[3분논문] 제29회 (마지막회) - 굴절률 0인 물질에서 비선형 현상

황용섭의 3분논문 제29회입니다.

총시간은 6분 23초입니다.

재미있게 들어보세요.

# 방송 바로 듣기

1. 29_3분논문_제29회.mp3

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팟캐스트 검색: "3분논문"

팟캐스트 주소: http://itunes.apple.com/us/podcast/3bunnonmun/id568397433

RSS 피드: http://www.iblug.com/xml/itunes/3minpaper.xml

# 논문표지

# 간단한 정보

글쓴이: Haim Suchowski, Kevin O’Brien, Zi Jing Wong, Alessandro Salandrino,

            Xiaobo Yin, Xiang Zhang

제목: Phase Mismatch–Free Nonlinear Propagation in Optical Zero-Index Materials

학술지: Science

발행년월: 2013년 12월 

이어가기: http://dx.doi.org/10.1126/science.1244303

# 용어

- zero-index material: 굴절률 0인 물질.

메타물질의 하나로, 광학적 굴절률이 0이 되도록 인공적으로 만든 물질이다.

- four wave mixing: 4파 섞임. 비선형 현상의 하나. 비선형 현상의 결과빛의 파장이 입사된 빛의 파장과 비슷하다. 

※방송에서 "degenerate four wave mixing"을 우리말로 옮기면서 "결맞는 4파 섞임"이라고 말했는데, "졸들은 4파 섞임" 또는 "겹친 4파 섞임"이라고 해야 맞습니다. 오류가 있었음에 사과 드립니다.

# 발췌

1. 

... the zero index eliminates the need for phase matching, allowing efficient nonlinear generation in both forward and backward directions.

2.

We demonstrate phase mismatch–free nonlinear generation using intrapulse four-wave mixing, where we observed a forward-to-backward nonlinear emission ratio close to unity. 

# 그림

Fig. 2. Experimental apparatus for nonlinear measurements.

(A) A transform-limited 100-fs laser pulse centered at 1315 nm or 1510 nm is amplitude-shaped through a spatial light modulator (SLM) to remove the long-wavelength tail of the pulse (red). The pulse is passed through a fishnet metamaterial, which generates a FWM nonlinear signal (green) in the backward and forward directions because of a third-order nonlinearity. The FWM signals are measured in an infrared spectrometer after filtering the pump pulse. The forward emission is measured without the flip mirror (M4). An analyzer is used before the spectrometer to control the detected polarization; a half-wave plate (not shown) controls the pump polarization. (B) An example measurement of the emission spectrum, showing both the generated FWM signal (green) and the filtered pump (red). The pump is undepleted by the nonlinear process, as evident by the much weaker FWM signal than that of the pump (the magnitude of the FWM is ~10⁻⁵ times the pump intensity), justifying the use of the perturbative approach in our analysis. (C) Scanning electron micrograph of the cross-fishnet structures. Inset shows an angled view. See supplementary materials for details of the single-shot FWM method.

Fig. 3. Four-wave mixing in metamaterials with and without phase mismatch.

(A) Phase mismatch of forward (purple) and backward (blue) FWM as a function of wavelength, based on experimentally measured refractive indices. The forward phase mismatch is near zero (Δk₊→ 0) for all wavelengths; the backward has a large phase mismatch (Δk_– ≠ 0) except when the index is near zero. (B) The measured FWM process in the zero-index regime has almost the same yield in both directions, illustrating the phase mismatch–free properties of zero-index materials. (C) In contrast, the forward-propagating FWM (solid purple) is much stronger than the backward (dashed blue) in the negative-index regime as a result of the phase mismatch. Insets in (B) and (C) show the dependence of the nonlinear emission (with a horizontally polarized analyzer) on pump polarization, which has the characteristic cos⁶ θ curve of χ⁽³⁾ dynamics. The nonlinear emission scales with the cube of the pump power and shows a spectral phase dependence demonstrating the nonlinear origin (fig. S6).

# 결론

굴절률 0인 메타물질을 이용해서 위상 어긋남으로부터 자유로운 비선형물질을 만들었다. 아이디어도 좋고, 실험적으로 구현하기 까다로운 부분이 많았을텐데 그걸 잘 해결해서 좋은 논문이 되었다. 

# 덧붙여

그 동안 들어주셔서 고맙습니다. 개인적인 사정으로 29회를 마지막으로 3분논문을 마칩니다. 앞으로 다른 기회에 다른 형태로 만날 수 있게 되리라 생각합니다. 하시는 연구 모두 잘 되길 바랍니다.

끝.

2014년 1월 16일