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A novel method of evaluating large mode area fiber design by brightness factor

Zhang Hai-Tao, Chen Dan, Ren Hai-Cui, Yan Ping, Gong Ma-Li Citation:Chin. Phys. B , 2015, 24(2): 024207. doi: 10.1088/1674-1056/24/2/024207

Journal homepage: http://cpb.iphy.ac.cn; http://iopscience.iop.org/cpb

What follows is a list of articles you may be interested in

Theoretical analysis of the mode coupling induced by heat of large-pitch micro-structured fibers

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Influence of mode competition on beam quality of fiber amplifier

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Ma Peng-Fei, Zhou Pu, Ma Yan-Xing, Su Rong-Tao, Liu Ze-Jin Chin. Phys. B , 2012, 21(9): 094206. doi: 10.1088/1674-1056/21/9/094206 ------

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Phys. B Vol. 24, No. 2 (2015) 024207

A novel method of evaluating large mode area fiber design by brightness factor∗

Zhang Hai-Tao(张海涛)a)†, Chen Dan(陈 丹)b), Ren Hai-Cui(任海翠)a), Yan Ping(闫 平)a), and Gong Ma-Li(巩马理)a)‡

a)Center for Photonics and Electronics, State Key Laboratory of Tribology, Department of Precision Instruments, Tsinghua University, Beijing 100084, China b)Southwest Institute of Technical Physics, 610041, China

(Received 3 July 2014; revised manuscript received 16 August 2014; published online 10 December 2014)

A novel evaluation term and a more reasonable criterion, which is described by a new parameter of brightness factor for active large mode area fiber design, are presented. The brightness factor evaluation method is based on the transverse mode competition mechanism in fiber lasers and amplifiers. The brightness factor can be seen as a description of fiber general property since it can represent the output laser brightness of the fiber laser system and because of its ability to resist the nonlinear effect. A core-doped active large pitch fiber with a core diameter of 190 µm and a mode-field diameter of 180 µm is designed by this method, and the designed fiber allows effective single-mode operation.

Keywords: brightness factor, large pitch fiber, mode competition PACS: 42.55.–f, 42.55.Wd DOI: 10.1088/1674-1056/24/2/024207

1. Introduction yond 50 µm) active fibers have been developed to provide Fiber lasers with high power, excellent beam quality, and mode scaling, such as semi-guiding high-aspect-ratio-core [8] [9] high efficiency are increasingly being developed for many ap- (SHARC) fibers, gain-guided, index-antiguided fibers, [10] plications and in many areas such as industry, medicine, com- and photonic crystal fibers (PCFs). In theory, the SHARC munication, military, and research. The average output power structure implies nearly unlimited effective MFD scalability has been scaled beyond the ten kilowatt level, maintaining a but it has a multimode beam quality in the slow-axis direc- near-diffraction-limited beam quality.[1] However, scaling the tion. In addition, the gain-guided, index-antiguided fiber is pulse energy and peak power of fiber lasers is more challeng- quite challenging to obtain high pump efficiency due to the ing. The peak power and energy level are limited by nonlin- leaky cladding. Among them, the active PCF, especially the ear effects, such as stimulated Raman scattering (SRS) and large pitch fiber (LPF) structure with pitches 10 times larger stimulated Brillouin scattering (SBS) due to the high optical than the wavelength, seems to be one of the most promis- [10–13] intensity and long interaction length in the fiber.[2,3] Scaling ing approaches for a core diameter beyond 100 µm. In to larger effective mode-field-diameter (MFD) helps reduce LPF mode area scaling studies, the fiber designs are usually [14,15] the optical density and the effective working length of the guided in terms of transversal mode discrimination, i.e., fiber with the same ytterbium or other rare-earth dopants be- differential propagation losses between modes, especially the cause raising the core size leads to the increase of the core- mode discrimination of the fundamental mode (FM) and the to-cladding ratio and the pumping absorption efficiency in- first HOM. creases. For step-index fibers, prominent techniques for ef- However, in fiber laser system we are more concerned fective single-mode operations include matched excitation by with the laser performance of the VLMA-active LPF in the particularly ion-doping,[4] and higher-order mode (HOM) dis- high power dynamic mechanism than in a simple passive crimination by bending[5] or by filtering through high loss waveguide mechanism. Hence, in this paper, we present a waveguide structure, such as a chirally coupled core.[6] How- novel evaluation term and a reasonable criterion for active LPF ever, these methods have limited effective MFD scalability be- designs for laser applications. We define a novel parameter 훾, cause the mode propagation coefficients of the normal step- brightness factor, as the evaluation term. The brightness fac- index fibers with core sizes beyond 50 µm will become too tor is defined as the product of output laser brightness in unit densely packed to discriminate between the fundamental mode pump power and the square of effective MFD (proportional and its nearest neighbors.[7] to mode field area) and it has no dimension. Therefore, the Novel very large mode area (VLMA, core diameter be- brightness factor 훾 allows one to take all factors into consid- ∗Project supported by the National Natural Science Foundation of China (Grant No. 61475081). †Corresponding author. E-mail: [email protected] ‡Corresponding author. E-mail: [email protected] © 2015 Chinese Physical Society and IOP Publishing Ltd http://iopscience.iop.org/cpb http://cpb.iphy.ac.cn 024207-1 Chin. Phys. B Vol. 24, No. 2 (2015) 024207 eration on fiber designs, including the effective MFD, laser ture of an LPF with a fixed core diameter, the normalized hole beam quality, and conversion efficiency of the output beams. size is modified. The mode profiles and the propagation losses A higher value of the brightness factor 훾 of the VLMA fiber due to leakage are calculated by a mode solver based on the laser indicates a higher output laser brightness, and the higher finite element method (FEM). mode area means that it has a higher ability to resist the non- linear effect. In conditions of enlarged MFD, in order to ob- y tain the output beam brightness (relating to the efficiency and beam quality with unit pump power) of the fiber laser with unit power, we need not only investigate the mode discrimination (a) in the propagation process, as shown in Refs. [14] and [15], d but should also study the transverse mode competition along the fiber in the amplification process. The best structure with respect to each core-diameter value is the one in which the o x brightness factor achieves a maximum value. Unlike the op- timization method that is commonly adopted in LPF design, Γ which is to find the maximum loss difference by a fixed FM loss, this optimization method requires the maximum bright- ness factor. The brightness factor can integrate many design z methods, making this method suitable not only for the LPF (b) fiber but also for the design of other fiber structures. y R1 + - R In this paper, we first introduce the calculation of bright- Pp (z) Pp (z) 2 ness factor and present the LPF structure design procedure us- pump pump ing the maximum brightness factor as a criterion. In order to x output compare with the design result of fixed FM loss, the core di- P +(z) - z/ s Ps (z) z/L ameter is selected as 51 µm, which is the same as the value in I fiber lasers z Ref. [14]. We then conduct further design with LPF of larger y core size by the brightness factor method. Finally, as an ex- + - Pp (z) Pp (z) ample of the extension and application of the brightness factor signal evaluation method (BFEM), a Yb-doped LPF with the largest pump pump x output core diameter of 190 µm and an effective MFD of 180 µm is + z/ Ps (z) designed. z/L II fiber amplifiers 2. Brightness factor evaluation method Fig. 1. (color online) The LPF schematic model, showing (a) the cross section of the LPFs, and (b) the laser cavity and the amplifier. As shown in Fig. 1(a), all of the Yb-doped PCFs consid- ered in this paper have two rings of hexagonally arranged air However, in addition to the eigenmode propagation char- holes with the core formed by one missing air-hole because acteristics, we are more concerned with the laser performance this kind of structure can offer the highest mode discrimina- of the active LPF in the high-power dynamic mechanism. The tion between FM and first HOM combined with an FM hav- dynamic mode analysis of the LPF laser utilizes the typical ing a moderate loss of beam quality.[14] The hole-to-hole dis- linear cavity as described schematically in Fig. 1(b). The sig- tance (Γ ) and the normalized hole-diameter (d/Γ ) determine nal powers of each mode and the pump power are given by the the properties of the LPFs, such as propagation loss, single- following space-dependent and time-independent steady-state mode regime, and effective mode area. To optimize the struc- rate equations:[16]

