A method and apparatus for precision laser scanning suitable for precision machining or cleaning using an ultrashort pulsed laser beam are disclosed. The apparatus employs a laser source that emits a pulsed laser beam, a dispersion compensation scanner that scans the pulsed laser beam, and a focusing unit that focuses the pulsed laser beam from the dispersion compensation scanner on a work piece. The dispersion compensation scanner comprises a first scanning device that scans the pulsed laser beam in a first direction and that causes dispersion of the pulsed laser beam. The dispersion compensation scanner further comprises a first dispersion compensation device that compensates for the dispersion caused by the first scanning device. Effects of polarization of the ultrashort pulsed laser beam on the quality of machining are described. Uses of the invention in direct fabrication of photolithographic masks and in work piece cleaning are also described.

Ultrashort pulsed laser micromachining/submicromachining using an acoustooptic scanning device with dispersion compensation

An optical scanning device for scanning an optical record carrier. The optical scanning device includes: a radiation source system (661; 761); an optical element (1; 101; 201; 301) comprising a first fluid (A) and a second fluid (B; C) separated from each other by a fluid meniscus (16; 116, 138; 216; 316) having an adjustable configuration; and a control system (20; 120; 220; 320) arranged to adjust the fluid meniscus configuration to introduce a first type of wavefront modification. The first type of wavefront modification causes the radiation beam to be redirected from an input radiation beam path (2; 102; 244; 348) onto one of a plurality of output radiation beam paths (24, 26; 140; 246; 350) which each have a different angular displacement (α, β, Ϝ, δ, e) from the input radiation beam path. The control system is further arranged to adjust the fluid meniscus configuration to introduce a second type of wavefront modification. The second type of wavefront modification is arranged to compensate a wavefront aberration of the radiation beam, the compensated wavefront aberration being adjusted in accordance with the angular displacement.

Optical Scanning Device

A technique and apparatus is disclosed for micro machining using an ultra short laser pulse in the range of femto second pulsing. The system is also applicable for smaller or higher pulse rates depending upon the application. The system includes methods for improving the beam quality of the laser beam by filtering. Moreover, it includes the concept of scanning the laser beam using acousto optic deflectors in the X-Y direction rather than conventional mechanical movement of the work piece or deflecting the beam using a mirror. The technique also incorporates means for modulating the ultra short laser pulse in order to control the number of pulses of the ultra short laser pulse which will strike the target surface at each of the target points by a combination of acousto optic modulators. The concept of applying elliptical or circular laser beam spots for machining rather than a circular one is also disclosed.

Three dimensional micro machining with a modulated ultra-short laser pulse

We present a novel concept for Fourier synthesis of optical pulses using Brillouin selective sideband amplification in optical fibers and demonstrate the generation of a 7.8 GHz pulse train using two CW lasers and two phase modulators.

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Optical pulse synthesis using Brillouin selective sideband amplification

An apparatus which attenuates a light signal polarized in a first direction. The apparatus includes a polarization rotation unit and an output unit. The polarization rotation unit rotates the polarization of the light signal to produce a polarization rotated light signal having a polarization component in the first direction and a polarization component in a second direction which is substantially 90 degrees with respect to the first direction. The output unit passes, as an output signal, the polarization component in the second direction of the polarization rotated light signal and blocks the polarization component in the first direction. The polarization rotation unit includes an electromagnet and a permanent magnet which apply magnetic fields in specific directions with respect to the light path. Various yoke constructions are provided for the electromagnet and the permanent magnet. A control circuit maintains the output power of the output signal at a constant level, or maintains a constant ratio between the power level of the output signal and the power level of he light signal before the polarization is rotated. The apparatus can have a wavelength dependent attenuation which compensates for the wavelength dependent gain of an optical amplifier.

