Abstract: A method for extending and enhancing bright coherent high-order harmonic generation into the VUV-EUV-X-ray regions of the spectrum involves a way of accomplishing phase matching or effective phase matching of extreme upconversion of laser light at high conversion efficiency, approaching 10?3 in some spectral regions, and at significantly higher photon energies in a waveguide geometry, in a self-guiding geometry, a gas cell, or a loosely focusing geometry, containing nonlinear medium. The extension and enhancement of the coherent VUV, EUV, X-ray emission to high photon energies relies on using VUV-UV-VIS lasers of shorter wavelength. This leads to enhancement of macroscopic phase matching parameters due to stronger contribution of linear and nonlinear dispersion of both atoms and ions, combined with a strong microscopic single-atom yield.

Abstract: Apparatus and methods for coherent diffractive imaging with arbitrary angle of illumination incidence utilize a method of fast remapping of a detected diffraction intensity pattern from a detector pixel array (initial grid) to a uniform spatial frequency grid (final grid) chosen to allow for FFT on the remapped pattern. This is accomplished by remapping the initial grid to an intermediate grid chosen to result in a final grid that is linear in spatial frequency. The initial grid is remapped (generally by interpolation) to the intermediate grid that is calculated to correspond to the final grid. In general, the initial grid (x,y) is uniform in space, the intermediate grid ({tilde over (x)},{tilde over (y)}) is non-uniform in spatial frequency, and the final grid ({tilde over (f)}x,{tilde over (f)}y) is uniform in spatial frequency.

Abstract: A method for extending and enhancing bright coherent high-order harmonic generation into the VUV-EUV-X-ray regions of the spectrum involves a way of accomplishing phase matching or effective phase matching of extreme upconversion of laser light at high conversion efficiency, approaching 10?3 in some spectral regions, and at significantly higher photon energies in a waveguide geometry, in a self-guiding geometry, a gas cell, or a loosely focusing geometry, containing nonlinear medium. The extension and enhancement of the coherent VUV, EUV, X-ray emission to high photon energies relies on using VUV-UV-VIS lasers of shorter wavelength. This leads to enhancement of macroscopic phase matching parameters due to stronger contribution of linear and nonlinear dispersion of both atoms and ions, combined with a strong microscopic single-atom yield.

Abstract: Phase-matched high-order harmonic generation of soft and hard X-rays is accomplished using infrared driving lasers in a high-pressure non-linear medium. The pressure of the non-linear medium is increased to multi-atmospheres and a mid-IR (or higher) laser device provides the driving pulse. Based on this scaling, also a general method for global optimization of the flux of phase-matched high-order harmonic generation at a desired wavelength is designed.

Abstract: Apparatus and methods for self-cleaning of optical elements in sealed environments over a wide range of operating optical frequencies prevent long-term power degradation by introducing low-pressure backfill of a reactive gas such as oxygen into a vacuum chamber containing the optical elements. The backfill pressure is preferably between 10?4 torr and 10 torr, and generally between 0.1 torr and 2 torr at room temperature. The vacuum chamber may be continuously evacuated and backfilled, or may be sealed after evacuation and backfill is performed.

Abstract: Phase-matched high-order harmonic generation of soft and hard X-rays is accomplished using infrared driving lasers in a high-pressure non-linear medium. The pressure of the non-linear medium is increased to multi-atmospheres and a mid-IR (or higher) laser device provides the driving pulse. Based on this scaling, also a general method for global optimization of the flux of phase-matched high-order harmonic generation at a desired wavelength is designed.

Abstract: All-optical quasi-phase matching (QPM) uses a train of counterpropagating pulses to enhance high-order harmonic generation (HHG) in a hollow waveguide. A pump pulse enters one end of the waveguide, and causes HHG in the waveguide. The counterpropagation pulses enter the other end of the waveguide and interact with the pump pulses to cause QPM within the waveguide, enhancing the HHG.

Abstract: A pre-ionized medium created by a capillary discharge results in more efficient use of laser energy in high-order harmonic generation (HHG) from ions. It extends the cutoff photon energy, and reduces the distortion of the laser pulse as it propagates down the waveguide. The observed enhancements result from a combination of reduced ionization energy loss and reduced ionization-induced defocusing of the driving laser as well as waveguiding of the driving laser pulse. The discharge plasma also provides a means to spectrally tune the harmonics by tailoring the initial level of ionization of the medium.

Abstract: Phase matching high harmonic generation (HHG) uses a single, long duration non-collinear modulating pulse intersecting the driving pulse. A femtosecond driving pulse is focused into an HHG medium (such as a noble gas) to cause high-harmonic generation (HHG), for example in the X-ray region of the spectrum, via electrons separating from and recombining with gas atoms. A non-collinear pulse intersects the driving pulse within the gas, and modulates the field seen by the electrons while separated from their atoms. The modulating pulse is low power and long duration, and its frequency and amplitude is chosen to improve HHG phase matching by increasing the areas of constructive interference between the driving pulse and the HHG, relative to the areas of destructive interference.