+ − + − [Pp (z) + Pp (z)]σapΓp(x,y) [P (z) + P (z)]σasΓsi(x,y) + ∑ si si N2(x,y,z) hνp i hνs = + − + − , (1) N1(x,y,z) [Pp (z) + Pp (z)]σepΓp(x,y) 1 [P (z) + P (z)]σesΓsi(x,y) + + ∑ si si hνp τ i hνs ± ZZ  dPp (z)   ± ± ± = σepN2(x,y,z) − σapN1(x,y,z) Γp(x,y)dxdy Pp (z) − αpPp (z), (2) dz A 024207-2 Chin. Phys. B Vol. 24, No. 2 (2015) 024207 ± ZZ  dPsi (z) ± ± ± = [σesN2(x,y,z) − σasN1(x,y,z)]Γsi(x,y)dxdy Psi (z) − αsiPsi (z), (3) dz A where τ is the spontaneous lifetime of the upper lasing level; output laser brightness of fiber laser system and its ability to h is the Planck constant; νs and νp are the laser and pump resist nonlinear effect, therefore it can be seen as a description frequencies, respectively; N2 and N1 are the population den- of the fiber’s general properties. For VLMA fibers, the higher sities of the lower and upper lasing levels; N0 = N1 + N2 is the brightness factor 훾 is, the better the properties of the fiber + − the doping concentration distribution; Pp (z) and Pp (z) are the will be. This is a more reasonable criterion for active LPF + pump powers in the +z and −z directions, respectively; Psi (z) designs. − and Psi (z) are the signal powers of the i-th transverse mode By substituting the filling factor and loss of each mode in the +z and −z directions, respectively; σαp (σαs) and σep inside the doped core into the rate equations, we can ob- (σes) are the pump absorption (emission) and signal absorp- tain the mode competition result and power weights. We can tion (emission) cross sections, respectively; αp and αsi are the then calculate conversion efficiency of the output beam by laser and pump loss factors of the i-th mode, respectively; and, η=Ptot/Ppump. The corresponding effective MFD of FM can RR RR 2 1/2 [7] Γp and Γsi are the pump and signal of the i-th mode power fill- be defined as deff = 2 I(x,y)dxdy/(π I (x,y)dxdy) ing factor. and the beam quality factor (M2) can be calculated by the Additional boundaries are needed to solve the coupled method presented in Ref. [18]. Thus, the brightness factor 훾 differential Eqs. (1)–(3), the boundary conditions on both sides of the output beam is obtained. The highest brightness fac- are given by tor is the best output beam property which corresponds to the + − optimal d/Γ . Psi (0) = R1Psi (0), − + P (0) = R2P (0), (4) si si 3. Numerical simulation results and discussion where L is the fiber length; R1 and R2 are the reflectivities d ) of the reflectors at z = 0 and z = L, respectively. Rate equa- As shown in Fig. 1(a), the core diameter ( core can be d = − d tions (1)–(3) along with boundary conditions (4) are iterated obtained by core 2Γ . Thus, when the core diameter out + is fixed, only the optimal d/Γ is needed to determine the best with the value of the output power Psi = (1 − R2)Psi (L) as the convergence criterion. The total average output power structure of the LPF. Using the BFEM presented above, we op- out timize the structures of the LPFs with core diameters varying Ptot = ΣPsi is derived. In the fiber laser system, the brightness of a laser is used from 51 µm to 190 µm. to describe its ability to produce the highest power in the 3.1. Structure optimization of the 51-µm core size LPFs smallest spot and the smallest divergence. The brightness of a low diverging laser source for the circular case is described Firstly, we simulate the mode profiles and the propagation 2 2 2 2 [17] losses of LPFs with a fiber core diameter of 51 µm and various as B = Ptotal/(M λ) = Ppη/(M λ) , where λ is the laser wavelength. For VLMA fibers, the ability to resist nonlinear values of d/Γ (dcore = 2Γ − d). The proportion of the inner effect is another criterion to qualify fiber performance, which cladding diameter to the core diameter maintains 3.15 since is related to the power density. When the laser brightness in the this is a reasonable structure, as presented in Ref. [17]. This unit pump power meets the requirement, the larger the mode inner-cladding size can make sure the small-signal pump ab- area, the stronger the ability to resist nonlinear effect will be. sorption coefficient is larger than 3 dB/m. As shown in Fig.2, With both desirable factors, including high brightness and high we use the design of an LPF with a normalized hole-diameter nonlinear effect resistance, taken into consideration, we pro- of 0.3 to illustrate the eigenmode simulation process and the pose a new parameter of brightness factor 훾 for the character- results obtained by FEM. The loss of FM is 1 dB/m and the ization of laser beams. This is defined as first HOM deformation is 81 dB/m, which are in accordance with those in Ref. [14], showing the correctness of the method 2 2 2 훾 = deffη/(M λ) , (5) we used. In the case that the core diameter and the other pa- where η/(M2λ)2 denotes the output laser brightness in unit rameters are fixed, we consider a 1.2-m-long Yb-doped fiber pump power. Brightness factor has instructive meaning in two laser which is pumped at 975 nm with 200-W forward pump aspects. (i) When the MFD of FM is fixed, the higher the power. The laser wavelength (λs) is 1040 nm. Γ or LPFs with output laser brightness in unit pump power is, the higher the a core diameter of 51 µm, the output beam effective MFD and pump conversion efficiency and the better focus intensity of the M2 of LPF lasers versus the values of d/Γ are shown in the fiber laser will be. (ii) When the laser brightness is fixed, Fig. 3(a). With the increase of d/Γ , the MFD of the output the larger the MFD of FM is, the smaller the power density beam declines until d/Γ ≥ 0.39. The d/Γ = 0.39 is an inflec- will be, which can effectively resist nonlinear effect for high tion point. The variation trend of the beam quality factor is peak power pulses. The brightness factor can represent the similar to that in the case of the effective MFD. 024207-3 Chin. Phys. B Vol. 24, No. 2 (2015) 024207