Variable optical attenuator which applies a magnetic field to a Faraday element to rotate the polarization of a light signal

A solid-state laser architecture producing a beam of extremely high quality and brightness, including a master oscillator (10) operating in conjunction with a zig-zag amplifier (16,30), an image relaying telescope (17) and a phase conjugation cell (20). One embodiment of the laser architecture compensates for birefringence that is thermally induced in the amplifier (16), but injects linearly polarized light into the phase conjugation cell (20). Another embodiment (19) injects circularly polarized light into the phase conjugation cell (20) and includes optical components that eliminate birefringence effects arising in a first pass through the amplifier (16,30). Optional features (26) permit the use of a frequency doubler assembly to provide output at twice optical frequencies, and an electro-optical switch or Faraday rotator (71) to effect polarization angle rotation if the amplifier material (16,30) can only be operated at one polarization. The zig-zag amplifier (16,30) is cooled by flow of cooling liquid, preferably using longitudinal flow to minimize temperature gradients in a vertical direction, and has cooling channel seals (50,52) disposed in dead zones that receive no light, to minimize optical damage to the seals (50,52). Light is input to the amplifier (16) at a near normal angle of incidence, to minimize polarization by reflection and to permit a polarizer (14) to be used to extract an output beam from the amplifier (16,30). Antireflective coatings (60) on edges and on sides of the amplifier (16,30) eliminate parasitic oscillations, and wedge-shaped windows (36) provide uniform pumping by eliminating gaps between diode arrays (32).

High brightness solid-state laser with zig-zag amplifier

A solid-state laser architecture producing a beam of extremely high quality and brightness, including a master oscillator operating in conjunction with a zig-zag amplifier, an image relaying telescope and a phase conjugation cell. One embodiment of the laser architecture compensates for birefringence that is thermally induced in the amplifier, but injects linearly polarized light into the phase conjugation cell. Another embodiment injects circularly polarized light into the phase conjugation cell and includes optical components that eliminate birefringence effects arising in a first pass through the amplifier. Optional features permit the use of a frequency doubler assembly to provide output at twice optical frequencies, and an electro-optical switch or Faraday rotator to effect polarization angle rotation if the amplifier material can only be operated at one polarization. The zig-zag amplifier is cooled by flow of cooling liquid, preferably using longitudinal flow to minimize temperature gradients in a vertical direction, and has cooling channel seals disposed in dead zones that receive no light, to minimize optical damage to the seals. Light is input to the amplifier at a near normal angle of incidence, to minimize polarization by reflection and to permit a polarizer to be used to extract an output beam from the amplifier. Antireflective coatings on edges and on sides of the amplifier eliminate parasitic oscillations, and wedge-shaped windows provide uniform pumping by eliminating gaps between diode arrays.

Solid-state zig-zag slab optical amplifier

Apparatus, and a related method, for compensating for birefringence introduced in a birefringent medium, such as a solid-state amplifier. The invention includes the combination of a quarter-wave plate, a Faraday rotator and a mirror, which may be a phase conjugation cell. Light passing through the quarter-wave plate is substantially circularly polarized, which is advantageous if the mirror is a phase conjugation cell using stimulated Brillouin scattering (SBS). A second pass through the quarter-wave plate provides a linearly polarized beam of which the polarization angle is orthogonally related to that of the original beam, to facilitate out-coupling of energy from the apparatus. The Faraday rotator effects a total polarization angle rotation of 90° in two passes and helps compensate for birefringence when the beam is passed through the birefringent medium again on the return pass. The combination of the quarter-wave plate and the Faraday rotator provides better birefringence cancellation than either element acting alone.

Birefringence compensated laser architecture

Apparatus and a related method for generating a second harmonic frequency optical output from a fundamental frequency input beam, without significant birefringence. The apparatus includes two Type II doubler crystals of equal length arranged with their corresponding axes parallel to each other, and a polarization rotator positioned between the doubler crystals, to rotate the polarization angle of a residual fundamental frequency component of an output beam from one of the crystals by 90° or an odd multiple of 90°. Random birefringence introduced into one of the doubler crystals is virtually canceled in the other, and the assembly of the two crystals and the polarization rotator may be angularly adjusted as needed for phase matching or tuning, without detracting from the birefringence compensation capability. The invention is also disclosed in the context of a phase conjugated master oscillator power amplifier (PC MOPA) system.

Birefrigence-compensated alignment-insensitive frequency doubler

A system and method for monitoring the mode of an input beam to a phase conjugated master oscillator power amplifier (PC MOPA). In order to prevent catastrophic optical damage to the MOPA components, the method and system shuts down the master oscillator when a multi-mode input beam is detected.

Pierre Randall J St

Papers

High brightness solid-state laser with zig-zag amplifier

Solid-state zig-zag slab optical amplifier

Birefringence compensated laser architecture

Birefrigence-compensated alignment-insensitive frequency doubler

Phase conjugated master oscillator-power amplifier breakdown control