A method for a target image reconstruction is provided. The method includes emitting stepped frequency waveforms having different constant frequencies at different periods of time, modulating the stepped frequency waveforms into frequency ranges each having a first frequency and a second frequency, wherein each of the stepped frequency waveforms are increased from the first frequency to the second frequency based on a range function, wherein the modulated stepped frequency waveforms are arranged with some sparsity factor. The method further includes transmitting the modulated stepped frequency waveforms to a target and accepting reflection of the modulated stepped frequency waveforms reflected from the target interfering the modulated stepped frequency waveforms and the reflection of the modulated stepped frequency waveforms to produce beat signals of interferences between the modulated stepped frequency waveforms and the reflection of the modulated stepped frequency waveforms, and reconstructing an image of the target from the beat signals.

A method for a target image reconstruction is provided. The method includes emitting stepped frequency waveforms having different constant frequencies at different periods of time, modulating the stepped frequency waveforms into frequency ranges each having a first frequency and a second frequency, wherein each of the stepped frequency waveforms are increased from the first frequency to the second frequency based on a range function, wherein the modulated stepped frequency waveforms are arranged with some sparsity factor. The method further includes transmitting the modulated stepped frequency waveforms to a target and accepting reflection of the modulated stepped frequency waveforms reflected from the target interfering the modulated stepped frequency waveforms and the reflection of the modulated stepped frequency waveforms to produce beat signals of interferences between the modulated stepped frequency waveforms and the reflection of the modulated stepped frequency waveforms, and reconstructing an image of the target from the beat signals.

A method for measuring the surface topography of an object including the following steps: a) providing source radiation and dividing the source radiation into illumination radiation and reference radiation, b) illuminating the surface of the object with illumination radiation in a planar illumination field, the surface of the object being illuminated simultaneously with more than one spatial radiation mode and the radiation modes of the illumination being spatially and temporally coherent, but with a fixed phase difference from one another, and c) overlaying the reference radiation on illumination radiation back-scattered at the surface of the object, and detecting an interference signal of the overlaid radiation with a detector. Steps a) to c) are carried out for at least two different, fixed wavelengths. The surface topography of the object is determined by means of digital holography.

A method of air refractive index correction for an absolute long distance measurement adopting a two-color method based on a single wavelength and a synthetic wavelength is provided. Two lasers emit two laser beams with a constant single wavelength and a variable wavelength, respectively, to form a synthetic wavelength chain from large to small through a laser interferometric system. Each order of the synthetic wavelength chain is used to obtain a series of the estimate values of optical distance with gradually increasing accuracy. After optical distances corresponding to a minimum synthetic wavelength and a single wavelength are obtained simultaneously, the corrected absolute distance is achieved according to the principle of the two-color method for air refractive index correction. The method can realize full-path correction of air refractive index along the actual path of the distance measurement, and has low requirements on the measurement precision of environmental parameters such as temperature and pressure.

The application discloses an atom interferometer comprising an optical cavity and method of operation thereof. The atom interferometer includes a vacuum chamber, an optical cavity, a source for providing a cloud of atoms in the optical cavity in use, and one or more light sources. The one or more light sources are for generating, in the cavity, in use a first light beam having a first polarisation and at a first frequency for a two-photon interaction in the atoms; and a counterpropagating second light beam having a second polarisation orthogonal to the first polarisation and at a second frequency for the two-photon interaction in the atoms. The atom interferometer also includes an electro-optic element arranged in the cavity to be operable to simultaneously change; the resonant frequency of the cavity for light in the first polarisation to track changes in the frequency of the first light beam to compensate for the doppler shift of the falling atoms in use; and the resonant frequency of the cavity for light in the second polarisation to track changes in frequency of the counterpropagating second light beam to compensate for the doppler shift of the falling atoms in use.

An optoelectronic device for a self-mixing interferometer includes a driver block, a semiconductor laser (SCL), a detector (DTC) and a switching network (SWN). The driver block is operable to provide a time modulated control signal, wherein the control signal has a periodic waveform. The semiconductor laser (SCL) is operable to emit a laser light with a time-dependent characteristics being a function of the control signal and a self-mixing interference optical feedback. The detector (DTC) is operable to generate a detection signal depending on the time-dependent characteristics. The switching network (SWN) is arranged to provide a time sequence of detection signals per period of the control signal.

An absolute distance measurement apparatus and method using laser interferometric wavelength leverage includes a light source system, a wavelength-leverage laser interferometric system and an interference signal processing and controlling system. The light source system outputs a orthogonally linearly polarized beam with the wavelength .sub.1 and the wavelength .sub.2. The orthogonally linearly polarized beam projects onto the wavelength-leverage laser interferometric system to form the interference beam. The interference beam projects onto the interference signal processing and controlling system. In the wavelength-leverage laser interferometric system, the synthetic wavelength and the single wavelength as well as the measured absolute distance and the moving displacement of the cube-corner prism in the reference arm form a wavelength-leverage absolute distance measurement relationship.

An apparatus can be provided which can include a laser arrangement which can be configured to provide a laser radiation, and can include an optical cavity. The optical cavity can include a dispersive optical first arrangement which can be configured to receive and disperse at least one first electro-magnetic radiation so as to provide at least one second electro-magnetic radiation. Such cavity can also include an active optical modulator second arrangement which can be configured to receive and modulate the at least one second radiation so as to provide at least one third electro-magnetic radiation. The optical cavity can further include a dispersive optical third arrangement which can be configured to receive and disperse at least one third electro-magnetic radiation so as to provide at least one fourth electro-magnetic radiation. For example, actions by the first, second and third arrangements can cause a spectral filtering of the fourth electro-magnetic radiation(s) relative to the first electro-magnetic radiation(s). The laser radiation can be associated with the fourth radiation(s), and a wavelength of the laser radiation can be controlled by the spectral filtering caused by the actions by the first, second and third arrangements.

A tunable light source having a temporal coherence length such that interference fringes are detected within the optical path difference of the interferometer is spectrally controlled to produce multiple wavelengths during sequential fractions of the integration time of the detector of the interferometer. The wavelengths are selected so as to produce a visible correlogram at each integration time according to spectrally controlled interferometry (SCI) principles. Such different wavelengths may be produced by stepwise or continuous modulation. The modulation step is repeated sequentially while changing the period of modulation to produce a succession of predetermined spatial patterns of interference fringes, as required for interferometric measurements. The approach enables the practice of SCI with common-path apparatus used for conventional phase shifting, thereby combining the advantages of high-coherence and white-light interferometry. A suitable time-modulated source combines a coherent source with an optical modulator and a waveform generator synchronized with the source.

An apparatus can be provided which can include a laser arrangement which can be configured to provide a laser radiation, and can include an optical cavity. The optical cavity can include a dispersive optical first arrangement which can be configured to receive and disperse at least one first electro-magnetic radiation so as to provide at least one second electro-magnetic radiation. Such cavity can also include an active optical modulator second arrangement which can be configured to receive and modulate the at least one second radiation so as to provide at least one third electro-magnetic radiation. The optical cavity can further include a dispersive optical third arrangement which can be configured to receive and disperse at least one third electro-magnetic radiation so as to provide at least one fourth electro-magnetic radiation. For example, actions by the first, second and third arrangements can cause a spectral filtering of the fourth electro-magnetic radiation(s) relative to the first electro-magnetic radiation(s). The laser radiation can be associated with the fourth radiation(s), and a wavelength of the laser radiation can be controlled by the spectral filtering caused by the actions by the first, second and third arrangements.