Synchronized generation of bright high-order harmonics using self-guided and chirped femtosecond laser pulses (original) (raw)
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Control of high harmonic generation processes using chirped and self-guided femtosecond laser pulses
2007
High-order harmonic generation in a long gas jet is controlled in the space and time domains using chirped and self-guided femtosecond laser pulses. Since high-order harmonic generation is intrinsically connected to the ionization process of harmonic generation medium, ionization effects on high-order harmonic generation should be properly understood and taken into account. Here, we present a method to control high-order harmonic generation process by controlling the propagation mode of intense femtosecond laser pulses through the ionizing medium. Experimental results and theoretical analysis show that self-guided and chirped laser pulses can optimize high-order harmonics for achieving high brightness, low beam divergence, and narrow spectral bandwidth.
Physical Review A, 2005
We present a time-dependent analysis of high-order harmonics generated by a self-guided femtosecond laser pulse propagating through a long gas jet. A three-dimensional model is used to calculate the harmonic fields generated by laser pulses, which only differ by the sign of their initial chirp. The time-frequency distributions of the single-atom dipole and harmonic field reveal the dynamics of harmonic generation in the cutoff. A time-dependent phase-matching calculation was performed, taking into account the self-phase modulation of the laser field. Good phase matching holds for only few optical cycles, being dependent on the electron trajectory. When the cutoff trajectory is phase matched, emitted harmonics are locked in phase and the emission intensity is maximized.
High brightness harmonic generation at 13�nm using self-guided and chirped femtosecond laser pulses
Applied Physics B: Lasers and Optics, 2004
We have optimized the brightness of high-order harmonics from a long neon gas jet using self-guided and chirped laser pulses. The self-guided and chirped laser pulses effectively reduced the ionization effects in space and time, producing bright high-order harmonics with narrow bandwidth. The brightness of the 61st harmonic was about 10 15 W/cm 2 /s rad with a bandwidth of 0.7Å.
Atoms
The generation of high-order harmonics in a semi-infinite cell by femtosecond laser pulses is a common practice for reliable coherent and low divergence XUV source beams for applications. Despite the relative simplicity of the experimental method, several phenomena coexist that affect the generated spectral and divergence characteristics of the high harmonic XUV frequency comb. The ionisation degree of the medium and the consequent plasma formation length imposes a spatiotemporal evolution of the fundamental EM field and XUV absorption. Varying the laser pulse chirp and the focusing conditions, as well as the gas density, we measured intense harmonic spectral and divergence variations attributed mainly to self-phase modulations of the laser EM field in the partially ionised medium. Additionally, low-divergence high harmonics are observed for certain laser chirp values attributed to the strong phase matching of only the short electron quantum path. Thus, a tunable, low divergent, and...
Coherent control of high-order harmonics generated with intense femtosecond laser pulses
The European Physical Journal D - Atomic, Molecular and Optical Physics, 2003
High-order harmonics were coherently controlled using chirped femtosecond laser pulses for the production of sharp and strong harmonics. As the laser intensity was increased above the saturation intensity for optical-field ionization, the laser chirp needed to suppress harmonic chirp in the plateau region changed from positive to negative. We showed that the modification of a laser chirp condition in a rapidly ionizing medium should be included for the proper coherent control of high-order harmonics, necessitating the integral treatment of the interaction between atoms and a driving laser pulse.
Coherent Control of High-Order Harmonics with Chirped Femtosecond Laser Pulses
Physical Review Letters, 2001
High-order harmonics were coherently controlled using chirped femtosecond laser pulses for the production of sharp and strong harmonics. As the laser intensity was increased above the saturation intensity for optical-field ionization, the laser chirp needed to suppress harmonic chirp in the plateau region changed from positive to negative. We showed that the modification of a laser chirp condition in a rapidly ionizing medium should be included for the proper coherent control of high-order harmonics, necessitating the integral treatment of the interaction between atoms and a driving laser pulse.
Generation of high-order spatially coherent harmonics from solid targets by femtosecond laser pulses
Physical Review A, 2000
This paper discusses the generation of high-order optical harmonics from solid targets using laser pulses of 35 and 120 femtoseconds. Harmonics up to the 35th order were observed. High conversion efficiency has been achieved, e.g., 10 Ϫ6 to the 10th harmonic. It is demonstrated that the harmonic emission is highly directional and that the harmonic efficiency decreases rapidly with increasing plasma scale length.
Optics Letters, 2014
We demonstrate unexpectedly strong second harmonic generation (SHG) in argon gas by use of spatio-temporally focused (SF) femtosecond laser pulses. The resulting SHG by the SF scheme at a 75 cm distance shows a significantly enhanced efficiency than that achieved with conventional focusing schemes, which offers a new promising possibility for standoff applications. Our theoretical calculations reasonably reproduce the experimental observations, which indicate that the observed SHG mainly originates from the gradient of non-uniform plasma dynamically controlled by the SF laser field.
Applied Physics B-lasers and Optics, 1997
We report the realization of a vacuum-ultraviolet radiation source based on high-order harmonic generation in noble-gas samples, operating at high repetition rate. In particular, we observed up to the 13th harmonic (λ=61 nm) of the fundamental frequency of a short pulse, high repetition rate titanium–sapphire laser after its interaction with a Xe gas jet. The effects of the propagation of the fundamental and harmonic beams through an ionized medium are studied by analysing the spectral profile of the 9th and 7th harmonics. Finally, we report a study of the dependence of the harmonic conversion efficiency on relative position of the focus and the gas target.
2009
The intensity enhancement of harmonics and change in harmonic profiles have been observed in a few plasma plumes (La, In, Mn) under variable phase modulation of Ti:sapphire laser pulses. It is seen that variation of relative harmonic intensities in the plateau region could be achieved by chirp variation of narrowband (ϳ10 nm bandwidth) radiation. The effect of the self-phase modulation (SPM) of broadband (ϳ20 nm bandwidth) laser radiation on the harmonic emission from nanoparticles, C 60 , and Ag plasma while passing through a glass slab is also studied. The observation of broadband harmonic emission and redshift in harmonic wavelengths for an unchirped laser pulse are explained in terms of SPM. The observation of blueshift of harmonic radiation with both positively and negatively chirped pulses was attributed to the different effects of SPM on the chirped pulses.