基于有机吡啶盐晶体的太赫兹频率上转换探测

Terahertz wave up-conversion detection based on organic nonlinear optical crystals

利用激光泵浦国产有机吡啶盐4-(4-二甲基氨基苯乙烯基)甲基吡啶对甲基苯磺酸盐(4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate,DAST)晶体,通过非线性频率上转换方法实现了室温运转的高灵敏、快响应、宽频段太赫兹探测.高效生成了近红外上转换光,采集到其脉冲包络和光谱,获得了ns量级的时间分辨率,并换算太赫兹波的频率,实现了对太赫兹信息的全面表征.与商用高莱探测器相比,上转换方法在19 THz频点的探测灵敏度高4个数量级;在可探测频率3.15—29.82 THz范围内,响应度普遍高2—3个数量级.结果表明:室温下的光泵频率上转换探测方法在时间分辨率和响应度方面远优于传统的热探测器,极大地提高了差频有源太赫兹系统的动态范围,使差频源在太赫兹波谱分析和成像等领域具有更大的应用潜力.

Laser pumped terahertz(THz)wave up-conversion detection with high sensitivity,fast responsivity and wide frequency band is achieved at room temperature,based on home-made organic nonlinear crystals 4-N,Ndimethylamino-4′-N′-methyl-stilbazolium tosylate(DAST).Green laser pulses pumped KTiOPO4 optical parametric oscillators are utilized as the sources of dual-wavelength near-infrared(NIR)beams(1.3–1.6μm,for THz-wave difference frequency generation(DFG))and a single NIR beam(1.2–1.4μm,for up-conversion detection).The nonlinear medium for both THz-DFG and detection is DAST(grown by CETC-46).A nanosecond-time-resolved THz pulse is obtained with an InGaAs p-i-n photo-diode.The spectrum of the upconverted NIR light is acquired,which allows us to measure the THz frequency indirectly.The sensitivity(also at room temperature)is 4 orders better at 19 THz than the sensitivity of a commercial thermal detector(Golay Cell).The wide frequency band operation is realized with different sets of band-pass filters,which cover the entire range from 3.15 to 29.82 THz except 8.4 THz of the strong absorption peak of DAST.The dynamic range of a THz source based on DFG can be commonly improved by 2–3 orders,by changing the traditional thermal detector with the up-conversion detection.The presented technology can promote the applications of DFG THz source in the fields of high-resolution spectroscopy and imaging.