STUDY OF NEGATIVE REFRACTIVE INDEX IN Rb FOUR-LEVEL N-TYPE ATOMIC GAS MEDIUM

In this work, we study the generation of a negative refractive index based on electromagnetically induced transparency (EIT) in a Rb four-level N-type atomic gas medium. We derive analytic expressions for the relative permittivity and relative permeability of the medium according to the parameters of the probe, pump, and signal laser fields. We then investigate the variation of the real parts of the relative permittivity and relative permeability with respect to the intensity and frequency of the pump and signal laser fields. In the presence of the pump laser beam, the medium becomes transparent to the probe laser beam even in the resonant region. At the same time, the real parts of the relative permittivity and relative permeability are simultaneously negative (i.e., the medium exhibits a negative refractive index) in the EIT spectral domain. In the presence of the signal laser beam, the EIT effect occurs over two different frequency domains of the probe beam, so a negative refractive index is also generated in these two frequency domains. The investigation of the real parts of the relative permittivity and relative permeability with intensity and frequency of the pump and signal laser fields allowed us to find the laser parameters for the appearance of the negative refractive index, which can be useful for experimental observations

Controllable Optical Properties of Multiple Electromagnetically Induced Transparency in Gaseous Atomic Media

The advent of electromagnetically induced transparency (EIT) offered a new coherent material with exotic and controllable optical properties. Although, studies on single-EIT are described in detail for single-EIT, however, extension from single- to multi- EIT is currently of current interest due to it gains advantages in multi-channel optical communication, waveguides for optical signal processing and multi-channel quantum information processing. In this work, we review recent research works concerning multi-EIT and some related applications, as controlling group velocity of light, giant Kerr nonlinearity, optical bistability. A special attention of the review also gives for analytical interpretations of EIT spectrum, its dispersion and related applications such as EIT enhanced Kerr nonlinearity and optical bistability to give physics insight. From experimental point of view, a latest development for measuring multi-EIT spectrum and its dispersion in hot medium is presented and compared to theoretical analytical representations

EIT enhanced self-Kerr nonlinearity in the three-level lambda system under Doppler broadening

Using density-matrix theory, an analytical expression of the self-Kerr nonlinear coefficient of a three-level lambda EIT medium for a weak probe light is derived. Influences of the coupling light and Doppler broadening on the self-Kerr coefficient are investigated and compared to experimental observation with a good agreement. The self-Kerr nonlinearity is basically modified and greatly enhanced in the spectral region corresponding to EIT transparent window. Furthermore, sign, slope, and magnitude of the self-Kerr coefficient can be controlled with frequency and intensity of the coupling light and temperature. Such controllable Kerr nonlinearity can find interesting applications in optoelectronic devices working with low-light intensity

A Comparative Study of Optical Bistability in Three-Level EIT Configurations

We present a comparative study of optical bistability (OB) in three-level atomic configurations, including $\Lambda$-, cascade-, and V- types under the conditions of electromagnetically induced transparency (EIT). In the steady regime, the input-output intensity relations for the OB in each configuration have been derived in analytical form. The model allows one to construct a clear picture on how the threshold intensity, and other characteristics of the OB are continuously modified with respects to controllable parameters of the laser fields, cooperation parameter, and other physical parameters of atomic system. The results showed that the threshold intensity of OB in $\Lambda$-type system is much less than the other ones and the threshold intensity of OB in V-type system is the largest one. The analytical result is convenient to choose excitation configuration for experimental observations and related applications in photonic devices

Simultaneously induced mutations in eIF4E genes by CRISPR/Cas9 enhance PVY resistance in tobacco

Tobacco is an important commercial crop and a rich source of alkaloids for pharmaceutical and agricultural applications. However, its yield can be reduced by up to 70% due to virus infections, especially by a potyvirus Potato virus Y (PVY). The replication of PVY relies on host factors, and eukaryotic translation initiation factor 4Es (eIF4Es) have already been identified as recessive resistance genes against potyviruses in many plant species. To investigate the molecular basis of PVY resistance in the widely cultivated allotetraploid tobacco variety K326, we developed a dual guide RNA CRISPR/Cas9 system for combinatorial gene editing of two clades, eIF4E1 (eIF4E1-S and eIF4E1-T) and eIF4E2 (eIF4E2-S and eIF4E2-T) in the eIF4E gene family comprising six members in tobacco. We screened for CRISPR/Cas9-induced mutations by heteroduplex analysis and Sanger sequencing, and monitored PVY(O) accumulation in virus challenged regenerated plants by DAS-ELISA both in T0 and T1 generations. We found that all T0 lines carrying targeted mutations in the eIF4E1-S gene displayed enhanced resistance to PVY(O) confirming previous reports. More importantly, our combinatorial approach revealed that eIF4E1-S is necessary but not sufficient for complete PVY resistance. Only the quadruple mutants harboring loss-of-function mutations in eIF4E1-S, eIF4E1-T, eIF4E2-S and eIF4E2-T showed heritable high-level resistance to PVY(O) in tobacco. Our work highlights the importance of understanding host factor redundancy in virus replication and provides a roadmap to generate virus resistance by combinatorial CRISPR/Cas9-mediated editing in non-model crop plants with complex genomes