Abstract: Phase matching high harmonic generation (HHG) uses a single, long duration non-collinear modulating pulse intersecting the driving pulse. A femtosecond driving pulse is focused into an HHG medium (such as a noble gas) to cause high-harmonic generation (HHG), for example in the X-ray region of the spectrum, via electrons separating from and recombining with gas atoms. A non-collinear pulse intersects the driving pulse within the gas, and modulates the field seen by the electrons while separated from their atoms. The modulating pulse is low power and long duration, and its frequency and amplitude is chosen to improve HHG phase matching by increasing the areas of constructive interference between the driving pulse and the HHG, relative to the areas of destructive interference.

Abstract: All-optical quasi-phase matching (QPM) uses a train of counterpropagating pulses to enhance high-order harmonic generation (HHG) in a hollow waveguide. A pump pulse enters one end of the waveguide, and causes HHG in the waveguide. The counterpropagation pulses enter the other end of the waveguide and interact with the pump pulses to cause QPM within the waveguide, enhancing the HHG.

Abstract: A method for optimizing multipass laser amplifier output utilizes a spectral filter in early passes but not in later passes. The pulses shift position slightly for each pass through the amplifier, and the filter is placed such that early passes intersect the filter while later passes bypass it. The filter position may be adjust offline in order to adjust the number of passes in each category. The filter may be optimized for use in a cryogenic amplifier.

Abstract: An ultrashort pulse amplifier produces high-power ultrafast laser pulses. Pulses first have net negative (i.e. blue to red) chirp applied, and are then amplified in a laser amplifier. After amplification, the pulses are compressed using propagation through a block of material or other convenient optical system with a positive sign of chromatic dispersion. High-order dispersion correction may also be included.

Abstract: Accurate and efficient synchronization of two pulsed radiation sources (e.g. iwo mode locked lasers) is accomplished in stages. Rough synchronization is accomplished by synchronizing (for example) the fundamental repetition rate of the two lasers. Fine synchronization is accomplished by synchronizing high harmonics of the two lasers. More accurate synchronization may be accomplished by adding more stages, by utilizing light out of a nonlinear laser in which the two beams are crossed, or by utilizing heterodyne beats of the two laser beams. A dc offset signal may added to the control signal generated by the synchronization stages.

Abstract: A laser amplifier system amplifies pulses in a single “stage” from ˜10−9 joules to more than 10−3 joules, with average power of 1-10 watts, and beam quality M2<2. The laser medium is cooled substantially below room temperature, as a means to improve the optical and thermal characteristics of the medium. This is done with the medium inside a sealed, evacuated or purged cell to avoid moisture or other materials condensing on the surface. A “seed” pulse from a separate laser is passed through the laser medium, one or more times, in any of a variety of configurations including single-pass, multiple-pass, and regenerative amplifier configurations.

Abstract: An ultrashort pulse amplifier produces high-power ultrafast laser pulses. Pulses first have net negative (i.e. blue to red) chirp applied, and are then amplified in a laser amplifier. After amplification, the pulses are compressed using propagation through a block of material or other convenient optical system with a positive sign of chromatic dispersion. High-order dispersion correction may also be included.

Abstract: Accurate and efficient synchronization of two pulsed radiation sources (e.g. iwo mode locked lasers) is accomplished in stages. Rough synchronization is accomplished by synchronizing (for example) the fundamental repetition rate of the two lasers. Fine synchronization is accomplished by synchronizing high harmonics of the two lasers. More accurate synchronization may be accomplished by adding more stages, by utilizing light out of a nonlinear laser in which the two beams are crossed, or by utilizing heterodyne beats of the two laser beams. A dc offset signal may added to the control signal generated by the synchronization stages.

Abstract: A laser amplifier system amplifies pulses in a single “stage” from ˜10−9 joules to more than 10−3 joules, with average power of 1-10 watts, and beam quality M2<2. The laser medium is cooled substantially below room temperature, as a means to improve the optical and thermal characteristics of the medium. This is done with the medium inside a sealed, evacuated or purged cell to avoid moisture or other materials condensing on the surface. A “seed” pulse from a separate laser is passed through the laser medium, one or more times, in any of a variety of configurations including single-pass, multiple-pass, and regenerative amplifier configurations.

Abstract: Methods and apparatus are disclosed for the nonlinear generation of sum and difference frequencies of electromagnetic radiation propagating in a nonlinear material. A waveguide having a waveguide cavity contains the nonlinear material. Phase matching of the nonlinear generation is obtained by adjusting a waveguide propagation constant, the refractive index of the nonlinear material, or the waveguide mode in which the radiation propagates. Phase matching can be achieved even in isotropic nonlinear materials. A short-wavelength radiation source uses phase-matched nonlinear generation in a waveguide to produce high harmonics of a pulsed laser.

Abstract: Laser amplifiers and methods for amplifying a laser beam are disclosed. A representative embodiment of the amplifier comprises first and second curved mirrors, a gain medium, a third mirror, and a mask. The gain medium is situated between the first and second curved mirrors at the focal point of each curved mirror. The first curved mirror directs and focuses a laser beam to pass through the gain medium to the second curved mirror which reflects and recollimates the laser beam. The gain medium amplifies and shapes the laser beam as the laser beam passes therethough. The third mirror reflects the laser beam, reflected from the second curved mirror, so that the laser beam bypasses the gain medium and return to the first curved mirror, thereby completing a cycle of a ring traversed by the laser beam. The mask defines at least one beam-clipping aperture through which the laser beam passes during a cycle. The gain medium is pumped, preferably using a suitable pumping laser.