Generation and control of femtosecond pulses by molecular modulation

Sokolov, Alexei V.; Shverdin, M. Y.; Walker, Daniel A.; Yavuz, D. D.; Burzo, Andrea; Yin, G. Y.; Harris, S. E.

doi:10.1080/09500340410001731020

Cited by 66 publications

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References 44 publications

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“…Taking advantage of the high Raman gain of H2 in the ultraviolet (about 3 times larger than at 532 nm [9]), we generate a purely vibrational Raman comb extending from the VUV (184 nm) to the visible (478 nm) via stimulated Raman scattering (SRS) and molecular modulation [10][11][12][13]. The short-wavelength bands extend further into the VUV than in previous experiments using H2-filled kagomé-PCF with narrow-band pump lasers [14,15].…”

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Generation of a vacuum ultraviolet to visible Raman frequency comb in H_2-filled kagomé photonic crystal fiber

et al. 2016

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We report the generation of a purely vibrational Raman comb, extending from the vacuum ultraviolet (184 nm) to the visible (478 nm), in hydrogen-filled kagomé-style photonic crystal fiber pumped at 266 nm. Stimulated Raman scattering and molecular modulation processes are enhanced by higher Raman gain in the ultraviolet. Owing to the pressure-tunable normal dispersion landscape of the "fiber + gas" system in the ultraviolet, higher-order anti-Stokes bands are generated preferentially in higher-order fiber modes. The results pave the way towards tunable fiber-based sources of deep-and vacuum ultraviolet light for applications in, e.g., spectroscopy and biomedicine.Fiber delivery and frequency conversion in the ultraviolet are topics of much current interest [1,2].Step-index fibers with pure silica cores have proven unsuitable because their performance dramatically falls over time due to colorcenter-related optical damage, unless they are hydrogen loaded [3]. Recent alternatives such as fluoride fibers [4] partially resolve this problem, extending the usable wavelength range into the deep ultraviolet (DUV). Kagomé-style hollow-core photonic crystal fiber (kagomé-PCF) is excellent alternative, offering a very low light-glass overlap [5]. It has been used for stable long-term transmission of continuous-wave 280 nm DUV light [6]. Kagomé-PCFs also offer very broad spectral transmission windows, and when gas-filled provide an ideal system for nonlinear generation of light at many different wavelengths. For example, when pumped at near infrared wavelengths, broadband DUV and vacuum ultraviolet (VUV) light has been generated in gasfilled kagomé-PCF [7,8].In this Letter, we discuss the first frequency-conversion scheme involving a H2-filled kagomé-PCF pumped at 266 nm. Taking advantage of the high Raman gain of H2 in the ultraviolet (about 3 times larger than at 532 nm [9]), we generate a purely vibrational Raman comb extending from the VUV (184 nm) to the visible (478 nm) via stimulated Raman scattering (SRS) and molecular modulation [10][11][12][13]. The short-wavelength bands extend further into the VUV than in previous experiments using H2-filled kagomé-PCF with narrow-band pump lasers [14,15]. Moreover, the narrow Raman gain bandwidth, together with a narrow-band pump, results in Raman sidebands with high spectral power density-a distinct advantage over broadband sources, when it is necessary to use filters (not always available in the DUV and VUV) to select spectral bands. The system demonstrated here is very compact compared to free-space arrangements [16] and its potential tunability using different Raman-active gases makes it ideal for applications such as high-resolution spectroscopy, metrology and biology.In SRS a relatively strong pump pulse scatters off the molecules in the medium giving rise to a lower energy Stokes signal. The beat note of the pump and Stokes signals excites a Raman-active mode of the molecule (in our system, the fundamental vibrational mode of H2 with ΩR/2π ~ 125 THz). This process is acco...

