Modal decomposition of light has been known for a long time, applied mostly to pattern recognition. With the commercialization of liquid-crystal devices, digital holography as an enabling tool has become accessible to all, and with it all-digital tools for the decomposition of light have finally come of age. We review recent advances in unravelling the properties of light, from the modal structure of laser beams to decoding the information stored in orbital angular momentum (OAM)-carrying fields. We show application of these tools to fiber lasers, solid-state lasers, and structured light created in the laboratory by holographic laser beam shaping. We show by experimental implementation how digital holograms may be used to infer the intensity, phase, wavefront, Poynting vector, polarization, and OAM density of some unknown optical field. In particular, we outline how virtually all the previous ISO-standard beam diagnostic techniques may be readily replaced with all-digital equivalents, thus paving the way for unravelling of light in real time. Such tools are highly relevant to the in situ analysis of laser systems, to mode division multiplexing as an emerging tool in optical communication, and for quantum information processing with entangled photons.

Creation and detection of optical modes with spatial light modulators

Methods for ultrashort pulse laser processing of optically transparent materials. A method for scribing transparent materials uses ultrashort laser pulses to create multiple scribe features with a single pass of the laser beam across the material, with at least one of the scribe features being formed below the surface of the material. This enables clean breaking of transparent materials at a higher speed than conventional techniques. Slightly modifying the ultrashort pulse laser processing conditions produces sub-surface marks. When properly arranged, these marks are clearly visible with side-illumination and not clearly visible without side-illumination. In addition, a method for welding transparent materials uses ultrashort laser pulses to create a bond through localized heating. The ultrashort pulse duration causes nonlinear absorption of the laser radiation, and the high repetition rate of the laser causes pulse-to-pulse accumulation of heat within the materials. The laser is focused near the interface of the materials, generating a high energy fluence at the region to be welded. This minimizes damage to the rest of the material and enables fine weld lines.

Transparent material processing with an ultrashort pulse laser

The invention relates to a projection system, comprising a radiation source, an illumination system operable to illuminate a structured mask, and a projection objective for projecting an image of the mask structure onto a light-sensitive substrate, wherein said projection system comprises an optical system comprising an optical axis or a preferred direction given by the direction of a light beam propagating through the optical system; the optical system comprising a temperature compensated polarization-modulating optical element described by coordinates of a coordinate system, wherein one preferred coordinate of the coordinate system is parallel to the optical axis or parallel to said preferred direction; said temperature compensated polarization-modulating optical element comprising a first and a second polarization-modulating optical element, the first and/or the second polarization-modulating optical element comprising solid and/or liquid optically active material and a profile of effective optical thickness, wherein the effective optical thickness varies at least as a function of one coordinate different from the preferred coordinate of the coordinate system, in addition or alternative the first and/or the second polarization-modulating optical element comprises solid and/or liquid optically active material, wherein the effective optical thickness is constant as a function of at least one coordinate different from the preferred coordinate of the coordinate system; wherein the first polarization-modulating optical element comprises optically active material with a specific rotation of opposite sign compared to the optically active material of the second polarization-modulating optical element.

Polarization-modulating optical element

A laser light beam is processed in a first optical path to produce light indications in a plurality of free spectral paths. These light indications are introduced through slits to produce signals at spaced positions at the opposite peripheries of a linear detector array. The distances between correlated pairs of energized detectors at the opposite peripheries of the array indicate the relative value of the laser wavelength in the free spectral ranges. The laser light beam is also processed in a second optical path, simultaneously with the processing of the laser light beam in the first optical path, to produce light in a single path. The second optical path is dependent upon the wavelength of the laser light beam. The light produced in the second optical path may be introduced through another slit to energize centrally disposed detectors in the array. The particular detectors energized are dependent upon the wavelength of the laser light. The detectors in the linear array may be scanned to produce signals related in time to the disposition of the detectors energized in the array. A data processing system processes these signals and produces a signal to adjust the wavelength of the laser beam to a particular value. When the laser is pulsed, the system described above may operate in real time after each pulse to adjust the laser before the next pulse to produce light at the particular wavelength.

System for, and method of, regulating the wavelength of a light beam

The Gaussian beam is the simplest case of laser beams actually appearing in practical optical systems. There also exist some other derived parameters, such as the Rayleigh range, which explains the extension of the beam waist along the propagation axis, and the Gouy phase shift, which describes how the phase includes an extra p-phase shift after crossing the beam waist region. Although simple, Gaussian beams exhibit a great variety of realizations when three-dimensional beams are studied. To properly evaluate such effects, certain other parameters have been defined by accounting for the ellipticity of the irradiance pattern, the longitudinal astigmatism, and the twisting of the irradiance profile. Gaussian laser beams are a reference of quality for a laser source. The description of other types of generalized, non-Gaussian, nonspherical, and nonorthogonal, laser beams is referred to the same type of parameters describing the Gaussian case.

Laser and Gaussian Beam Propagation and Transformation

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 (34) having apertures (36,38) for selectively passing the beam. Preferably, one of the apertures has a pair of 45° 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.

Apparatus for measuring the mode quality of a laser beam

A scannable dye laser is provided with an integral wavemeter under computer control. The wavemeter has improved fine and coarse readout components. Incremental laser scans are precisely linked together to provide long, continuous frequency scans. The fine readout of the wavemeter provides a means for accurately piecing together the incremental scans.

Scannable laser with integral wavemeter

Method and apparatus are disclosed in a frequency controlled tunable laser system which may be tuned selectively by an operator to any predetermined output radiation frequency within its operating range and servo-locked to maintain that output frequency, for rapidly and automatically maintaining and reacquiring a predetermined output radiation frequency despite momentary interruptions or perturbations of laser oscillation.

Method and apparatus for automatically reacquiring a predetermined output radiation frequency in a tunable laser system despite momentary perturbations of laser oscillation

A laser 10 is disclosed in which there are incorporated one or more diffractive optical elements (DOE's) 20. The DOE's can be used in place of conventional optics to save costs and allow design of resonators not heretofore possible. The ability to vary the reflectivity of the surface of a DOE in any desired pattern allows unprecedented control of both the intracavity mode as well as the mode of the output beam.

Laser resonators employing diffractive optical elements

An adjustable etalon mode selector is mounted within the optical cavity of a laser and includes a pair of spaced prisms mounted along the optical axis of the cavity with the laser beam passing therethrough and means for selectively adjusting the spacing between the prisms in a manner such that the resonant frequency of the laser cavity and etalon combination remains constant during the adjustment of the prism spacing in order that a particular mode of the operating wavelength spectrum of the laser may be selected for output, without the adjustment modulating the cavity natural resonant frequency.

Thomas F. Johnston

Papers

Apparatus for measuring the mode quality of a laser beam

Scannable laser with integral wavemeter

Method and apparatus for automatically reacquiring a predetermined output radiation frequency in a tunable laser system despite momentary perturbations of laser oscillation

Laser resonators employing diffractive optical elements

Adjustable etalon laser mode selector and method of adjustment