Role of incoherent pumping field on control of optical bistability in a closed three-level ladder atomic system

In this paper, we analyze the role of incoherent pumping field on the control of optical bistability (OB) via the spontaneously generated coherence (SGC) and relative phase between laser fields in a closed three-level ladder-type atomic system. It is shown that in the presence of incoherent pumping field, the influences of the SGC and the relative phase of the OB behavior become more effective. Simultaneously, the threshold intensity and width of the OB reduce significantly when the incoherent pumping rate increases

Controlling negative refractive index of degenerated three-level

We have achieved the negative refractive index for the probe light in a degenerated three-level $$\Lambda$$-type atomic medium under electromagnetically induced transparency. The width of the frequency band of the negative refractive index can be changed by adjusting the coupling light intensity, while the position of the frequency band of the negative refractive index can be shifted to low or high frequency region by varying the coupling light frequency or the external magnetic field. Furthermore, the positive refractive index for a given probe frequency can be converted to the negative refractive index and vice versa by adjusting the strength or the sign of the magnetic field. This means that we can use the external magnetic field as a “knob” to control the sign of the refractive index of the material which can obtain the desired material with positive or negative index

PHÂN TÍCH SỰ TĂNG CƯỜNG VÀ ĐIỀU KHIỂN HỆ SỐ PHI TUYẾN KERR CỦA MÔI TRƯỜNG NGUYÊN TỬ BA MỨC CHỮ V MỞ RỘNG KHÔNG ĐỒNG NHẤT

The analytical expression for the self-Kerr nonlinear coefficient in a three-level V-type atomic medium is found in the presence of the Doppler effect. Based on the analytical results, we have analyzed the enhancement and control of the Kerr nonlinear coefficient under the condition of electromagnetically induced transparency. It is shown that the Kerr nonlinear coefficient is significantly enhanced around the resonant frequency of both the probe and coupling fields. Simultaneously, the magnitude and sign of the Kerr nonlinear coefficient are controlled with respect to the intensity and frequency of the coupling laser field. The amplitude of the Kerr nonlinear coefficient decreases remarkably as temperature increases (i.e., the Doppler width increases). The analytical model can find potential applications in photonic devices and can explain experimental observations of the Kerr nonlinear coefficient at different temperatures.Biểu thức giải tích của hệ số phi tuyến Kerr trong môi trường nguyên tử ba mức chữ V đã được dẫn ra trong sự có mặt của hiệu ứng Doppler. Dựa vào các kết quả giải tích, chúng tôi đã phân tích được sự tăng cường và điều khiển hệ số phi tuyến Kerr dưới điều kiện trong suốt cảm ứng điện từ. Nó cho thấy rằng, hệ số phi tuyến Kerr được tăng cường đáng kể xung quanh tần số cộng hưởng của cả chùm dò và chùm liên kết. Đồng thời, biên độ và dấu của hệ số phi tuyến Kerr cũng được điều khiển theo cường độ và tần số của laser liên kết. Biên độ của hệ số phi tuyến Kerr bị giảm đáng kể khi nhiệt độ của môi trường nguyên tử tăng lên (hay độ rộng Doppler tăng). Mô hình giải tích này có thể tìm được các ứng dụng hữu ích trong các thiết bị photonic hoặc để giải thích các kết quả quan sát thực nghiệm hệ số phi tuyến Kerr dưới các nhiệt độ khác nhau

Optical Bistability in a Controllable Giant Self-Kerr Nonlinear Gaseous Medium under Electromagnetically Induced Transparency and Doppler Broadening

We study optical bistability (OB) in a controllable giant self-Kerr nonlinear atomic gaseous medium placed in a unidirectional ring cavity. The medium is coherently excited by strong controlling field and a weak probe laser field under electromagnetically induced transparency (EIT) and Doppler broadening. In a weak field limit of the probe light, an analytic OB equation for the probe light field is derived as an analytic function of parameters of the controlling field and temperature of the medium. It is shown that OB characters can be manipulated with the parameters due to the controllable properties of the self-Kerr nonlinearity. Furthermore, enhancement of the Kerr nonlinearity reduces the switching intensity threshold and width of the OB

The influence of spontaneously generated coherence and phase of laser fields on optical bistability in a three-level atomic medium: an analytical approach

The influence of spontaneously generated coherence and relative phase of laser fields on optical bistability in a three-level atomic medium under electromagnetically induced transparency was studied by using a density matrix theory. An input-output intensity relation of a probe laser field is derived as an analytical function of parameters of a controlling light field, the relative phase, and the spontaneously generated coherence. This function can be fitted with experimental values to be a semi-empirical model which is helpful for finding related applications. It is shown that thresholds and width of the optical bistability hysteresis loop can be manipulated with the controllable parameters. On the other hand, the influence of population relaxation between two ground hyperfine levels on the optical bistability behavior is significant for small coupling field intensity