Terahertz Computed Tomorgraphy with a Quantum Cascade Laser and a Quantum-well Photodetector

Tao Zhou,Li Gu,Zhi-Yong Tan,Jun Cheng Cao 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.2

In this letter, a terahertz (THz) tomography system based on a quantum cascade laser (QCL)and a quantum-well photodetector (QWP) is demonstrated. The QCL provides a relatively high power (a few microwatts) in a continuous-wave mode at 3.9 THz as a light source, and the QWP provides a narrow response range from 3 to 7 THz with a calibrated peak response of 0.5 A/W under background-limited performance. We employ the widely-used filtered back projection (FBP)and algebraic reconstruction algorithms for terahertz tomography technology. The reconstructed cross-sectional image of a sample has successfully revealed the internal and the external structures with a resolution of around 1.5 mm. This experiment demonstrates that the terahertz QCL and the photodetector are potentially useful for terahertz tomography applications.

중적외선 양자 다단계 레이저의 고효율 빔 결합 방법에 대한 시뮬레이션 및 광특성 비교

곽지윤,박영호,조수형 한국물리학회 2021 새물리 Vol.71 No.3

Recently, the quantum cascade laser (QCL) has been spotlighted as a next-generation light source in the mid-infrared region because of its increase in optical power due to the development of manufacturing technology. However, the optical power of a single QCL is limited by the self-heating effect. Therefore, high-efficiency beam combination technology is essential to achieve a high-power mid-IR laser. In this paper, we demonstrate a simple and effective beam combination method that can be used for QCLs in the 3.85 – 4.15 m wavelength region. We achieved a high 89.0% efficiency by combining three QCLs using flat mirrors. In addition, we adjusted the divergence angles of the fast axis and the slow axis equally for easy application in various wavelength regions. 최근 양자 다단계 레이저는 제작 기술이 발달함에 따라 광출력이 증가하여 중적외선 영역에서차세대 레이저로 각광 받고 있다. 그러나 단일 양자 다단계 레이저(Quantum Cascade Laser, QCL)의출력은 자기 가열효과에 의해 제한된다. 따라서 고출력 중적외선 레이저를 구현하기 위해서는 빔 결합기술이 필수적이며, 다양한 분야에 적용하기 위해서는 쉽고 간단한 빔 결합 방식이 고려 되어야한다. 본 논문은 3.85 – 4.15 m 파장 대역을 갖는 QCL의 간단하고 효율적인 빔결합 방식에 대하여보고한다. 평면 거울을 이용하여 3개의 QCL을 빔 결합한 결과, 89.0%의 높은 결합 효율을 달성하였으며, 추가적으로 다양한 분야에 쉽게 적용하기 위하여 빠른 축과 느린 축의 발산각을 동일하게 조절하였다.

Terahertz generation in quantum cascade structures by two-color deriving fields: An approach to reach inversion population via optical pumping

Yousefvand Hossein Reza 한국물리학회 2022 Current Applied Physics Vol.39 No.-

In this paper, a quantum cascade laser (QCL) design is proposed based on GaAs/AlGaAs material system, which simultaneously operates at three widely separated wavelengths (λ1 = 11.1 μm, λ2 = 14.1 μm and λTHz = 60 μm). In the design, all the wavelength radiations are achieved by the engineering of the electronic spectrum via the quantum-well widths and the applied electric field in a single active region within a same waveguide. The midinfrared (mid-IR) wavelengths are obtained by adoption a dual-upper-state active region, and the proposed design aims to use both the mid-IR radiations as the coherent deriving fields to populate the upper THz lasing state to aid the THz-laser population inversion via optical pumping instead of direct electrical injection. A detailed analysis of electronic transport in the structure is carried out using a multi-level rate-equation model. The results show that the proposed structure offers an alternative approach to room temperature THz generation in QCLs.

Spectral Research on an AlGaAs Epitaxial Material for a Terahertz Quantum-cascade Laser

Zhi-Yong Tan,Jun-Cheng Cao 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.8

The spectral properties of a series of AlGaAs epitaxial films were studied by using a Fourier transform infrared spectrometer with an 80-degree grazing incidence reflection unit. The AlAslike transversal optical phonon was obviously observed in the spectra, but the longitudinal optical phonon was obscured in the transmission spectra. The variation curves for the transversal optical phonon energy were acquired from the two kinds of spectra and were compared with each other and with the early results. A comparison of the results show that the grazing incidence reflection spectrum is better in reflecting the AlAs-like phonon energy of an AlGaAs epitaxial film and could be a supplementary means in the characterization of the material for a terahertz quantum-cascade laser.

