Search

We experimentally investigate the high-order harmonic generation in argon gas cell driven by a multi-cycle broadband infrared laser pulse from a tunable optical-parametric-amplifier (OPA) source. The generation of high-order harmonic continuum with the cut-off photon energy up to 110 eV is observed by tuning the chirp of the 800-nm laser pulse which pumps OPA source. The generation of harmonic continuum is understood in terms of the two-hump structure of the OPA output spectrum and the optimal relative phase of the two humps. The demonstrated scheme is of importance for the generation of extreme ultraviolet (XUV) continuum at higher photon energy region.

Two different pulse cleaning techniques for ultra-high contrast laser systems are comparably analysed in this work. The first pulse cleaning technique is based on noncollinear femtosecond optical-parametric amplification (NOPA) and second-harmonic generation (SHG) processes. The other is based on cross-polarized wave (XPW) generation. With a double chirped pulse amplifier (double-CPA) scheme, although temporal contrast enhancement in a high-intensity femtosecond Ti:sapphire chirped pulse amplification (CPA) laser system can be achieved based on both of the techniques, the two different pulse cleaning techniques still have their own advantages and are suitable for different contrast enhancement requirements of different laser systems.

Employing a novel front-end based on femtosecond noncollinear optical-parametric amplification and second-harmonic generation processes in a Ti:sapphire chirped pulse amplification laser system, we first demonstrate the efficient enhancement of amplified spontaneous emission (ASE) contrast. Cleaned seed pulses of 100-μJ energy generated by the front-end are amplified to 0.75 J before compressor. After compression and under pulse peak power of 7 TW, the ASE contrast is promoted from original ~ 108 to ~ 1011. The experimental results for nanometer film target interactions also demonstrate the improvement of the contrast. Finally, the evolution of the ASE contrast under different seed pulse energy is demonstrated experimentally, which can be used to design the higher power laser with higher ASE contrast.

The hollow-core fiber structure influence of few-cycle pulse compressor on pulse contrast is investigated experimentally. It is found that a periodic structure of pulses at the tail of the main pulse extended hundreds of picoseconds away. It can be due to the fiber structure and could be eliminated by modifying the structure.

We demonstrate a 100 μJ

Generation of carrier-envelope phase stabilized 0.54 mJ, 9.3 fs pulses at 1.8 μm is demonstrated. The input pulse is spectrally broadened in an argon-filled hollow-core fiber, subsequently compressed in glass plates with anomalous dispersion.

A novel tunable phase-stabilized infrared femtosecond source was developed with CEP stabilization and >1mJ pulse energy. Based on the laser source, a novel pulse clean technique is developed, and the 1011 contrast ratio is demonstrated.

We demonstrate what we believe to be a novel tunable IR optical parametric amplifier (OPA) with the passively stabilized carrier-envelope phase (CEP), in which a hollow fiber is used to improve the output beam quality and to overcome the spatial chirp issue. Pumped by an 800 nm pump source, the output pulses are tunable from 1.2 to 2.4 microm with the CEP stabilization. The maximum output average energy can reach approximately (1.2 W/40 fs)/1 kHz with the total of (6.8 W/40 fs)/1 kHz pump energy. Further, the high-order harmonic generation driven by the tunable phase-stabilized OPA has been demonstrated.

This paper was presented at the SPIE conference indicated above but inadvertently published by SPIE subsequent to its publication in another journal (Optics Letters). The paper has therefore been withdrawn from the SPIE Proceedings by the author and the publisher. The journal paper can be accessed at http://dx.doi.org/10.1364/OL.34.002730.

Single-mode, continuous-wave, electrically-injected, GaSb based, 2.1 mum, equilateral-triangle-resonator lasers with a wavelength tuning range of 3.25 nm are demonstrated at 77 K.

A pulse clean technique in time domain combining noncollinear optical-parametric amplification and second-harmonic generation is demonstrated. The measurement-limited10(10) temporal contrast ratio of the 0.5 mJ/40 fs pulse near 800 nm is obtained over a large temporal range extending from1 ps before the main pulse. The contrast ratio enhancement as fourth power of the initial contrast is demonstrated. The total efficiency is6% for the 8.2 mJ/40 fs initial incident femtosecond pulse.

We experimentally investigate the high harmonic generation (HHG) from CH4 molecules and Xe atoms in a two-color field (using the 800 nm laser and the tunable laser with the longer wavelength from 1500 nm to 1900 nm), and observe that the longer wavelength component can destructively suppress the HHG from CH4 molecules. By controlling the time delay between the two color laser pulses or tuning the laser intensity of the longer wavelength component, the suppressions of the HHG from CH4 molecules and the enhancements of the HHG from Xe atoms at the same laser condition are observed. The results indicate that the longer wavelength component around the molecular infrared absorption can suppress the molecular HHG process.

The influence on the level of amplified spontaneous emission (ASE) contrast resulting from the different seed pulse energies has been experimentally studied in a 10-TW-level femtosecond Ti:sapphire chirped pulse amplification laser. It is found that, with the seed pulse energy increasing, the ASE pedestal is suppressed more efficiently, and the ASE contrast is improved with a saturable tendency. The measurement of ~2×10-8 ASE contrast in the range of more than 50 ps before the main pulse is achieved in the laser.

We experimentally investigate the wavelength effect on high-order harmonic generation (HHG) in CH(4) molecules and Xe atoms driven by a tunable infrared parametric source, and observe that the molecular HHG around the vibrational resonance is more sensitive to the driver wavelength than HHG from an atomic gas with comparable ionization potential. The results can be attributed to the light nuclear motion induced by the driving laser field, and it becomes possible to control the proton vibration in the molecular HHG by tuning the infrared wavelength of the driving laser.

Theoretical calculations of the mode characteristics of an equilateral-triangle resonator (ETR) with a 10μm cavity side length show that the fundamental mode, with longitudinal mode index of 25, has a wavelength of 2.185μm and a longitudinal mode separation of 100nm. This mode has a quality factor (∼2×105) that is much larger than the first (∼5×104) and second (∼3×104) order modes, indicating that single fundamental mode lasing should be accessible over a broad wavelength tuning range. An electrically injected ETR based on this design is fabricated from an InGaAsSb∕AlGaAsSb∕GaSb, graded-index separate-confinement heterostructure, laser diode wafer with a 2.1μm emission wavelength. This device achieved single mode, continuous wave operation at 77K with a threshold current of 0.5mA and a single mode wavelength tuning range of 3.25nm, which is accomplished by varying the injection current from 0.5to6.0mA.