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Strong sub-terahertz surface waves generated on a metal wire by high-intensity laser pulses.

Tokita S, Sakabe S, Nagashima T, Hashida M, Inoue S - Sci Rep (2015)

Bottom Line: Here, ultrafast field propagation along a metal wire driven by a femtosecond laser pulse with an intensity of 10(18) W/cm(2) is characterized by femtosecond electron deflectometry.From experimental and numerical results, we conclude that the field propagating at the speed of light is a half-cycle transverse-magnetic surface wave excited on the wire and a considerable portion of the kinetic energy of laser-produced fast electrons can be transferred to the sub-surface wave.The peak electric field strength of the surface wave and the pulse duration are estimated to be 200 MV/m and 7 ps, respectively.

View Article: PubMed Central - PubMed

Affiliation: 1] Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan [2] Department of Physics, Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo, Kyoto 606-7501, Japan.

ABSTRACT
Terahertz pulses trapped as surface waves on a wire waveguide can be flexibly transmitted and focused to sub-wavelength dimensions by using, for example, a tapered tip. This is particularly useful for applications that require high-field pulses. However, the generation of strong terahertz surface waves on a wire waveguide remains a challenge. Here, ultrafast field propagation along a metal wire driven by a femtosecond laser pulse with an intensity of 10(18) W/cm(2) is characterized by femtosecond electron deflectometry. From experimental and numerical results, we conclude that the field propagating at the speed of light is a half-cycle transverse-magnetic surface wave excited on the wire and a considerable portion of the kinetic energy of laser-produced fast electrons can be transferred to the sub-surface wave. The peak electric field strength of the surface wave and the pulse duration are estimated to be 200 MV/m and 7 ps, respectively.

No MeSH data available.


Related in: MedlinePlus

Detection of electromagnetic waves emitted from the end of a wire of 500 mm in length, using a deuterated triglycine sulfate (DTGS) pyroelectric detector.(a) Experimental layout for radiation detection. (PTFE: polytetrafluoroethylene. PMMA: Poly(methyl methacrylate).) The distance from the laser-irradiated spot to the end of the wire is about 450 mm, and the distance from the end of the wire to the pyroelectric detector is 50 mm. A black polypropylene sheet is put over the detector window to block scattered light. (b) Angular distribution of radiation with horizontal and vertical polarizations in the horizontal plane. The incident laser pulse energy is 80 mJ. (c) Dependence of signal on laser pule energy at 20° for horizontal polarization. The solid line is a parabola (y = a·x2) fitted to the experimental data, which are indicated by the diamond symbols.
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f5: Detection of electromagnetic waves emitted from the end of a wire of 500 mm in length, using a deuterated triglycine sulfate (DTGS) pyroelectric detector.(a) Experimental layout for radiation detection. (PTFE: polytetrafluoroethylene. PMMA: Poly(methyl methacrylate).) The distance from the laser-irradiated spot to the end of the wire is about 450 mm, and the distance from the end of the wire to the pyroelectric detector is 50 mm. A black polypropylene sheet is put over the detector window to block scattered light. (b) Angular distribution of radiation with horizontal and vertical polarizations in the horizontal plane. The incident laser pulse energy is 80 mJ. (c) Dependence of signal on laser pule energy at 20° for horizontal polarization. The solid line is a parabola (y = a·x2) fitted to the experimental data, which are indicated by the diamond symbols.

Mentions: Since the propagation loss of the wire waveguide in the gigahertz to terahertz frequency range is low (e.g., 2 dB/m at 100 GHz (theoretical value)), the generated surface wave can be transmitted over a long wire. As shown in Fig. 5(a), if a tungsten wire of 500 mm in length is irradiated with 150 fs laser pulses in a vacuum, then the generated surface wave can be guided into the atmosphere via a wire transmission line spanning a distance of about 450 mm. The surface wave is reflected at the end of the wire, but there will be partial emission of an electromagnetic wave into free space. The strength and polarization of the emitted wave is detected by using a deuterated triglycine sulfate (DTGS) pyroelectric detector with a terahertz wire-grid polarizer. The measured angular distributions of radiation with horizontal and vertical polarizations in the horizontal plane are shown in Fig. 5(b). The signals of the vertically polarized components are comparable to the noise level, while the signals of the horizontally polarized components are strong between 10° and 40° and between −10° and −40°. In contrast, in the vertical plane, strong vertical signals and weak horizontal signals were observed in additional experiments. These results indicate that the detected radiation has a radial polarization originating from the Sommerfeld surface wave. Figure 5(c) shows the dependence of the signal on laser pulse energy at 20° for the horizontally polarized component. The signal intensity is proportional to the square of laser pulse energy and the signal does not saturate at the maximum laser pulse energy of 285 mJ. From the ratio of the signals at 70 and 285 mJ, we estimate that the total energy of the surface wave reaches approximately 5 mJ at the maximum laser pulse energy, resulting a conversion efficiency of approximately 1.7%.


