffusing object point OP and contributes to hologram formation, and with x_OP_DP as the optical path difference at a point DP of the surface-like hologram detection area HDB for the optically detected, light-diffusing object point OP;
• performing at least one measurement for determining the distance and the velocity - or a multiple measurement of the distance, also by means of a conducted time measurement suitable for determination of the velocity of the object (51, 52) to be measured, which with at least one component of its movement also moves in the propagation direction of the measuring light,
• and the magnitude of the distance and the velocity is available as information in measurement real time at least approximately, and is provided for the measurement method for shape detection by means of optical sectioning,
• and in the holographic sampling process, the spatial pulse interval Y1 of the emitted short pulses of a pulse train of the frequency comb light source is changed by a predetermined change of the optical path length (L1) of at least one integrated cavity (1d) or a cavity (1d) assigned to the frequency comb light source which influences the short coherent or quasi short-coherent light in its frequency comb interval,
• on the basis of the information about the velocity and distance of the object (51,52), which is provided in real time, and
• the optical path length of this cavity (1d) is changed in form of a long scan—either increased or decreased,
• so that the ordinal number q of object-sampling short pulses is kept constant for at least the capturing time delta_t_Hol of the at least one short-coherence hologram,
• by making the first derivative over time of the spatial pulse interval, which results from the delay length of the frequency comb-forming cavity, at least approximately equal to a value of 2/q-times the component of the velocity of the object in the movement direction or the difference velocity between the at least one rasterized detector and the object, wherein the ordinal number q results from the quotient of optical path length 1_opt, from the position of optical path difference zero at the unbalanced two-beam interferometer in the object optical path to a sampled object point OP, and the spatial pulse interval Y1,
• so that the phase in the at least one short-coherence hologram changes by less than 2 Pi at least in a sub-range thereof;
• and
• capturing the at least one short-coherence hologram using the at least one rasterized detector and performing a numerical reconstruction thereof, whereby at least one sectional plane E or one sectional area is calculated and at least one intensity amplitude of a light-diffusing object point OP from the reconstructed hologram above a threshold value 1S is evaluated as a characteristic of the presence of a light-diffusing object point OP of the object space.