二维LiNbO3非线性光子晶体中的四次谐波产生

166 浏览量更新于2024-08-27 收藏 561KB PDF 举报

"本文详细探讨了利用二维LiNbO3非线性光子晶体进行中红外超短脉冲的四次谐波生成现象。研究中，科研人员观察到五束锥形谐波束，这些谐波束来源于1997纳米波长的飞秒中红外脉冲与具有Sierpinski分形超晶格结构的2D LiNbO3非线性光子晶体的相互作用。主要的衍射阶数和参与交互的相应倒格矢被确定。第二和第三谐波分别在23.82°和36.75°的外部角度产生，这归因于非线性的Cerenkov和Bragg衍射。同时，观察到了三种四次谐波生成路径，它们分别在14.21°、36.5°和53.48°的外部角度出现，其中第一种是由于非线性Cerenkov衍射产生的。" 在光学领域，非线性光学是研究光与物质相互作用时，光的强度如何影响物质响应的学科。在这个实验中，研究者使用了二维的LiNbO3（铌酸锂）非线性光子晶体，这是一种具有优异非线性光学特性的材料。非线性光子晶体是由周期性排列的单元组成，可以控制光的传播和相互作用，尤其在非线性光学过程中，如谐波生成。四次谐波生成是非线性光学的一个重要过程，它涉及到将输入的光波频率转换为其四倍。在这个实验中，通过使用中红外的超短脉冲，研究人员能够观察到这一过程。超短脉冲具有极高的峰值功率，能够激发材料中的强非线性效应。输入的1997纳米波长的脉冲在与2D LiNbO3非线性光子晶体相互作用后，产生了多种谐波，包括第二、第三以及第四次谐波。 Cerenkov衍射和Bragg衍射是两种不同的光衍射现象。Cerenkov辐射通常发生在介质中光速超过电子速度时，而在这里是非线性版本，即非线性Cerenkov衍射，它涉及光场与物质的非线性相互作用，导致频率的改变。另一方面，Bragg衍射是晶体对光的散射，当入射光的波长与晶格间距相匹配时，会产生特定角度的反射。 Sierpinski分形超级晶格的引入增加了实验的复杂性和潜在的应用价值。这种结构的非线性光子晶体能够提供更丰富的光与物质相互作用的可能性，可能用于开发新型的光子器件，例如频率转换器、光谱分析仪或激光技术。这项研究揭示了非线性光子晶体在中红外波段的潜力，特别是对于高次谐波生成的应用。通过深入理解这些非线性效应和它们在特殊结构中的表现，科学家们可以设计出更高效的光子学设备，这对于量子信息处理、光子计算和超快光学等领域具有重要意义。

Fourth-harmonic generation via nonlinear diffraction in a

2D LiNbO

nonlinear photonic crystal from mid-IR

ultrashort pulses

Boqin Ma (马博琴)

1,2,

*, Kyle Kafka

, and Enam Chowdhury

Faculty of Science and Technology, Communication University of China, Beijing 100024, China

Department of Physics, Ohio State University, Columbus, Ohio 43210, USA

*Corresponding author: maboqin@cuc.edu.cn

Received October 16, 2016; accepted February 10, 2017; posted online March 13, 2017

Five conical harmonic beams are generated from the interaction of femtosecond mid-infrared (mid-IR) pulses at

a nominal input wavelength of 1997 nm with a 2D LiNbO

nonlinear photonic crystal with Sierpinski fractal

superlattices. The main diffraction orders and the corresponding reciprocal vectors involved in the interaction

are ascertained. Second and third harmonics emerging at external angles of 23.82° and 36.75° result from non-

linear

Cerenkov and Bragg diffractions, respectively. Three pathways of fourth-harmonic generation are

observed at external angles of 14.21°, 36.5°, and 53.48°, with the first one resulting from nonlinear

Cerenkov

diffraction, and the other two harmonics are generated via different cascaded processes.

OCIS codes: 190.4420, 190.2620, 050.1940.

doi: 10.3788/COL201715.051901.