9 mm 30 mm

51 mm

88.3% (1.0 dB/m) 31.5% (82.0 dB/m)

15.3% (95.6 dB/m) 14.4% (490.2 dB/m) 10.4% (257.9 dB/m)

Fig. 2. (color online) Calculated modal intensity profiles of an LPF (d/Γ = 0.3, dcore = 51 µm;), the corresponding overlap of the mode field with the core area and the propagation losses (ordered by decreasing doping overlap).

2.2 m 70 three parameters, is used to find out the optimal d/Γ . The first ) m (a) 2 HOM discrimination and the brightness factor 훾 of unit spec- M 60 1.8 tral width versus the d/Γ are shown in Fig.4. The brightness

50 factor 훾 reaches its highest value when d/Γ = 0.39 where the 1.4 first HOM discrimination is 21 dB/m. Our study indicates that 40 the optimal d/Γ for LPFs with the core diameter of 51 µm is 1.0 0.39, which can reduce the loss of FM to 0.08 dB/m while re- 30 maining near diffraction-limited beam quality, differing from Beam qualityBeam ( factor Effectivediameter/ mode 20 0.6 0.20 0.30 0.40 0.50 the result of Ref. [14] in the respect that the optimal d/Γ is d/Γ 0.3 when the loss of FM is 1 dB/m and the first HOM discrim-

-1 ination is 81 dB/m for the same core size fiber. Thus, it can be 25 m S (b) 80 seen that the LPF structure optimized by BFEM has a smaller 20 mode loss, which can improve the conversion efficiency and 60 the laser brightness. 15

10 40 -1 300 1200

m 5 20 S

0 0 efficiency/% Conversion 200 800

Propagation loss of PropagationFM/dB loss of 0.20 0.30 0.40 0.50 d/Γ γ Fig. 3. (color online) (a) Effective MFD and M2 and (b) propagation 100 loss and optical–optical conversion efficiency versus d/Γ of the FM 400 with dcore = 51 µm.