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Generation of a vacuum ultraviolet to visible Raman frequency comb in H_2-filled kagomé photonic crystal fiber

et al. 2016

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“…1,2,4 As a result, the spectrum of n sidebands has two independent phases. Also, because the lowest frequency of the comb is offset from zero, the sidebands do not constitute a strict Fourier series, and the waveform is not periodic.…”

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“…Over the past several years it has been shown that molecular modulation can produce a collinear beam of mutually coherent sidebands that extend in frequency from the IR to the far UV. [1][2][3][4] Adjusting the phases of these sidebands allows periodic optical waveforms with a prescribed temporal shape to be synthesized. In early experiments the temporal shape of the synthesized waveforms was measured by using multiphoton ionization.…”

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Measurement of Fourier-synthesized optical waveforms

et al. 2005

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Following the experiments of Shverdin and colleagues [Phys. Rev. Lett. 94, 033904 (2005)], we describe a technique for determining the temporal envelope of an optical beam whose spectrum consists of n discrete, equally spaced frequency components. Four-wave mixing is employed to generate n − 1 higher-frequency sidebands. The relative intensities of these sidebands, together with the intensities of the incident sidebands, determine the unknown relative phases of the incident beam. © 2005 Optical Society of America OCIS codes: 190.4380, 320.7100, 320.7110. Over the past several years it has been shown that molecular modulation can produce a collinear beam of mutually coherent sidebands that extend in frequency from the IR to the far UV. [1][2][3][4] Adjusting the phases of these sidebands allows periodic optical waveforms with a prescribed temporal shape to be synthesized. In early experiments the temporal shape of the synthesized waveforms was measured by using multiphoton ionization. 5Recently, Shverdin et al.6 used a new technique for waveform characterization based on four-wave mixing of the type i + j − k . They described how n equally spaced Raman sidebands incident on a Xe cell will generate n − 1 higher-frequency (UV) sidebands that extend the incident comb of frequencies. Adjusting the relative phases of the incident sidebands and thereby shaping the incident temporal waveform dramatically altered the relative intensities of the UV sidebands. A train of single-cycle pulses maximized the UV intensity, FM-like waveforms minimized the intensity, and other waveforms produced particular relative intensity distributions. 6In this Letter we describe the inverse process: the use of the generated n − 1 component UV spectrum to determine the unknown relative phases of the primary spectrum. With the primary sidebands' amplitudes known, the incident temporal waveform is determined to within the carrier-envelope phase. This method is suited for multioctave waveforms with discrete sidebands, a regime not easily accessible with conventional methods such as frequency-resolved optical gating.7 Figure 1 depicts the experimental setup for the technique. The generated Raman sidebands are dispersed by a prism, individually phase corrected, and refocused into the target Xe cell. A photomultiplier tube measures the power of each of the generated UV sidebands. Because it allows focusing to the cell center, we use the nonlinear difference-frequency process i + j − k . (The alternative, a sum-frequency process of the type i + j + k , will have a much lower generation efficiency because of Gouy phase shift.8 ) To start, we assume that the incident Raman sideband frequencies extend to zero so that the frequency of the qth sideband is q = q v . We also assume that the relative phases of the sidebands are controlled. Figure 2 shows three temporal waveforms, their spectral amplitudes (square root of their powers), and the spectral amplitudes of the generated UV sidebands. As expected, the single-cycle (modelocked) waveform generate...

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“…In the near future, we envision driving one of these Raman transitions by a pair of timedelayed chirped picosecond pulses, and then using another (compressed or shaped) fs pulse from the same source laser, to probe the Raman coherence prepared by the two excitation pulses. Our experiment has already shown efficient spectral broadening of a (third) probe pulse; future experiments will possibly lead to substantial pulse compression in the same medium, as predicted in our earlier work (Sokolov & Harris, 2003;Sokolov et al, 2005). Whether the collinear generation in PbWO 4 crystal by the excitation of the small-frequency Raman mode at 325 cm −1 can be realized or not deserves to be studied, since collinear generation will result in the convenience of combining the sidebands for sub-fs pulse synthesis.…”

Section: Discussionmentioning

confidence: 63%

Broadband Light Generation in Raman-active Crystals Driven by Femtosecond Laser Fields

Zhi¹

2010

Advances in Lasers and Electro Optics

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Generation and control of femtosecond pulses by molecular modulation

Cited by 66 publications

References 44 publications

Generation of a vacuum ultraviolet to visible Raman frequency comb in H_2-filled kagomé photonic crystal fiber

Generation of a vacuum ultraviolet to visible Raman frequency comb in H_2-filled kagomé photonic crystal fiber

Measurement of Fourier-synthesized optical waveforms

Broadband Light Generation in Raman-active Crystals Driven by Femtosecond Laser Fields

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