two authors contributed equally to this work.Abstract: Conventional optical components shape the wavefront of propagating light by adjusting the optical path length, which requires the use of rather thick lenses, especially for the adjustment of terahertz (THz) radiation due to its long wavelength. Two ultrathin THz planar lenses were designed and fabricated based on interface phase modulation of antenna resonance. The lens thicknesses were extremely reduced to 100 nm, which is only 1/4000 th of the illuminating light wavelength. The focusing and imaging functions of the lenses were experimentally demonstrated. The ultrathin optical components described herein are a significant step toward the development of a micro-integrated THz system. One-Sentence Summary: Ultrathin planar lenses with a thickness of 100 nm were designed and fabricated to implement THz beam focusing and imaging.Terahertz (THz) radiation lies in the frequency range between infrared and microwaves, typically having wavelengths ranging from 10 μm to 3 mm. THz technology is developing rapidly in many independent fields and has many potential applications (1). However, due to the relatively long wavelengths of THz radiation, most THz components, such as lenses and prisms, are on a large scale and are not suitable for system integration.Conventional optical components shape the wavefront of propagating light via gradual phase changes that accumulate along the optical path, usually via alterations to the spatial distribution using the thickness or refraction index of the components. Early optical components possessed continuous curved surfaces to achieve phase modulation, as indicated in Fig. 1A. This continuity determines the bulkiness of the components. Further technological developments utilized the 2π phase jump to reduce component thickness to the wavelength scale, as shown in Fig. 1B. Subsequently, metamaterials with extremely large effective refractive indices have been used to further reduce the thickness of the optical components (2, 3). However, the basic theory for wavefront shaping is still based on phase accumulation along the optical path, and the thickness of the corresponding components is still quite large. The question remains as to whether it is possible to further reduce the thickness of the optical components.Alternatively, phase changes can also be introduced by an optical resonator. Electromagnetic cavities (4-6), nanoparticles clusters (7,8), and plasmonic antennas (9,10) have previously been employed for tailoring phase changes. Recently, a novel method was proposed to introduce a phase discontinuity at the interface between two media (11)(12)(13). In this method, the geometry of planar V-shaped antennas was spatially selected, and the phase shift between the emitted and illuminating lights could be controlled arbitrarily; the generalized laws of reflection and refraction using this method were described. If the antennas are spatially arranged according to a customized phase distribution, an ultrathin planar optical componen...

Terahertz (THz) technology is a developing and promising candidate for biological imaging, security inspection and communications, due to the low photon energy, the high transparency and the broad band properties of the THz radiation 1-3 . However, a major encountered bottleneck is lack of efficient devices to manipulate the THz wave, especially to modulate the THz wave front. A wave front modulator should allow the optical or electrical control of the spatial transmission (or reflection) of an input THz wave and hence the ability to encode the information in a wave front 4 . Here we propose a spatial THz modulator (STM) to dynamically control the THz wave front with photo-generated carriers. A computer generated THz hologram is projected onto a silicon wafer by a conventional spatial light modulator (SLM). The corresponding photo-generated carrier spatial distribution will be induced, which forms an amplitude hologram to modulate the wave front of the input THz beam. Some special intensity patterns and vortex beams are generated by using this method. This all-optical controllable STM is structure free, high resolution and broadband. It is expected to be widely used in future THz imaging and communication systems.S andwiched between the microwave and infrared, THz radiation has been notoriously difficult to produce, modulate and detect [1][2][3] . Recent progresses such as quantum-cascade lasers 5,6 , terahertz wave generation through a nonlinear crystal 7 and THz time-domain spectroscopy 8 are promoting this subject into one of the most rapidly growing fields. High performance devices to control and manipulate the THz radiation are in urgent demand to develop sophisticated imaging and communication system. The filters, absorbers and polarizers based on graphene, frequency selective surface, metamaterials and photonic crystals have been reported [9][10][11][12][13][14][15][16][17][18] . However, the wave front modulation devices are still lacking. Recently, a novel technology based on the metasurface has been demonstrated to generate the desired wave front distribution 19,20 . Unfortunately, the specific function of this kind of devices has been determined at the moment of their design and could not be flexibly changed any more. The SLM which has been widely used in the visible light band can optically or electrically control the spatial transmission (or reflection) of an input light beam and encode information in the wave front 4 . The SLM always plays an important role in optical information processing, three dimensional image display, optical interconnections and real-time beam shaping. Usually, the SLM is realized through liquid crystals, magneto-optic materials or deformable mirrors. However, such mechanisms cannot work well in the THz regime due to the lack of suitable materials and the size mismatching between the micro-machined components and the THz wavelength 21 . In order to obtain the STM, a novel technology needs to be explored.The STM requires an array of small building blocks that can independentl...