2 As presented in Fig.3, the optimal effective MFD, M of 0 0 the output laser and the conversion efficiency correspond to 0.20 0.30 0.40 0.50 different values of optimal d/Γ . As a result, each single pa- discrimination/dB HOM First d/Γ rameter cannot reveal the property of the LPF laser accurately. Fig. 4. (color online) The firt HOM discrimination and the brightness Therefore, the brightness factor 훾 , which synthesizes all the factor 훾 versus d/Γ with dcore = 51 µm. 024207-4 Chin. Phys. B Vol. 24, No. 2 (2015) 024207

3.2. Structure optimization of LPFs with large core diam- As shown in Fig.6, we further design the LPFs in terms eters of mode discrimination with a fixed FM loss of 1 dB/m, as pre- According to the BFEM presented above, in the simula- sented in Ref. [14], and make a comparison of laser brightness tions below we optimize the structures of the LPFs with core in unit pump power between these two design criteria. We diameters varying from 51 µm to 190 µm. The inner guid- can see that the LPF with a core diameter less than 190 µm ing structure (the pitch and the d/Γ ) is modified, and the can obtain higher laser brightness when evaluated by using Yb-doped area of each fiber is equal to the mode-field-area. the brightness factor. This is because the FM loss of the LPF We use the fiber amplifier system since the VLMA fibers are designed by the BFEM is less than 1 dB/m, thus improving generally applied to the amplifier system. The optimal d/Γ the conversion efficiency. In addition, the laser beam quality is a little better. The comparison illustrates the advantage of and the FM propagation loss of LPF versus dcore diameter are shown in Fig. 5(a). It can be seen that the larger core diameter the BFEM. The BFEM considers the mode competition which requires a smaller d/Γ to obtain the highest brightness factor, conforms to the actual working mechanisms of the laser and leading to a high leakage of the FM. The FM loss of the 190- amplifier. Improving the fiber laser brightness and improving µm core size LPF is around 1 dB/m, which is a reasonable the ability to resist nonlinear effect are its goals. The BFEM is value for a short high power fiber amplifier. suitable for designing other kinds of large mode area rare-earth doped fibers.

0.42 1.2 -1 m

S 6.0

(a) -1 1.0 1 dB/m of FM loss sr 0.36 S brightness factor evaluation -2 0.8 5.0 cm S Γ 0.30 0.6 d/ kW

4 4.0 0.4 0.24 0.2 3.0 0.18 0 60 100 140 180 Propagation loss of FM/dB of loss Propagation dcore/mm Brightness/10 2.0 60 100 140 180 200 1.45 d ) core/mm (b) 2 M

m Fig. 6. (color online) Comparison of the laser brightness in unit pump m 160 1.35 power between two design criteria.

120 1.25 4. Conclusions

80 1.15 In this paper, a novel evaluation term and a reasonable

Effective MFD/ Effective criterion, which is described by a new parameter of bright-

40 1.05 qualityBeam ( factor ness factor for active large pitch fiber design, are proposed. 60 100 140 180 The BFEM is based on the transverse mode competition in dcore/mm the LPF laser and it synthesizes the effective MFD of FM, Fig. 5. (color online) (a) Optimal d/Γ and the propagation loss and (b) 2 laser beam quality, and conversion efficiency of the output effective MFD and M versus dcore. laser beams. The structures of the LPFs with core diameters To describe the behaviors of all modes in the amplifica- varying from 51 µm to 190 µm are optimized. The LPF opti- tion process, we assume that all of the modes have the same mized by BFEM can ensure that the loss of the FM is less than signal power, which usually represents the case of the worst 1 dB/m. The laser brightness decreases with the fiber core size input beam quality. The signal power of each mode is 10 W due to the rising FM loss. An LPF with very large core size and the forward pump power is 500 W. The output beam prop- (core diameter of up to 190 µm) is designed, allowing for very erties of each amplifier are shown in Fig. 5(b). It is shown that large mode diameter (180 µm) at high average power with near the effective MFD of the output laser beam tends to linearly diffraction-limited beam quality. increase with the augment of the fiber core diameter, directly resulting in the enlargement of the threshold of the nonlinear References effect. The beam quality factor M2 rises slightly due to the [1] Gapontsev V, Fomin V, Ferin A and Abramov M 2010 OSA Technical reduction of d/Γ . A large effective MFD of 180 µm with Digest Series, Washington, DC, paper AWA1 M2 ≈ . [2] Carter A, Samson B, Tankala K, Machewirth D P, Khitrov V, Manyam excellent near diffraction-limited beam quality ( 1 4) is U H, Gonthier F and Seguin F 2005 Boulder Damage Symposium achieved when the core diameter is 190 µm. XXXVI, International Society for Optics and Photonics, p. 561 024207-5 Chin. Phys. B Vol. 24, No. 2 (2015) 024207

