外文翻譯---通過三維打印技術(shù)快速制備太赫茲透鏡（英文）

1、Rapid fabrication of terahertz lens via three-dimensional printing technologyZhongqi Zhang 1, Xuli Wei 1, Changming Liu 1, Kejia Wang 1,*, Jinsong Liu 1, and Zhengang Yang 21Wuhan National Laboratory for Optoelectronics

2、, Huazhong University of Science and Technology, Wuhan 430074, China2School of Optical and Electronic information, Huazhong University of Science and Technology, Wuhan 430074, China *Corresponding author: wkjtode@sina.co

3、mReceived November 9, 2014; accepted December 22, 2014; posted online February 23, 2015We design a plano-convex lens working in the terahertz (THz) frequency range and fabricate it using three- dimensional (3D) printing

4、technology. A 3D field scanner is used to measure its focal properties, and the results agree well with the numerical simulations. The refractive index and absorption coefficient measurements via THz time-domain spectros

5、copy (THz-TDS) reveal that the lens material is highly transparent at THz frequen- cies. It is expected that this inexpensive and rapid 3D printing technology holds promise for making various THz optical elements. OCIS c

6、odes: 220.3630, 050.6875, 300.6495. doi: 10.3788/COL201513.022201.Terahertz (THz) radiations are electromagnetic waves that are located in the frequency range of 0.1–10 THz. Due to their nonionizing properties, THz waves

7、 have been applied to security scanning, and to noninvasive testing, sensing, and communication[1–5]. To extend the applica- tions of THz technology, optical devices working in the THz regime to manipulate THz waves, suc

8、h as wave plates, splitters, lenses, and waveguides, are in great demand[6,7]. Among all these components, the lenses can focus and collimate the THz beam, serving as the basic optical element in THz imaging systems. Ord

9、inary glasses commonly used at optical frequencies are useless for THz applications, owing to their high extrinsic dielectric losses in the THz range. Fortunately, polymers show excellent transparency in the THz regime.

10、Typical polymers, such as polymethylpentene, high- density polyethylene, and tsurupika, have been widely used to commercially fabricate THz lenses and windows[8–11]. Recently, a great amount of research efforts have been

11、 made to seek easily accessible materials suitable for THz applications. Siemion et al. demonstrated the aberration- correction diffractive paper lens for low-frequency THz radiation[12]. Han et al. suggested the possibi

12、lity of using natural stones as THz components[13]. Unlike traditional refractive bulk devices, which achieve phase delays as light propagates through the thickness of the material, novel flat lenses can create an abrupt

13、 phase shift of the optical resonators right at the surface of the lenses[14–16]. Recently, an ultrathin THz planar lens has been reported, but low energy conversion efficiency has restricted its practical applications[1

14、7]. Recent advances in artificially engineered metamaterials, which show resonance properties in the THz frequency, make it possible to fabricate functional THz devices, such as filters and tubes[18,19].As we know, comme

15、rcial lenses are generally polished via computer numerical control machining, which is com- plicated and time consuming. In recent years, three- dimensional (3D) printing came to the foreground as a very competitive proc

16、ess in terms of cost and speed. Many works have reported on the applications of 3D printed THz devices, including waveguides, woodpile structures, and computer-generated volume holograms[7,20,21]. In our earlier work, 3D

17、 printing technology was employed to make spiral phase plates to generate a THz vortex beam[22,23]. In this Letter, we design, fabricate, and characterize a plano-convex THz lens (Fig. 1). The THz time-domain spectroscop

18、y (THz-TDS) measurement method is used to determine the optical characteristics of the lens material. It should be noted that this printing material is highly transparent in the THz regime, indicating that it is an ideal

19、 material to compose THz components. The design of the lens is implemented using the lens mak- er’s formula, and is assisted by the optical design software ZEMAX[24]. The focusing performance of this lens is characterize

20、d with a THz point scanning system. Exper- imental measurements coincide with the finite difference time-domain (FDTD) simulations. Moreover, this 3DFig. 1. (a) Top view of the printed lens. (b) Side view of the printed

21、lens.COL 13(2), 022201(2015) CHINESE OPTICS LETTERS February 10, 20151671-7694/2015/022201(4) 022201-1 © 2015 Chinese Optics Letterslocated at y ≈ 100 mm. To further investigate its focal properties, the on-axis int

22、ensity distribution behind the lens [cutting along the horizontal dotted line in Fig. 4(a)] is depicted in Fig. 4(b). The on-axis intensity increases gradually, reaches its maximum value, and then decreases as the propag

