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Route to optimal generation of soft X-ray high harmonics with synthesized two-color laser pulses.

Jin C, Wang G, Le AT, Lin CD - Sci Rep (2014)

Bottom Line: Here we show that the conversion efficiency may be drastically increased with an optimized two-color pulse.By employing an optimally synthesized 2-µm mid-infrared laser and a small amount of its third harmonic, we show that harmonic yields from sub- to few-keV energy can be increased typically by ten-fold over the optimized single-color one.By combining with favorable phase-matching and together with the emerging high-repetition MHz mid-infrared lasers, we anticipate efficiency of harmonic yields can be increased by four to five orders in the near future, thus paving the way for employing high harmonics as useful broadband tabletop light sources from the extreme ultraviolet to the X-rays, as well as providing new tools for interrogating ultrafast dynamics of matter at attosecond timescales.

View Article: PubMed Central - PubMed

Affiliation: J. R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA.

ABSTRACT
High harmonics extending to X-rays have been generated from gases by intense lasers. To establish these coherent broadband radiations as an all-purpose tabletop light source for general applications in science and technology, new methods are needed to overcome the present low conversion efficiencies. Here we show that the conversion efficiency may be drastically increased with an optimized two-color pulse. By employing an optimally synthesized 2-µm mid-infrared laser and a small amount of its third harmonic, we show that harmonic yields from sub- to few-keV energy can be increased typically by ten-fold over the optimized single-color one. By combining with favorable phase-matching and together with the emerging high-repetition MHz mid-infrared lasers, we anticipate efficiency of harmonic yields can be increased by four to five orders in the near future, thus paving the way for employing high harmonics as useful broadband tabletop light sources from the extreme ultraviolet to the X-rays, as well as providing new tools for interrogating ultrafast dynamics of matter at attosecond timescales.

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Macroscopic spectra with two-color waveforms.(a) Macroscopic HHG spectra of Ne by using optimized waveforms to generate three different cutoff energies. The corresponding maximum returning electron energies are 150, 250 and 350 eV, using fundamental wavelengths of 1075, 1367 and 1625 nm, respectively. The total intensity is about 4.2 × 1014 W cm−2, with the third harmonic about 10% of the intensity of the fundamental. Laser parameters are from Table 2. (b) Macroscopic HHG spectra generated from He with maximum returning electron energy of 500 eV, for the synthesized wave as compared to the single-color wave. The third harmonic intensity is about 5% of the fundamental wave which has wavelength of 1422 nm. The total peak intensity is about 7.8 × 1014 W cm−2. Other laser parameters are given in Table 3.
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f3: Macroscopic spectra with two-color waveforms.(a) Macroscopic HHG spectra of Ne by using optimized waveforms to generate three different cutoff energies. The corresponding maximum returning electron energies are 150, 250 and 350 eV, using fundamental wavelengths of 1075, 1367 and 1625 nm, respectively. The total intensity is about 4.2 × 1014 W cm−2, with the third harmonic about 10% of the intensity of the fundamental. Laser parameters are from Table 2. (b) Macroscopic HHG spectra generated from He with maximum returning electron energy of 500 eV, for the synthesized wave as compared to the single-color wave. The third harmonic intensity is about 5% of the fundamental wave which has wavelength of 1422 nm. The total peak intensity is about 7.8 × 1014 W cm−2. Other laser parameters are given in Table 3.

Mentions: In Fig. 1 we show the minimum wavelength needed to reach a certain harmonic cutoff energy. Within the same photon energy region, can a longer wavelength (together with its third harmonic) generate more intense harmonics? In Fig. 3(a), we compare the macroscopic HHG spectra of Ne for three different cutoff energies. (Similar single-color results are shown in Supplementary Fig. S2, and single-atom HHG spectra of two-color waveforms are shown in Supplementary Fig. S3.) These spectra are generated by waveforms with fundamental wavelengths of 1075, 1367 and 1625 nm in order of increasing cutoff energy, respectively. Macroscopic conditions used to generate macroscopic HHG spectra are similar to Fig. 2. It is clear that the HHG yields drop rapidly when the harmonic cutoff energy is extended, or equivalently, when longer wavelength lasers are used. With the wavelength increases from 1075 nm to 1625 nm, i.e., by a factor of 1.5, the low-energy harmonics up to 150 eV drop by a factor of 125. Note that this result is based on the macroscopic conditions used in the simulation. If one is only interested in harmonics up to 150 eV with a longer wavelength laser, higher gas pressure can be used. For single-color laser an enhancement factor of 10 has been reported11 if the pressure is optimized. Nevertheless, it is preferable to use the shortest wavelength laser to generate harmonics for each photon energy range as depicted in Fig. 1.