[3] Limpert J, Schreiber T, Liem A, Nolte S, Zellmer H, Peschel T, [11] Jansen F, Stutzki F, Liem A, Jauregui C, Limpert J and Tunnermann¨ Guyenot V and Tunnermann¨ A 2005 Opt. Express 11 2982 A 2012 Advanced Solid-State Photonics, Optical Society of America, [4] Bhutta T, Mackenzie J I, Shepherd D P and Beach R J 2002 J. Opt. Soc. AT1A. 4 Am. B 19 1539 [12] Eidam T, Rothhardt J, Stutzki F, Jansen F, Hadrich¨ S, Carstens H, Jau- regui C, Limpert J and Tunnermann¨ A 2011 Opt. Express 19 255 [5] Koplow J P, Kliner D A and Goldberg L 2000 Opt. Lett. 25 442 [13] Stutzki F, Jansen F, Jauregui C, Limpert J and Tunnermann¨ A 2011 [6] Lefrancois S, Liu C, Stock M L, Sosnowski T S, Galvanauskas A and Opt. Lett. 38 97 Wise F W 2013 Opt. Lett. 38 43 [14] Jansen F, Stutzki F, Otto H J, Baumgartl M, Jauregui C, Limpert J and [7] Limpert J, Stutzki F, Jansen F, Otto H J, Eidam T, Jauregui C and Tun- Tunnermann¨ A 2010 Opt. Express 18 26834 nermann A 2012 Light: Science & Applications 1 e8 [15] Dong L, Peng X and Li J 2007 J. Opt. Soc. Am. B 24 1689 [8] Marciante J R, Shkunov V V and Rockwell D A 2012 Opt. Express 20 [16] Gong M, Yuan Y, Li C, Yan P, Zhang H and Liao S 2007 Opt. Express 20238 15 3236 [9] Siegman A E 2007 J. Opt. Soc. Am. B 24 1677 [17] Seurin J F, Xu G, Wang Q, Guo B, Leeuwen R V, Miglo A, Pradhan P, [10] Stutzki F, Jansen F, Liem A, Jauregui C, Limpert J and Tunnermann¨ A Wynn J D, Khalfin V and Ghosh C 2010 Proc. SPIE 7615 1 2012 Opt. Lett. 37 1073 [18] Liao S, Gong M and Zhang H 2009 Laser Physics 19 437

024207-6 Chinese Physics B

Volume 24 Number 2 February 2015

RAPID COMMUNICATION

020505 Onsager principle as a tool for approximation Masao Doi 026103 The influence of ablation products on the ablation resistance of C/C–SiC composites and the growth

mechanism of SiO2 nanowires Li Xian-Hui, Yan Qing-Zhi, Mi Ying-Ying, Han Yong-Jun, Wen Xin and Ge Chang-Chun

GENERAL

020201 Conservation laws of the generalized short pulse equation Zhang Zhi-Yong and Chen Yu-Fu 020202 Self-adjusting entropy-stable scheme for compressible Euler equations Cheng Xiao-Han, Nie Yu-Feng, Feng Jian-Hu, Luo Xiao-Yu and Cai Li 020203 Containment consensus with measurement noises and time-varying communication delays Zhou Feng, Wang Zheng-Jie and Fan Ning-Jun 020204 Response of a Duffing Rayleigh system with a fractional derivative under Gaussian white noise excita- tion Zhang Ran-Ran, Xu Wei, Yang Gui-Dong and Han Qun 020301 From fractional Fourier transformation to quantum mechanical fractional squeezing transformation Lv Cui-Hong, Fan Hong-Yi and Li Dong-Wei 020302 Unified treatment of the bound states of the Schioberg¨ and the Eckart potentials using Feynman path integral approach A. Diaf 020303 Two-electron quantum ring in short pulses Poonam Silotia, Rakesh Kumar Meena and Vinod Prasad 020304 Quantum communication for satellite-to-ground networks with partially entangled states Chen Na, Quan Dong-Xiao, Pei Chang-Xing and Yang-Hong 020305 Time-bin-encoding-based remote states generation of nitrogen-vacancy centers through noisy channels Su Shi-Lei, Chen Li, Guo Qi, Wang Hong-Fu, Zhu Ai-Dong and Zhang Shou 020401 Concrete quantum tunneling spectrum of Schwarzschild black holes Chen Si-Na and Zhang Jing-Yi 020501 Applications of modularized circuit designs in a new hyper-chaotic system circuit implementation Wang Rui, Sun Hui, Wang Jie-Zhi, Wang Lu and Wang Yan-Chao 020502 Complex dynamics analysis of impulsively coupled Duffing oscillators with ring structure Jiang Hai-Bo, Zhang Li-Ping and Yu Jian-Jiang

(Continued on the Bookbinding Inside Back Cover) 020503 Recursion-transform approach to compute the resistance of a resistor network with an arbitrary bound- ary Tan Zhi-Zhong 020504 Antagonistic formation motion of cooperative agents Lu Wan-Ting, Dai Ming-Xiang and Xue Fang-Zheng 020701 Computer simulation of the bombardment of a copper film on graphene with argon clusters A. Y. Galashev and O.R. Rakhmanova 020702 Estimation of spatially distributed processes using mobile sensor networks with missing measurements Jiang Zheng-Xian and Cui Bao-Tong

ATOMIC AND MOLECULAR PHYSICS 023201 Selection of quantum path in high-order harmonics and isolated sub-100 attosecond generation in few- cycle spatially inhomogeneous laser fields Ge Xin-Lei, Du Hui, Wang Qun, Guo Jing and Liu Xue-Shen 023301 Responsive mechanism of 2-(20-hydroxyphenyl)benzoxazole-based two-photon fluorescent probes for zinc and hydroxide ions -Jin, Zhang Qiu-Yue, Ding Hong-Juan, Song Xiu-Neng and Wang Chuan-Kui