The photodissociation dynamics of 1,3-butadiene at 193 nm have been investigated with photofragment translational spectroscopy coupled with product photoionization using tunable VUV synchrotron radiation. Five product channels are evident from this study: C(4)H(5) + H, C(3)H(3) + CH(3), C(2)H(3) + C(2)H(3), C(4)H(4) + H(2), and C(2)H(4) + C(2)H(2). The translational energy (P(E(T))) distributions suggest that these channels result from internal conversion to the ground electronic state followed by dissociation. To investigate the dissociation dynamics in more detail, further studies were carried out using 1,3-butadiene-1,1,4,4-d(4). Branching ratios were determined for the channels listed above, as well as relative branching ratios for the isotopomeric species produced from 1,3-butadiene-1,1,4,4-d(4) dissociation. C(3)H(3) + CH(3) is found to be the dominant channel, followed by C(4)H(5) + H and C(2)H(4) + C(2)H(2), for which the yields are approximately equal. The dominance of the C(3)H(3) + CH(3) channel shows that isomerization to 1,2-butadiene followed by dissociation is facile.

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The photodissociation dynamics of propyne and allene are investigated in two molecular beam/ photodissociation instruments, one using electron impact ionization and the other using tunable vacuum ultraviolet ͑VUV͒ light to photoionize the photoproducts. The primary dissociation channels for both reactants are C 3 H 3 ϩH and C 3 H 2 ϩH 2. Measurement of the photoionization efficiency curves on the VUV instrument shows that the C 3 H 3 product from propyne is the propynyl (CH 3 CC) radical, whereas the C 3 H 3 product from allene is the propargyl (CH 2 CCH) radical. The dominant C 3 H 2 product from both reactants is the propadienylidene (H 2 CCC) radical. We also observe a small amount of secondary C 3 H 2 product from photodissociation of the C 3 H 3 radicals in both cases.

A terahertz (THz) polarization real-time imaging system that can effectively reduce experimental time consumption for acquiring a sample's polarization information is achieved. An alternative THz polarization measurement method is proposed. In this method, a <110> zinc-blende crystal is used as the sensor, and the probe polarization is adjusted to detect THz electric fields on the two orthogonal polarization components. The relative sensitivity of the imaging system to the THz polarization angle is estimated to be less than 0.5°. To illustrate the ability of the system, two samples are designed and measured by using the system. From their THz polarization real-time images, each region of these samples can be precisely presented. Experimental results clearly show the special influences of different materials on the THz polarization. This work effectively extends the information content obtained by THz real-time imaging and improves the feasibility of the imaging technique.

Spin of light provides a route to control photons. Spin-based optical devices which can manipulate photons with different spin states are imperative. Here we experimentally demonstrated a spin-selected metasurface lens based on the spin-orbit interaction originated from the Pancharatnam-Berry (PB) phase. The optimized PB phase enables the light with different spin states to be focused on two separated points in the preset plane. Furthermore, the metasurface lens can perform the spin-selected imaging according to the polarization of the illuminating light. Such a spin-based device capacitates a lot of advanced applications for spin-controlled photonics in quantum information processing and communication based on the spin and orbit angular momentum.