계단형태의 활성영역을 가진 고출력 양자폭포레이저 특성 연구

안병민,신재철,이요한 한국물리학회 2016 New Physics: Sae Mulli Vol.66 No.4

Conventional quantum cascade lasers (QCLs) are composed of a superlattice structure with identical compositions of quantum wells and barriers. In this structure, the energy difference between the upper laser state and the upper energy states leads to a significant leakage current from the upper laser state to the continuum band at room temperature. As a result, the operating characteristics ($i.e.$, T$_{0}$ and T$_{1}$) of QCLs at roon temperature are poor. In order to suppress carrier leakage in the active region, we suggest a QCL structure employing a tapered-active region (TA). Importantly, the alloy composition of the quantum wells and barriers are varied in this structure. In order to compare the operating characteristics of conventional QCL’s at room temperature with those of TA QCLs, we have examined the leakage current density at various temperatures by using a K$\cdot$P simulation. A significant reduction in the carrier leakage is found for the TA QCL structure. The reduction in the carrier leakage may improve the output power and the wallplug efficiency of the QCL during room-temperature, continuous-wave 기존의 양자폭포레이저는 동일한 조성비의 양자우물과 장벽이 연속적으로 적층된 구조 (초격자 구조)를 가지고 있다. 이러한 구조에서는 상위 에너지 준위간의 작은 에너지 차로 인해 상온에서 다량의 누설전류가 발생하므로 양자폭포레이저의 상온동작특성이 크게 떨어지게 된다. 본 논문에서는 상온동작 시 누설전류를 억제하기 위하여 양자우물과 장벽의 조성비를 변화하여 계단형태의 활성영역을 가지는 양자폭포레이저 구조를 제안하였다. 기존의 양자폭포레이저와 계단형태의 활성영역을 가진 양자폭포레이저의 상온동작특성에 대해 비교하기 위해 K$\cdot$P 시뮬레이션을 통하여 온도에 따른 누설전류 및 이를 고려한 문턱전류밀도에 대하여 살펴보았다. 계단형태의 활성영역을 가진 구조를 통한 전체 문턱전류밀도 대비 누설전류밀도의 감소는 상온 연속동작 시 양자폭포레이저의 광출력(output power) 및 월플러그 효율(wall-plug efficiency) 특성을 크게 향상 시킬 수 있다.

Dephasing Effect on the Carrier-light Interaction in Terahertz Quantum Cascade Lasers

Feng Wang,Xu Guang Guo,Jun Cheng Cao 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.41

We study the dephasing effect on the carrier-light interaction in terahertz quantum cascade lasers by using a rate-equation method including the optical field. The time evolution of the gain coefficient and the stimulated radiation rate are shown. We theoretically provide an ultrafast microscopic process for the conversion of a working terahertz quantum cascade laser from an unsaturated to a saturated state.

중적외선 영역의 양자 폭포 레이저 흡수 분광법을 이용한 황산화물 농도 측정에 관한 연구

박지연(Jiyeon Park),맹새롬(Saerom Maeng),소성현(Sunghyun So),유미연(Miyeon Yoo),류창국(Changkook Ryu),이창엽(Changyeop Lee) 한국에너지기후변화학회 2018 한국에너지기후변화학회 학술대회 Vol.2018 No.11

Threshold Current Increase in GaAs/AlGaAs Quantum Cascade Lasers due to the Thickness Variation

한일기,Jeong, Jin-Wook,송진동,JungIlLee 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.4

GaAs/AlGaAs quantum cascade laser (QCL) epi-structures were grown and lased successfully at 77 K. The thickness variation during the growth sequence was measured by analyzing the transmission electron microscope pictures. The thickness of the epi-layer decreased by up to 80 90 % of its expected value. At least three times higher threshold current and shorter lasing wavelength, compared to the reference QCL, were shown. The decrease in the growth rate during the growth sequence is thought to be a possible reason for such a high threshold current and short lasing wavelength.

InGaAs/InAlAs Quantum Cascade Lasers Grown by using Metal-organic Vapor-phase Epitaxy

Dong Hak Kim,Hae Yong Jeong,Young Su Choi,Deoksoo Park,Young-Jin Jeon,Dong-Hwan Jun 한국진공학회(ASCT) 2017 Applied Science and Convergence Technology Vol.26 No.5

In this paper, InP-based InGaAs/InAlAs quantum cascade lasers(QCLs) providing nearly zero emission wavelength mismatch between the measured emission wavelength and the designed transition wavelength of QCLs is presented. The zero emission wavelength mismatch of QCLs influenced by both the accurate compositions and thicknesses of the low-pressure metal-organic vapor-phase epitaxy(MOVPE) grown InGaAs and InAlAs layers throughout the core and the abrupt composition transitions between InGaAs and InAlAs layers. The abrupt interfaces between InGaAs and InAlAs layers have been achieved throughout the core structure by means of controlling individually purged vent/run valves of a closed coupled showerhead reactor. In addition, maintaining substrate temperature constant during InGaAs/InAlAs core growth was a partial factor of uniformity improvement of QCLs. These approaches for reducing the possible discrepancies between the designed and MOVPE grown epitaxial structures could lead to improvement of QCL performance.

양자 폭포 레이저 흡수 분광법을 이용한 다중 선강도를 갖는 NO & NO₂ 가스 농도 계측에 관한 연구

맹새롬(Saerom Maeng),소성현(Sunghyun So),유미연(Miyeon Yoo),김대해(Daehae Kim),황정호(Jungho Hwang),이창엽(Changyeop Lee) 한국에너지기후변화학회 2018 에너지기후변화학회지 Vol.13 No.1

As the interest in ultrafine particle increases, researches on the mechanism of the secondary fine particle, which is generated by chemical reaction with other materials in the air, are active. Most of secondary fine particles are produced by the main generation mechanism with nitrogen oxides (NOx, NO & NO₂). The NOx is generated by energy and power plant systems in our surrounding such as vehicle, exhaust, power plant, and incineration plant, etc.. Normally, NOx is measured by the chemiluminescent method specified by clean air conservation act. However, this method can measure not each molecule such as NO, NO₂ but total NOx only. Therefore, for analyzing reaction accurately, both NO and NO₂ must be analyzed in real time, and the absence of such technology is the one of the reasons that has a limitation of the secondary fine particle generation mechanism analysis. In this paper, NO and NO₂ gas concentrations have been measured separately with multi-line strength absorptions using quantum cascade laser (QCL) in the mid-infrared region. At this time, The center wavelengths of the lasers used are 1851 cm<SUP>-1</SUP>(NO gas) and 1612 cm-1 (NO₂ gas).