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS 024101 Uniform stable conformal convolutional perfectly matched layer for enlarged cell technique conformal finite-difference time-domain method Wang Yue, Wang Jian-Guo and Chen Zai-Gao 024201 Influence of the illumination coherency and illumination aperture on the ptychographic iterative mi- croscopy Liu Cheng, Zhu Jian-Qiang and John Rodenburg 024202 Phase modulation pseudocolor encoding ghost imaging Duan De-Yang, , Du Shao-Jiang and Xia Yun-Jie 024203 Comparison of two absorption imaging methods to detect cold atoms in magnetic trap Wang Yan, Hu Zhao-Hui and Qi Lu 024204 Photon counting statistics of V-type three-level systems: The effects of the field fluctuations Peng Yong-Gang and Zheng Yu-Jun 024205 Position-dependent property of resonant dipole dipole interaction mediated by localized surface plas- mon of an Ag nanosphere Xu Dan, Wang Xiao-Yun, Huang Yong-Gang, Ouyang Shi-Liang, He Hai-Long and He Hao 024206 Frequency-locking and threshold current-lowering effects of a quantum cascade laser and an application in gas detection field Chen Wei-Gen, Wan Fu, Zou Jing-Xin, Gu Zhao-Liang and Zhou Qu 024207 A novel method of evaluating large mode area fiber design by brightness factor Zhang Hai-Tao, Chen Dan, Ren Hai-Cui, Yan Ping and Gong Ma-Li

(Continued on the Bookbinding Inside Back Cover) 024208 Theoretical analysis of the mode coupling induced by heat of large-pitch micro-structured fibers Zhang Hai-Tao, Chen Dan, Hao Jie, Yan Ping and Gong Ma-Li 024209 Optimal oxide-aperture for improving the power conversion efficiency of VCSEL arrays Wang Wen-Juan, Li Chong, Zhou Hong-Yi, Wu Hua, Luan Xin-Xin, Shi Lei and Guo Xia 024210 Power-induced polarization switching and bistability characteristics in 1550-nm VCSELs subjected to orthogonal optical injection Chen Jian-Jun, Xia Guang-Qiong and Wu Zheng-Mao

024211 Theoretical study of the optical gain characteristics of a Ge1−푥Sn푥 alloy for a short-wave infrared laser Zhang Dong-Liang, Cheng Bu-Wen, Xue Chun-Lai, Zhang Xu, Cong Hui, Liu Zhi, Zhang Guang-Ze and Wang Qi-Ming 024212 Very low threshold operation of quantum cascade lasers Yan Fang-Liang, Zhang Jin-Chuan, Yao Dan-Yang, -Qi, Wang Li-Jun, Liu Jun-Qi and Wang Zhan- Guo 024213 A 23.75-GHz frequency comb with two low-finesse filtering cavities in series for high resolution spec- troscopy Hou Lei, Han Hai-Nian, Wang Wei, Zhang Long, Pang Li-Hui, Li De-Hua and Wei Zhi-Yi 024214 Tandem-pumped 1120-nm actively Q-switched fiber laser Wang Jian-Hua, Hu Jin-Meng, Zhang Shi-Qiang, Chen Lu-Lu, Fang Yong, Feng Yan and Li Zhi

024215 1.12-W Q-switched Yb:KGW laser based on transmission-type Bi2Se3 saturable absorber Liu Jing-Hui, Tian Jin-Rong, Hu Meng-Ting, Xu Run-Qin, Dou Zhi-Yuan, Yu Zhen-Hua and Song Yan-Rong 024216 Walk-off reduction, using an external optical plate and Bessel Gaussian interaction Masoume Mansouri, Mohsen Askarbioki, Saeed Ghavami Sabouri and Alireza Khorsandi 024217 Fiber laser pumped burst-mode operated picosecond mid-infrared laser Wei Kai-Hua, Jiang Pei-Pei, Wu Bo, Chen Tao and Shen Yong-Hang 024218 Correction of temperature influence on the wind retrieval from a mobile Rayleigh Doppler lidar Zhao Ruo-Can, Xia Hai-Yun, Dou Xian-Kang, Sun Dong-Song, Han Yu-Li, Shangguan Ming-Jia, Guo Jie and Shu Zhi-Feng 024219 Influences of excitation power and temperature on photoluminescence in phase-separated InGaN quan- tum wells Wang Qiang, Ji Zi-Wu, Wang Fan, Mu Qi, Zheng Yu-Jun, Xu Xian-Gang, Lu¨ Yuan-Jie and Feng Zhi-Hong

024220 ATR-FTIR spectroscopic studies on density changes of fused silica induced by localized CO2 laser treat- ment Zhang Chuan-Chao, Zhang Li-Juan, Liao Wei, Yan Zhong-Hua, Chen Jing, Jiang Yi-Lan, Wang Hai-Jun, Luan Xiao-Yu, Ye Ya-Yun, Zheng Wan-Guo and Yuan Xiao-Dong

024221 First-principles study of structure and nonlinear optical properties of CdHg(SCN)4 crystal Zhang Peng, Kong Chui-Gang, Zheng Chao, Wang Xin-Qiang, Ma Yue, Feng Jin-Bo, Jiao Yu-Qiu and Lu Gui-Wu 024222 Exciplex formation and electroluminescent absorption in ultraviolet organic light-emitting diodes Zhang Qi, Zhang Hao, Zhang Xiao-Wen, Xu Tao and Wei Bin

(Continued on the Bookbinding Inside Back Cover) 024301 Controlling an acoustic wave with a cylindrically-symmetric gradient-index system Zhang Zhe, Li Rui-Qi, Liang Bin, Zou Xin-Ye and Cheng Jian-Chun 024302 Study of acoustic bubble cluster dynamics using a lattice Boltzmann model Mahdi Daemi, Mohammad Taeibi-Rahni and Hamidreza Massah 024303 Homogenization theory for designing graded viscoelastic sonic crystals Qu Zhao-Liang, Ren Chun-Yu, Pei Yong-Mao and Fang Dai-Ning 024304 Pulse decomposition-based analysis of PAT/TAT error caused by negative lobes in limited-view condi- tions Liu Liang-Bing, Tao Chao, Liu Xiao-Jun, Li Xian-Li and Zhang Hai-Tao

