Abstract:
Interferometrische Meßsysteme sind bekannt. Sie enthalten eine Lichtquelle zur Erzeugung kohärenten Lichtes und einen Interferometeraufbau, bestehend aus mindestens einem Strahlteiler und zwei Reflektoren sowie Linsen zur Bündelung des Lichtstrahls. Erfindungsgemäß dient ein solches Meßsystem zur Untersuchung des von einer Laserlichtquelle (1) ausgesandten Lichtbündels (30) auf Frequenz, Moden, Modenstabilität, Modenverteilung sowie Kohärenzlänge und Kohärenzzeit etc. Das Lichtbündel (30) wird durch eine Linse parallel gemacht, gelangt anschließend über den Strahlteiler (3) in zwei Teilbündel (31, 32) zu den Reflektoren (4, 5). Einer der beiden Teilbündel durchläuft ein Referenz-Interferenzmuster (7). Beide Teilbündel (31, 32) interferieren miteinander und werden über ein optisches System zur Verringerung der numerischen Apertur einem Photoempfänger (10) zugeführt. Besonders vorteilhaft ist es, wenn möglichst viele optische Bauelemente, insbesondere die Linse (2) der Strahlteiler (3) die Reflektoren (4, 5) und das Referenz-Interferenzmuster (7) auf einem Block (6) monolithisch integriert sind.
Abstract:
The subject matter disclosed herein pertains to a method for screening drugs using second-harmonic generation microscopy. The tissue is scanned with a pulsed laser light which has an excitation wavelength. At least some of microtubules within the tissue produce generated light with a second-harmonic wavelength that is half the excitation wavelength. A microtubule pattern within the tissue is determined based on an analysis of the generated second-harmonic wavelength.
Abstract:
A method and apparatus for determining the quality of a multimode laser beam (10). In the preferred embodiment, the apparatus includes a lens (32) for creating a transformed or imaged waist from the input beam. The location of the transformed beam waist and its diameter are then determined. These steps can be carried out by chopping the beam using a rotating hub (14) having apertures (36,38) for selectively passing the beam. Preferably, one of the apertures has a pair of 45.degree. knife edges (40,42). The transmission of the beam past the knife edge is monitored by a detector (30). In operation, the lens focal position is varied while the transmission of the beam past the knife edge is monitored in order to locate and measure the diameter of the transformed waist. The diameter of the beam at one other known location is measured. A processor then calculates beam quality by fitting these measurements to a mathematical model. Once the quality of the beam is calculated, the location of the original beam waist and its diameter can be derived. Once all of the beam parameters are derived, the propagation characteristics of the beam can be predicted. In the preferred embodiment, the transformed beam waist is located by taking incremental measurements of beam diameter, at both the front and rear planes of the hub, as the lens is moved a distance at least a great as the diameter of the hub. The diameter measurements are spliced together by the processor to provide an axial profile of the beam over a distance twice as large as the diameter of hub. This data can then be analyzed to find the minimum which corresponds to the location of the transformed beam waist.
Abstract:
A photodetector produces an output signal in response to irradiation by an optical beam from a pulsed laser. A delay unit delays the output signal for a period corresponding to one-half of one cycle of a beat frequency generated by interaction of two frequency components in the optical beam corresponding to two predetermined longitudinal modes of operation of the laser. A differential mixer subtractively combines the output of the photodetector with the output of the delay unit, to produce an output signal having the main profile of the laser pulses suppressed, and the beat frequency component, if present, amplified. A resonant circuit and amplifier may be provided to further amplify the beat frequency component. The output of the amplifier is integrated to produce a DC signal having a magnitude which corresponds to the amplitude of the beat frequency component. The DC signal is compared with a threshold value to discriminate between single and multimode operation of the laser. An optical shutter may be closed in response to sensed multi-longitudinal mode operation to block the laser beam and protect equipment which would otherwise be damaged thereby.
Abstract:
A method and apparatus for performing a modal decomposition of a laser beam are disclosed. The method includes the steps of performing a measurement to determine the second moment beam size (w) and beam propagation factor (M2) of the laser beam, and inferring the scale factor (wO) of the optimal basis set of the laser beam from the second moment beam size and the beam propagation factor, from the relationship: wO=w/M2. An optimal decomposition is performing using the scale factor wO to obtain an optimal mode set of adapted size. The apparatus includes a spatial light modulator arranged for complex amplitude modulation of an incident laser beam, and imaging means arranged to direct the incident laser beam onto the spatial light modulator. Fourier transforming lens is arranged to receive a laser beam reflected from the spatial light modulator. A detector is placed a distance of one focal length away from the Fourier transforming lens for monitoring a diffraction pattern of the laser beam reflected from the spatial light modulator and passing through the Fourier transforming lens. The apparatus performs an optical Fourier transform on the laser beam reflected from the spatial light modulator and determines the phases of unknown modes of the laser beam, to perform a modal decomposition of the laser beam.
Abstract:
Technologies are generally described for techniques useful in an interferometer system. In some examples, a system may include a first waveguide effective to propagate a first wave in a first mode. In some examples, the system may include a second waveguide effective to, in response to the first wave, propagate second and third waves in second and third modes, respectively. In some examples, the second waveguide may be effective to reflect the second and third waves off a reflection surface to produce first, second, third and fourth reflected waves. In some examples, the second waveguide may be effective to propagate the first and third reflected waves in the second mode and propagate the second and fourth reflected waves in the third mode.
Abstract:
A technique for the simultaneous measurement, in real time, of the changes in mode size, pulse length, and power of a wavetrain of laser pulses delivered by mode-locked or other pulsed laser systems contemplates directing respective portions of the beam along each of three beam paths. The beam portions along the first and second beam paths are subjected to respective, and different, degrees of focusing, and then passed through respective non-linear elements which generate radiation at the second harmonic. The first harmonic components are removed, and the second harmonic components are passed to respective first and second detectors which generate signals representative of the total second harmonic energy along each of the first and second beam paths. The beam portion along the third beam path is passed to a detector which generates a signal representative of the total energy in the beam pulse. The three signals are combined to give values proportional to peak power, pulse length, and mode size.
Abstract:
A device for measuring an aberration has an image sensor, projection optics for optically projecting onto the image sensor, an optical unit for influencing the optical projection onto the image sensor so that the result on the image sensor is a multiple image of a plurality of sub-images, wherein the optical unit has at least one region per sub-image, wherein the regions influence different lateral portions of a wavefront incident on the projection optics in different ways, and an evaluator configured to determine information relating to the aberration based on the multiple image.