Route to optimal generation of soft X-ray high harmonics with synthesized two-color laser pulses.

Jin C, Wang G, Le AT, Lin CD - Sci Rep (2014)

Macroscopic spectra with two-color waveforms.(a) Macroscopic HHG spectra of Ne by using optimized waveforms to generate three different cutoff energies. The corresponding maximum returning electron energies are 150, 250 and 350 eV, using fundamental wavelengths of 1075, 1367 and 1625 nm, respectively. The total intensity is about 4.2 × 1014 W cm−2, with the third harmonic about 10% of the intensity of the fundamental. Laser parameters are from Table 2. (b) Macroscopic HHG spectra generated from He with maximum returning electron energy of 500 eV, for the synthesized wave as compared to the single-color wave. The third harmonic intensity is about 5% of the fundamental wave which has wavelength of 1422 nm. The total peak intensity is about 7.8 × 1014 W cm−2. Other laser parameters are given in Table 3.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4233338&req=5

f3: Macroscopic spectra with two-color waveforms.(a) Macroscopic HHG spectra of Ne by using optimized waveforms to generate three different cutoff energies. The corresponding maximum returning electron energies are 150, 250 and 350 eV, using fundamental wavelengths of 1075, 1367 and 1625 nm, respectively. The total intensity is about 4.2 × 1014 W cm−2, with the third harmonic about 10% of the intensity of the fundamental. Laser parameters are from Table 2. (b) Macroscopic HHG spectra generated from He with maximum returning electron energy of 500 eV, for the synthesized wave as compared to the single-color wave. The third harmonic intensity is about 5% of the fundamental wave which has wavelength of 1422 nm. The total peak intensity is about 7.8 × 1014 W cm−2. Other laser parameters are given in Table 3.
Mentions: In Fig. 1 we show the minimum wavelength needed to reach a certain harmonic cutoff energy. Within the same photon energy region, can a longer wavelength (together with its third harmonic) generate more intense harmonics? In Fig. 3(a), we compare the macroscopic HHG spectra of Ne for three different cutoff energies. (Similar single-color results are shown in Supplementary Fig. S2, and single-atom HHG spectra of two-color waveforms are shown in Supplementary Fig. S3.) These spectra are generated by waveforms with fundamental wavelengths of 1075, 1367 and 1625 nm in order of increasing cutoff energy, respectively. Macroscopic conditions used to generate macroscopic HHG spectra are similar to Fig. 2. It is clear that the HHG yields drop rapidly when the harmonic cutoff energy is extended, or equivalently, when longer wavelength lasers are used. With the wavelength increases from 1075 nm to 1625 nm, i.e., by a factor of 1.5, the low-energy harmonics up to 150 eV drop by a factor of 125. Note that this result is based on the macroscopic conditions used in the simulation. If one is only interested in harmonics up to 150 eV with a longer wavelength laser, higher gas pressure can be used. For single-color laser an enhancement factor of 10 has been reported11 if the pressure is optimized. Nevertheless, it is preferable to use the shortest wavelength laser to generate harmonics for each photon energy range as depicted in Fig. 1.

Bottom Line: Here we show that the conversion efficiency may be drastically increased with an optimized two-color pulse.By employing an optimally synthesized 2-µm mid-infrared laser and a small amount of its third harmonic, we show that harmonic yields from sub- to few-keV energy can be increased typically by ten-fold over the optimized single-color one.By combining with favorable phase-matching and together with the emerging high-repetition MHz mid-infrared lasers, we anticipate efficiency of harmonic yields can be increased by four to five orders in the near future, thus paving the way for employing high harmonics as useful broadband tabletop light sources from the extreme ultraviolet to the X-rays, as well as providing new tools for interrogating ultrafast dynamics of matter at attosecond timescales.

View Article: PubMed Central - PubMed

Affiliation: J. R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA.

ABSTRACT
High harmonics extending to X-rays have been generated from gases by intense lasers. To establish these coherent broadband radiations as an all-purpose tabletop light source for general applications in science and technology, new methods are needed to overcome the present low conversion efficiencies. Here we show that the conversion efficiency may be drastically increased with an optimized two-color pulse. By employing an optimally synthesized 2-µm mid-infrared laser and a small amount of its third harmonic, we show that harmonic yields from sub- to few-keV energy can be increased typically by ten-fold over the optimized single-color one. By combining with favorable phase-matching and together with the emerging high-repetition MHz mid-infrared lasers, we anticipate efficiency of harmonic yields can be increased by four to five orders in the near future, thus paving the way for employing high harmonics as useful broadband tabletop light sources from the extreme ultraviolet to the X-rays, as well as providing new tools for interrogating ultrafast dynamics of matter at attosecond timescales.

No MeSH data available.


Related in: MedlinePlus