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

025101 Short-pulse high-power microwave breakdown at high pressures Zhao Peng-Cheng, Liao Cheng and Feng Ju 025201 Landau damping in a bounded magnetized plasma column H. Zakeri-Khatir and F. M. Aghamir 025202 Relativistic degenerate effects of electrons and positrons on modulational instability of quantum ion acoustic waves in dense plasmas with two polarity ions Liu Tie-Lu, -Liang and Lu Yan-Zhen 025203 Pulsed microwave-driven argon plasma jet with distinctive plume patterns resonantly excited by surface plasmon polaritons Chen Zhao-Quan, Yin Zhi-Xiang, Xia Guang-Qing, Hong Ling-Li, Hu Ye-Lin, Liu Ming-Hai, Hu Xi-Wei and A. A. Kudryavtsev 025204 Experimental and modeling researches of dust particles in the HL-2A tokamak Huang Zhi-Hui, Yan Long-Wen, Tomita Yukihiro, Feng Zhen, Cheng Jun, Hong Wen-Yu, Pan Yu-Dong, Yang Qing-Wei, Duan Xu-Ru and HL-2A Team 025205 Characterization of plasma current quench during disruption in EAST tokamak Chen Da-Long, Granetz Robert, Shen Biao, Yang Fei, Qian Jin-Ping and Xiao Bing-Jia

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

026101 Quartic coupling and its effect on wetting behaviors in nematic liquid crystals Zeng Ming-Ying, Holger Merlitz and Wu Chen-Xu 026102 Dynamics of a ±1/2 defect pair in a confined geometry: A thin hybrid aligned nematic cell Lu Li-Xia and Zhang Zhi-Dong 026201 Effect of twin boundary on nanoimprint process of bicrystal Al thin film studied by molecular dynamics simulation Xie Yue-Hong, Xu Jian-Gang, Song Hai-Yang and Zhang Yun-Guang 026501 Effects of in-plane stiffness and charge transfer on thermal expansion of monolayer transition metal dichalcogenide Wang Zhan-Yu, Zhou Yan-Li, Wang Xue-Qing, Wang Fei, Sun Qiang, Guo Zheng-Xiao and Jia Yu

(Continued on the Bookbinding Inside Back Cover) 026801 Coadsorption of gold with chlorine on CeO2 (111) surfaces: A first principles study Lu Zhan-Sheng, He Bing-Ling, Ma Dong-Wei and Yang Zong-Xian 026802 Effect of the thickness of InGaN interlayer on 푎-plane GaN epilayer Wang Jian-Xia, Wang Lian-Shan, Zhang Qian, Meng Xiang-Yue, Yang Shao-Yan, Zhao Gui-Juan, Li Hui-Jie, Wei Hong-Yuan and Wang Zhan-Guo

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTI- CAL PROPERTIES

027101 Breakdown mechanisms in AlGaN/GaN high electron mobility transistors with different GaN channel thickness values Ma Xiao-Hua, Zhang Ya-Man, Wang Xin-Hua, Yuan Ting-Ting, Pang Lei, Chen Wei-Wei and Liu Xin-Yu 027201 Localization correction to the anomalous Hall effect in amorphous CoFeB thin films Ding Jin-Jun, Wu Shao-Bing, Yang Xiao-Fei and Zhu Tao 027301 Influence of interface within the composite barrier on the tunneling electroresistance of ferroelectric tunnel junctions with symmetric electrodes Wang Pin-Zhi, Zhu Su-Hua, Pan Tao and Wu Yin-Zhong 027302 Transport mechanism of reverse surface leakage current in AlGaN/GaN high-electron mobility transis- tor with SiN passivation Zheng Xue-Feng, Fan Shuang, Chen Yong-He, Kang Di, Zhang Jian-Kun, Wang Chong, Mo Jiang-Hui, Li Liang, Ma Xiao-Hua, Zhang Jin-Cheng and Hao Yue

027303 Improved performance of AlGaN/GaN HEMT by N2O plasma pre-treatment Mi Min-Han, Zhang Kai, Zhao Sheng-Lei, Wang Chong, Zhang Jin-Cheng, Ma Xiao-Hua and Hao Yue 027304 Morphology-controlled preparation of tungsten oxide nanostructures for gas-sensing application Qin Yu-Xiang, Liu Chang-Yu and Liu Yang

027305 Synthesis and electrical properties of In2O3(ZnO)m superlattice nanobelt Tang Xin-Yue, Gao Hong, Wu Li-Li, Wen Jing, Pan Si-Ming, Liu Xin and Zhang Xi-Tian

−1 027401 Evolution of the 128-cm Raman phonon mode with temperature in Ba(Fe1−푥Co푥)2As2 (푥 = 0.065 and 0.2) Yang Yan-Xing, Gallais Yann, Fang Zhi-Hao, Shi Jing and Xiong Rui 027501 Quantum phase transition and Coulomb blockade effect in triangular quantum dots with interdot ca- pacitive and tunnel couplings Xiong Yong-Chen, Wang Wei-Zhong, Yang Jun-Tao and Huang Hai-Ming 027502 Schwinger-boson approach to anisotropy ferrimagnetic chain with bond alternation Li Yin-Xiang and Chen Bin 027503 Room-temperature ferromagnetism with high magnetic moment in Cu-doped AlN single crystal whiskers Jiang Liang-Bao, , Zuo Si-Bin and Wang Wen-Jun