23、ation distance increases. The maximal axial intensity is located at y ¼ 103 mm. Since the main surface of the plano-convex lens is located at the spherical vertex (y ¼ 6.45 mm), it can be concluded that the foc

24、al length with the FDTD simulation is 103–6.45 ¼ 96.55 mm, close to the value of 97.7 mm obtained in the theoretical results. The radial intensity distribution of the focal spot is shown in Fig. 4(c) [cutting along

25、the vertical dotted line in Fig. 4(a)]. The lateral intensity distribution of the focal spot accords with the Gaussian function, and the spot size is around 5 mm. A point-scanning test is conducted to measure the focal p

26、roperties of the printed lens, with the experimental setup shown in Fig. 5. A 100 GHz Gunn diode (Spacek Labs model GW-102 P) coupled to a frequency tripler is used as the light source. It delivers a Gaussian beam at 300

27、 GHz. The beam is collimated by a spherical lens, then directed to our 3D printed lens and focused behind the lens. The Schottky diode (Virginia Diodes, Inc.), mounted on a motorized X–Y–Z translation stage, is employed

28、to detect the intensity distribution of the THz beam behind the printed lens. An optical chopper at 300 Hz, which is connected to a lock-in amplifier (Stanford Research System SR-830), is used to reduce noise and extract

29、 a reliable signal. The lateral intensity distribution is directly obtained through point scanning (90 mm × 90 mm) on the x–y plane. By varying the distance between the detector and the surface of the printed lens i

30、n steps of 12 mm over a range of 47–155 mm, ten specific positions along the z direction are chosen. Finally, ten intensity profiles are measured. The 2D profiles of the Gaussian beam at five different positions around t

31、he focus are shown in Fig. 6(a). It can be seen that the spot size along the propagation direction reaches its minimum value at two places, but at the dis- tance of 95 mm, the spot energy is more concentrated. The normal

32、ized cross-section plot of the 2D profile at this mini- mum spot size is illustrated in Fig. 6(b). As can be seen from Fig. 6(b), the maximal intensity is not exactly at x ¼ 0 mm. We think this distortion probably c

33、omes from the slight misalignment between the center of thetranslation-stage-scanning range and the spot center, but it has no crucial influence on the scanned profile results. The radial intensity distribution shows a G

34、aussian-shaped profile, in accordance with Fig. 4(c). Then, we fit it with the Gaussian function and find the full width at half-maximum (FWHM) is about 3.5 mm. It is depicted as the red line in Fig. 6(b). Furthermore, w

35、ith this Gaussian function fitting method, we analyze how the FWHM changes with the varying distance. The plot of the beam diameter as a function of the propagation distance is shown as the red curve in Fig. 6(c). We als

36、o analyze the axial intensity distribution. The maximal intensity values at each propa- gation distance are depicted as the blue line in Fig. 6(c). As can be seen, the Gaussian beam has the maximal inten- sity value as w

37、ell as the minimal FWHM at the distance of 95 mm. These experimental results agree well with the expected results. In conclusion, we demonstrate the design, fabrication, simulation, and experimental testing of a 3D print

38、ed THz lens. The printing material exhibits a low absorption coefficient and a stable refractive index over a broad frequency. Our measured focused beam profiles are well explained by the numerical simulation. This 3D pr

39、inted lens has several obvious advantages: it is easily fabricated, effective over a broad THz frequency range, and compat- ible with more complicated geometries. It suggests that the 3D printing technology provides a ne

40、w insight into THz optical elements.This work was supported by the Wuhan Applied Basic Research Project under Grant No. 20140101010009, the National Natural Science Foundation of China under Grant Nos. 61177095, 61475054

41、, and 61405063, the Hubei Natural Science Foundation under Grant No. 2013BAA002, and the Fundamental Research Funds for the Central Universities under Grant Nos. 2013KXYQ004, 2014ZZGH021, and 2014QN023.Fig. 5. Experiment

42、al setup: Transmitter, Gunn Diode; Collimator, spherical lens; Detector, Schottky diode.-20 -15 -10 -5 0 5 10 15 200.00.20.40.60.81.0 (b) (c)Normalized IntensityGaussian fitNormalized Intensityx (mm)FWHM=3.5mm40 60 80 10

43、0 120 140 160 1803456789101112FWHMdistance (mm)FWHM (mm)0.00.20.40.60.81.0 Normalized IntensityNormalized Intensity(a)Fig. 6. (a) 2D Gaussian beam intensity profile images obtained by the point-scanning method. (b) Curve

44、 fitting (the red line) of the measured radial intensity distribution at d ¼ 95 mm. (c) FWHM (the red line) and the axial maximal intensity distri- bution (the blue line) over the propagation distance.COL 13(2), 022