When a monochromatic wave passes through a homo-

geneous medium with its second-order nonlinear suscep-

tibility varying in some regions, e.g., χ

ð2Þ

in a nonlinear

photonic crystal (NPC), nonlinear diffraction can be

detected for the harmonic rings or spots of the input fun-

damental wave

[1–6]

. Nonlinear diffraction, which is based on

phase matching, includes nonlinear

Cerenkov diffraction

(NCD), nonlinear Raman–Nath diffraction (NRND), and

nonlinear Bragg diffraction (NBD). For NCD, the longi-

tudinal phase matching (LPM) is satisfied when the longi-

tudinal direction is parallel to the incident fundamental

laser beam. This phase matching can be achieved by the

addition of integer multiples of the incident wave vector

or the combination of the incident wave vector and recip-

rocal vectors. In the case of NRND, the transverse

(perpendicular to the incident fundamental laser beam)

phase matching (TPM) has to be satisfied. This can be

achieved by the combination of the reciprocal vectors. How-

ever, for the NBD process to occur, both LPM and TPM

need to be satisfied. In the past twenty years, second-

harmonic generation (SHG) via various nonlinear diffrac-

tions in 1D and 2D NPCs had been the major focus

[7–13]

Although high-order harmonics (HH) are very important

to the field of nonlinear optics, until recently, publications

on HH generation using NPCs have been almost nonexist-

ent. Recently, there have been several significant efforts to

generate third harmonics in periodic, short-range ordered

or radially poled NPCs, NPC waveguide and random quad-

ratic media by NCD and NRND

[14–18]

. Also, high efficiency

quasi-phase-matched harmonic generation from the 2nd to

8th order have been observed within a single LiNbO

(LN)

NPC

[19]

. However, fourth-harmonic generation (FHG) via

nonlinear diffraction is rarely reported. The advantage of

using a 2D fractal superlattice is that it may allow the

freedom of optimization of many parameters such as input

wavelength, harmonic order, angle, and efficiency. In this

Letter, second, third, and especially multiple fourth har-

monics are achieved by nonlinear diffractions in an LN

NPC with Sierpinski fractal superlattices under femtosec-

ond pulses.

In our experiment, a fourth-order Sierpinski fractal super-

lattice as a unit is adopted in z-cut LN NPC

[20]

, where the

second order is square and the other three orders are circles.

On the basis of the fractal structure, the ratio of the distan-

ces between the two neighboring maximum circles and the

two neighboring minimum circles is 27. This unit is then

repeated in the xoy plane. The interval between the

repeated units is exactly the distance between the two

neighboring minimum circles, i.e., 13.64 μm. The second-

order susceptibilities χ

ð2Þ

in the circular and square regions

are reversed by an external high-voltage electric field. The

length, width, and thickness of the sample are 8, 8, and

0.4 mm, respectively. The diameters of the first-, third-,

and fourth-order circles are 110, 12, and 5 μm, respectively,

and the side length of the second-order square is 37 μm.

Based on the formation of the Sierpinski superlattices,

the magnitude of the basic reciprocal vector G

⇀

is set to

be G

¼ 2π∕13.64, as seen in Fig. 1. Multiple reciprocal vec-

tors distribute in the xoy plane.

The input fundamental 100 fs laser pulses with 2 μm

central wavelength are generated from an optical para-

metric amplifier (OPA, Spectra-Physics) pumped by a

home built 0.5 kHz Ti:sapphire laser operating at

780 nm wavelength with an 80 fs pulse width. The input

fundamental wavelength is linearly (vertically) polarized

with a pulse energy of approximately 30 μJ. The laser

pulses are incident along the z axis of the crystal so that

they are perpendicular to the reciprocal vectors of

COL 15(5), 051901(2017) CHINESE OPTICS LETTERS May 10, 2017

下载后可阅读完整内容，剩余4页未读，立即下载

weixin_38646706

粉丝: 4
资源: 1005

二维LiNbO3非线性光子晶体中的四次谐波产生

High-power ultraviolet 278nm laser from fourth-harmonic generation of a Nd；YAG laser in CsB3O5

The Quenching Phenomena for Fourth-order Nonlinear Parabolic Equationos

Saturation behavior of a one-pump fiber optical parametric amplifier in the presence of the fourth-order dispersion coefficient and dispersion fluctuation

ignite-fourth-challenge-solid

fourth-grade-word-problems

DOA estimation based on fourth-order cumulants in the presence of sensor gain-phase errors

Project-The-Fourth-Pneumonia-X-Ray

fourth-milestone-project

The-fourth-assignemnt

fourth-checkpoint

最新资源