(Continued on the Bookbinding Inside Back Cover) 027504 Effects of growing conditions on the electric and magnetic properties of strained La2/3Sr1/3MnO3 thin films Lu Hai-Xia, Wang Jing, Shen Bao-Gen and Sun Ji-Rong 027505 Magnetization reversal process in Fe/Si (001) single-crystalline film investigated by planar Hall effect Ye Jun, He Wei, Hu Bo, Tang Jin, Zhang Yong-Sheng, Zhang Xiang-Qun, Chen Zi-Yu and Cheng Zhao-Hua 027801 Hole transporting material 5, 10, 15-tribenzyl-5H-diindolo[3, 2-a:30, 20-c]-carbazole for efficient opto- electronic applications as an active layer Zheng Yan-Qiong, William J. Potscavage Jr, Zhang Jian-Hua, Wei Bin and Huang Rong-Juan

027802 Elastic, dielectric, and piezoelectric characterization of 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 single crys- tal by Brillouin scattering Fang Shao-Xi, Tang Dong-Yun, Chen Zhao-Ming, Zhang Hua and Liu Yu-Long 027803 Synthesis and microwave absorption properties of graphene–oxide(GO)/polyaniline nanocomposite with

Fe3O4 particles Geng Xin, He Da-Wei, Wang Yong-Sheng, Zhao Wen, Zhou Yi-Kang and Li Shu-Lei 027804 High-frequency properties of oil-phase-synthesized ZnO nanoparticles Ding Hao-Feng, Yang Hai-Tao, Liu Li-Ping, Ren Xiao, Song Ning-Ning, Shen Jun, Zhang Xiang-Qun, Cheng Zhao-Hua and Zhao Guo-Ping

027901 Temperature effect on the electronic structure of Nb:SrTiO3 (100) surface Zhang Shuang-Hong, Wang Jia-Ou, Qian Hai-Jie, Wu Rui, Zhang Nian, Lei Tao, Liu Chen and Kurash Ibrahim

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY 028101 Defect reduction in GaAs/Si film with InAs quantum-dot dislocation filter grown by metalorganic chem- ical vapor deposition Wang Jun, Hu Hai-Yang, Deng Can, He Yun-Rui, Wang Qi, Duan Xiao-Feng, Huang Yong-Qing and Ren Xiao-Min

028102 Influence of substrate bias voltage on the microstructure of nc-SiO푥:H film Li Hui-Min, Yu Wei, Xu Yan-Mei, Ji Yun, Jiang Zhao-Yi, Wang Xin-Zhan, Li Xiao-Wei and Fu Guang-Sheng 028103 Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots Alireza Samavati, Z. Othaman, S. K. Ghoshal and M. K. Mustafa 028104 Influence of colloidal particle transfer on the quality of self-assembling colloidal photonic crystal under confined condition Zhao Yong-Qiang, Li Juan, Liu Qiu-Yan, Dong Wen-Jun, Chen Ben-Yong and Li Chao-Rong 028501 Baseline optimization of SQUID gradiometer for magnetocardiography Li Hua, Zhang Shu-Lin, Qiu Yang, Zhang Yong-Sheng, Zhang Chao-Xiang, Kong Xiang-Yan and Xie Xiao- Ming 028502 One-dimensional breakdown voltage model of SOI RESURF lateral power device based on lateral lin- early graded approximation Zhang Jun, Guo Yu-Feng, Xu Yue, Lin Hong, Yang Hui, Hong Yang and Yao Jia-Fei

(Continued on the Bookbinding Inside Back Cover) 028503 Nonlinear properties of the lattice network-based nonlinear CRLH transmission lines Wang Zheng-Bin, Wu Zhao-Zhi and Gao Chao 028504 Mapping an on-chip terahertz antenna by a scanning near-field probe and a fixed field-effect transistor Lu¨ Li, -Dong, Roger A. Lewis, Sun Yun-Fei, Wu Dong-Min, and Qin Hua 028505 Energy transfer ultraviolet photodetector with 8-hydroxyquinoline derivative-metal complexes as accep- tors Wu Shuang-Hong, Li Wen-Lian, Chen Zhi, Li Shi-Bin, Wang Xiao-Hui and Wei Xiong-Bang 028701 Stretching instability of intrinsically curved semiflexible biopolymers: A lattice model approach Zhou Zi-Cong, Lin Fang-Ting and Chen Bo-Han 028702 Controlling cooperativity of a metastable open system coupled weakly to a noisy environment Victor I. Teslenko, Oleksiy L. Kapitanchuk and Zhao Yang 028703 Fast parallel algorithm for three-dimensional distance-driven model in iterative computed tomography reconstruction Chen Jian-Lin, Li Lei, Wang Lin-Yuan, Cai Ai-Long, Xi Xiao-Qi, Zhang Han-Ming, Li Jian-Xin, Yan Bin 028704 Multiple optical trapping based on high-order axially symmetric polarized beams Zhou Zhe-Hai and Zhu Lian-Qing

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

029201 Changing characteristics and spatial differentiation of spring precipitation in during 1961–2012 -Lan, Zhang Qiang, Zhang Jun-Guo, Hu Wen-Chao, Guo Jun-Qin and Wang Sheng