Strong sub-terahertz surface waves generated on a metal wire by high-intensity laser pulses.

Tokita S, Sakabe S, Nagashima T, Hashida M, Inoue S - Sci Rep (2015)

Detection of electromagnetic waves emitted from the end of a wire of 500 mm in length, using a deuterated triglycine sulfate (DTGS) pyroelectric detector.(a) Experimental layout for radiation detection. (PTFE: polytetrafluoroethylene. PMMA: Poly(methyl methacrylate).) The distance from the laser-irradiated spot to the end of the wire is about 450 mm, and the distance from the end of the wire to the pyroelectric detector is 50 mm. A black polypropylene sheet is put over the detector window to block scattered light. (b) Angular distribution of radiation with horizontal and vertical polarizations in the horizontal plane. The incident laser pulse energy is 80 mJ. (c) Dependence of signal on laser pule energy at 20° for horizontal polarization. The solid line is a parabola (y = a·x2) fitted to the experimental data, which are indicated by the diamond symbols.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4317702&req=5

f5: Detection of electromagnetic waves emitted from the end of a wire of 500 mm in length, using a deuterated triglycine sulfate (DTGS) pyroelectric detector.(a) Experimental layout for radiation detection. (PTFE: polytetrafluoroethylene. PMMA: Poly(methyl methacrylate).) The distance from the laser-irradiated spot to the end of the wire is about 450 mm, and the distance from the end of the wire to the pyroelectric detector is 50 mm. A black polypropylene sheet is put over the detector window to block scattered light. (b) Angular distribution of radiation with horizontal and vertical polarizations in the horizontal plane. The incident laser pulse energy is 80 mJ. (c) Dependence of signal on laser pule energy at 20° for horizontal polarization. The solid line is a parabola (y = a·x2) fitted to the experimental data, which are indicated by the diamond symbols.
Mentions: Since the propagation loss of the wire waveguide in the gigahertz to terahertz frequency range is low (e.g., 2 dB/m at 100 GHz (theoretical value)), the generated surface wave can be transmitted over a long wire. As shown in Fig. 5(a), if a tungsten wire of 500 mm in length is irradiated with 150 fs laser pulses in a vacuum, then the generated surface wave can be guided into the atmosphere via a wire transmission line spanning a distance of about 450 mm. The surface wave is reflected at the end of the wire, but there will be partial emission of an electromagnetic wave into free space. The strength and polarization of the emitted wave is detected by using a deuterated triglycine sulfate (DTGS) pyroelectric detector with a terahertz wire-grid polarizer. The measured angular distributions of radiation with horizontal and vertical polarizations in the horizontal plane are shown in Fig. 5(b). The signals of the vertically polarized components are comparable to the noise level, while the signals of the horizontally polarized components are strong between 10° and 40° and between −10° and −40°. In contrast, in the vertical plane, strong vertical signals and weak horizontal signals were observed in additional experiments. These results indicate that the detected radiation has a radial polarization originating from the Sommerfeld surface wave. Figure 5(c) shows the dependence of the signal on laser pulse energy at 20° for the horizontally polarized component. The signal intensity is proportional to the square of laser pulse energy and the signal does not saturate at the maximum laser pulse energy of 285 mJ. From the ratio of the signals at 70 and 285 mJ, we estimate that the total energy of the surface wave reaches approximately 5 mJ at the maximum laser pulse energy, resulting a conversion efficiency of approximately 1.7%.

Bottom Line: Here, ultrafast field propagation along a metal wire driven by a femtosecond laser pulse with an intensity of 10(18) W/cm(2) is characterized by femtosecond electron deflectometry.From experimental and numerical results, we conclude that the field propagating at the speed of light is a half-cycle transverse-magnetic surface wave excited on the wire and a considerable portion of the kinetic energy of laser-produced fast electrons can be transferred to the sub-surface wave.The peak electric field strength of the surface wave and the pulse duration are estimated to be 200 MV/m and 7 ps, respectively.

View Article: PubMed Central - PubMed

Affiliation: 1] Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan [2] Department of Physics, Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo, Kyoto 606-7501, Japan.

ABSTRACT
Terahertz pulses trapped as surface waves on a wire waveguide can be flexibly transmitted and focused to sub-wavelength dimensions by using, for example, a tapered tip. This is particularly useful for applications that require high-field pulses. However, the generation of strong terahertz surface waves on a wire waveguide remains a challenge. Here, ultrafast field propagation along a metal wire driven by a femtosecond laser pulse with an intensity of 10(18) W/cm(2) is characterized by femtosecond electron deflectometry. From experimental and numerical results, we conclude that the field propagating at the speed of light is a half-cycle transverse-magnetic surface wave excited on the wire and a considerable portion of the kinetic energy of laser-produced fast electrons can be transferred to the sub-surface wave. The peak electric field strength of the surface wave and the pulse duration are estimated to be 200 MV/m and 7 ps, respectively.

No MeSH data available.


Related in: MedlinePlus