라만 산란이란 무엇입니까??-이노

The nonlinear response of a transparent optical medium to the optical intensity of light traveling through the medium is very fast, but not instantaneous. 특히, the non-instantaneous response is caused by vibrations in the lattice (or glass). When these vibrations are associated with optical phonons, the effect is called Raman scattering, while acoustic phonons are associated with Brillouin scattering. 예를 들어, when two laser beams with different wavelengths (usually with the same direction of polarization) propagate together through a Raman-active medium, the longer wavelength beam (called a Stokes wave)) can be optically amplified at the expense of the shorter wavelength beam. 게다가, the lattice vibrations are excited, 온도 상승으로 이어진다. The Raman gain of longer wavelength beams can be utilized in Raman amplifiers and Raman lasers. The gain may be substantial if the Stokes frequency shift corresponds to a frequency difference of a few terahertz.

Raman scattering can occur not only in solid materials, but also in liquids or gases. 예를 들어, molecular glasses have vibrational/rotational excitations and the observed Stokes shifts are correlated with those.

During Raman scattering, a pump photon is converted into a signal photon of lower energy, and the difference in photon energy is carried away by phonons (quanta of lattice vibrations). 원칙적으로, an already existing phonon may also interact with the pump photon to produce a higher energy photon that belongs to a shorter wavelength anti-Stokes wave. 하지만, the process is usually weak, especially at low temperatures. 메모, 하지만, 프로세스가 위상 일치되면 4파 혼합도 강력한 반스토크스 광을 생성합니다..

결과적으로 발생하는 스톡스파의 강도가 충분히 높아질 때, 파동은 추가 라만 프로세스를 위한 펌프 역할을 다시 수행할 수 있습니다.. 특히 일부 라만 레이저에서는, 여러 Stokes 주문을 관찰할 수 있습니다. (캐스케이드 라만 레이저).

라만 산란은 비탄성 산란으로도 알려져 있는데, 그 이유는 관련된 광자 에너지의 손실이 기계 물체의 충돌 시 운동 에너지의 손실을 연상시키기 때문입니다..

위의 흥분된 라만 산란 효과 외에도, 고전 물리학으로 설명할 수 있는 것, 양자 효과로 인한 자발적인 라만 산란도 있습니다..

라만 산란은 광범위한 스펙트럼 내에서도 발생할 수 있습니다., 예를 들어, 초단광 펄스, thus effectively shifting the spectral envelope of the pulse to longer wavelengths (Raman self-frequency shift, also known as soliton self-frequency shift).

Some typical Raman-active media are

Certain molecular gases, 수소와 같은 (시간 2 ), 메탄 (CH 4 ), 그리고 이산화탄소 (콜로라도 2 ), used in the high-voltage cell of a Raman shifter
Solid media such as glass fibers or certain crystals such as barium nitride = Ba(아니요 3)2, various tungstates such as KGd(WO 4)2 = KGW and KY(WO 4)2 = KYW, and synthetic diamonds

The Raman effect occurs simultaneously with the Kerr effect, which is due to the (almost) instantaneous response of electrons.

수치 1: Evolution of the pulse spectrum in a fiber-optic amplifier. Near the right end, excited Raman scattering shifts a large fraction of the power into longer wavelength components. As part of the case study, simulations were performed using the software RP Fiber Power.
수치 2: Optical power evolution in a parabolic refractive index multimode fiber, simulated as part of a case study by the digital beam propagation feature of the software RP Fiber Power. The signal wave is strongly amplified while the pump wave is severely depleted. The conversion process involves multiple modes.

In fiber optic devices such as strongly pulsed fiber amplifiers, Raman scattering can be detrimental: it diverts most of the pulse energy into wavelength ranges where no laser amplification occurs. This effect may limit the peak power achievable in such devices. Even in continuous-wave high-power fiber lasers and amplifiers, Raman scattering can be a problem. 하지만, there are several solutions to this problem, including chi pulse amplification and the use of special fiber designs) that suppress Raman scattering by attenuating the wavelength component of the Raman shift.

In bulk media such as some nonlinear crystalline materials, if the pump intensity is quite high and the beam width is sufficiently large, undesired excited Raman scattering can occur even by noncollinear phase matching. This may occur, 예를 들어, in an optical parameter generator operating with a strong pump pulse.

Raman scattering is also used in Raman spectroscopy. 특히, it allows one to study the vibrational modes of solid materials and the vibrational/rotational states of molecules.