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114:. In gas high harmonics, a gas jet usually acts as the nonlinear media and the femtosecond laser pulse interacts with the gas to emit high harmonics. Hence, only one laser pulse is required in gas harmonics. However to generate high harmonics from plasma plumes, we require another laser pulse focused onto the surface of a solid target to create a plume of laser ablated plasma. This plasma plume acts as a nonlinear medium for the nonlinear interaction. Typically, a long
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etc. Presence of such resonances makes plasma harmonics very different from gas harmonics. The enhanced harmonic efficiency of a given harmonic order can be useful for the development of narrowband tabletop XUV light sources. These type of sources can be very helpful in various types of spectroscopy
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states present in the continuum. The first two steps remain the same i.e. the tunnel ionization and the acceleration of this tunnel ionized electron in the continuum. However, in the third step, this tunnel ionization electron gets trapped into the autoionizing state present in the continuum. This
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plasma was much higher as compared to its neighboring harmonics. This was quite surprising because this kind of effect was never seen in gas harmonics. Upon careful investigations, it was pointed out by the researchers that this harmonic enhancement happens when the energy of a particular harmonic
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of 1.52. The energy of this transition corresponds to 17th harmonic with 800 nm excitation wavelength. Similarly, in Indium, there exists a strong transition 4d5s ā 4d 5s 5p at 19.92 eV with a high gf value of 1.11. The energy of this transition corresponds to 13th harmonic with 800 nm
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In some plasma plumes, it was observed that the intensity of a certain harmonic order was exceptionally high as compared to its neighboring harmonics. For example, by using 800 nm femtosecond laser pulses, it was observed that with
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excitation wavelength. This enhancement in a particular harmonic order is most commonly known as
Resonant High Harmonic Generation (RH). Apart from tin and Indium, RH has been observed in many other plasmas such as
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31:
undergoes an interaction with a nonlinear media. A typical high order harmonic spectra contains frequency combs separated by twice the laser frequency. HHG is an excellent table top source of highly
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autoionizing state usually has a longer lifetime. Then in the fourth step, this trapped electron recombines radiatively with the parent ion (ground state) emitting resonantly enhanced high harmonic.
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When the electric field the ultrashort laser pulse undergoes the reversal of direction, this accelerated electron returns and recombines radiatively with the parent ion emitting high harmonics.
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To explain this enhancement in a given harmonic order, the former three-step model was modified and a new four-step model was introduced. This model takes into account the role of
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Since the tunnel ionization and recombination process is happening twice in every cycle of the excitation laser pulse, the HHG process has the capability to generate the
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order matches with a strong transition present in the plasma. For example, it was observed that in tin, there exists a very strong transition 4d 5s 5p P
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plasma, the intensity of 17th harmonic was an order of magnitude higher as compared to the intensity of its neighboring harmonics.
258:
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Strelkov, V. (2010). "Role of
Autoionizing State in Resonant High-Order Harmonic Generation and Attosecond Pulse Production".
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Suzuki, Masayuki (2006). "Anomalous enhancement of a single high-order harmonic by using a laser-ablation tin plume at 47nm".
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Ganeev, Rashid A. (2006). "Strong resonance enhancement of a single harmonic generated in the extreme ultraviolet range".
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Schematic of experimental setup for HHG measurement from the laser ablation plume pumped by femtosecond laser pulse.
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In Corkum's three-step model, the electron is treated as a free particle having no effect of the coulomb potential.
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HHG process can be very easily as well as intuitively explained by a simple three-step model originally proposed by
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Duffy, Grainne (2001). "4dā5p transitions in the extreme ultraviolet photoabsorption spectra of Sn II and Sn III".
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This tunnel ionized electron undergoes acceleration under the effect of laser pulse electric field.
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Duffy, Grainne (2001). "The photoabsorption spectrum of an indium laser produced plasma".
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Schematic diagram of four-step model to explain the resonant harmonic generation
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HHG spectra from tin ablation irradiated by a femtosecond laser pulse.
497:"High-order harmonic generation from the dressed autoionizing states"
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Similarly, it was seen that the intensity of 13th harmonic in
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Advances in Solid-State Lasers: Development and
Applications
363:"Coherent x-ray generation at 2.7nm using 25fs laser pulses"
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Journal of
Physics B: Atomic, Molecular and Optical Physics
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Journal of
Physics B: Atomic, Molecular and Optical Physics
259:"Plasma perspective on strong field multiphoton ionization"
415:"High-Order Harmonic Generation from Low-Density Plasma"
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laser pulse is used for the purpose of plasma creation.
306:"53-attosecond X-ray pulses reach the carbon K-edge"
76:upon interaction with the ultrashort laser pulse.
222:Ganeev, R.A (2015). "Why plasma harmonics?".
8:
54:Three step model of high-harmonic generation
163:at 26.27 eV and this transition has a high
110:HHG can happen both in gases as well as in
27:process taking place when a highly intense
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102:laser pulses as a source of excitation.
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713:Laser - The world's fastest flash
244:10.1070/QE2015v045n09ABEH015574
679:10.1103/PhysRevLett.104.123901
165:oscillator strength (gf value)
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98:bursts of radiation by using
617:10.1088/0953-4075/34/15/319
283:10.1103/PhysRevLett.71.1994
112:laser ablated plasma plumes
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644:10.1088/0953-4075/34/6/104
370:AIP Conference Proceedings
330:10.1038/s41467-017-00321-0
361:Rundquist, Andy (1998).
17:High Harmonic Generation
659:Physical Review Letters
263:Physical Review Letters
716:, retrieved 2023-10-16
708:, retrieved 2023-10-16
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29:ultrashort laser pulse
501:Nature Communications
495:Fareed, M. A (2017).
310:Nature Communications
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106:HHG from laser plasma
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574:10.1364/OL.31.001699
474:10.1364/OL.31.003306
257:Corkum, P.B (1993).
671:2010PhRvL.104l3901S
609:2001JPhB...34.3171D
566:2006OptL...31.1699G
521:10.1038/ncomms16061
513:2017NatCo...816061F
466:2006OptL...31.3306S
382:1998AIPC..426..296R
322:2017NatCo...8..186L
275:1993PhRvL..71.1994C
236:2015QuEle..45..785G
224:Quantum Electronics
36:extreme ultraviolet
413:Ozaki, T. (2010).
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70:outermost electron
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603:(15): 3171ā3178.
438:978-953-7619-80-0
269:(13): 1994ā1997.
74:tunnel ionization
25:nonlinear optical
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735:Nonlinear optics
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100:femtosecond
60:Paul Corkum
19:(HHG) is a
724:Categories
316:(1): 186.
206:References
116:picosecond
96:attosecond
72:undergoes
40:soft X-ray
507:: 16061.
174:manganese
62:in 1993.
687:20366535
582:16688266
539:28714468
482:17072405
348:28775272
291:10054556
178:antimony
170:chromium
33:coherent
667:Bibcode
605:Bibcode
562:Bibcode
530:5520015
509:Bibcode
462:Bibcode
378:Bibcode
339:5543167
318:Bibcode
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232:Bibcode
86:Step 3:
80:Step 2:
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152:indium
366:(PDF)
683:PMID
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478:PMID
433:ISBN
344:PMID
287:PMID
68:The
38:and
675:doi
663:104
640:doi
613:doi
570:doi
525:PMC
517:doi
470:doi
423:doi
394:hdl
386:doi
374:426
334:PMC
326:doi
279:doi
240:doi
161:5/2
157:3/2
129:tin
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