Holographic grating recorded by He–Ne laser operating at 632.8 nm in polymer film containing push–pull azo dye

Holographic gratings were optically recorded by two beams from a He–Ne laser operating at 632.8 nm in poly (methyl methacrylate) (PMMA) film containing push–pull azo dye. The holographic characteristics of the recorded gratings were dependent on the polarization direction of the recording beams and the relationship between the diffractive signals and the power density of recording beams was investigated. The formation of holographic gratings accompanied by 532 nm (double-frequency of Nd:YAG laser) irradiation was studied in detail. It was found that the effect of 532 nm laser to the holographic grating lay in two aspects. The acceleration effect of 532 nm laser to the formation of holographic grating is predominant when the power density of 532 nm laser is low. While at relatively high power density of 532 nm laser, the erasure is the main factor to the holographic grating. Moreover, the holographic grating was probed by 532 nm laser at low power density and the dependence of the first order diffractive signal on the recording beam power density was also presented.     

Influence of two-dimensional bragg diffraction on the competition of the waveguide TE<Subscript>0</Subscript> and TM<Subscript>0</Subscript> modes during formation of spontaneous gratings in AgCl-Ag thin films

An intricate space-time instability of patterns of small-angle scattering and diffraction of a laser beam on the structures appearing in AgCl-Ag films under exposure to the same beam is investigated. The instability is related to the formation of spontaneous gratings in the film resulting from the interference of the incident beam with the waveguide modes scattered in the film. The existence of a two-dimensional Bragg diffraction on the TE₀ and TM₀ modes with subsequent formation of secondary spontaneous gratings is revealed and is theoretically substantiated. It is established that the difference in the indicatrices of the radiation scattered into the TE₀ and TM₀ modes for the s-and p-polarizations manifests itself in different kinds of diffraction and small-angle scattering patterns at the output of illuminated samples.     

Field structure in a photorefractive holographic grating in a planar waveguide

A theoretical investigation is made of the field structure in a holographic grating formed by TE₀ modes in a planar photorefractive waveguide by the photogalvanic recording mechanism. Waveguides with three characteristic refractive index profiles are considered, namely, a step function, a parabola, and a hyperbolic secant squared. A comparison is made between the light field distributions of TE₀ modes in waveguides having the different profiles. The field structure of the space charge in planar holographic gratings is analyzed for their initial formation phase. It is shown that the space charge field has a similar structure for all three waveguide types considered when planar photorefractive gratings are recorded by TE₀ modes.Institute of Automated Control Systems and Radio Electronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 85–92, November, 1993.     

Analysis and design of grating couplers

Based on an accurate perturbation analysis of the guiding properties of dielectric gratings, simple design criteria are developed for grating couplers which transfer the energy of a beam into or out of an optical waveguide. Gratings having arbitrary groove shapes are considered and explicit formulae are given for the leakage parameters of gratings with symmetric profiles. The results cover TE_v and TM_v modes and they apply to both shallow and deep grating grooves. The variation of the leakage parameter α in rectangular gratings is examined in detail; these rectangular gratings are then used as basic configurations for predicting the characteristics of other grating profiles. Particular attention is given to trapezoidal and triangular profiles and gratings with asymmetric profiles are also discussed.     

Spatial-temporal instability and optical turbulence upon the formation of spontaneous gratings by S-polarized light in waveguide AgCl-Ag films

The spatial-temporal instability of the spontaneous gratings formed in waveguide AgCl-Ag films under irradiation with an S-polarized laser beam is investigated. The studies are based on the simultaneous observation of diffraction (D) patterns formed by the S _? gratings and small-angle scattering (SAS). The transverse instability of D and SAS patterns was found to be associated with excitation of TE₀ modes at different angles with respect to the plane of incidence by scattering centers of Rayleigh type with the following formation of microgratings by the scattered modes and with their competition. It is shown that the time evolution of the form and the dynamic shift of the D patterns is also connected with the time dependence of the effective refractive index for TE₀ modes. In the case when a focused laser beam was used, the optical turbulence was found in the SAS and D patterns, caused, mainly, by the competition of S _?-and S ₊-microgratings, which eventually leads to the destruction of the latter.     

Subwavelength lithography using metallic grating waveguide heterostructure

We present subwavelength periodic gratings achieved by employing a metallic grating waveguide heterostructure (MGWHS). The mask can be designed to make one of its diffraction order (±mth) waves resonate with the surface plasmon wave supported by the MGWHS. With a finite-difference time-domain method, we numerically demonstrate that one-dimensional periodic structure of about 60 nm feature, which is far beyond the diffraction limit, can be patterned with the interference of the 3rd diffraction order waves of the mask at a wavelength of 546 nm. The technique can also be extended to two-dimensional patterns using circularly polarized incidence and for the incidence with an angle θ.     

104 nm period grating fabrication in fused silica by immersion two-beam interferometric laser induced backside wet etching technique

A substantial extension of the method of two-beam interferometric laser induced backside wet etching (TWIN-LIBWE), the immersion TWIN-LIBWE, is used to fabricate fused silica gratings with a 104 nm period. The spatially filtered fourth harmonic of Nd:YAG laser (λ=266 nm, τ_FWHM=8 ns) pulses were split into two parts which then interfered at the backside of the fused silica target in contact with a liquid absorber (naphthalene methyl methacrylate saturated solution with a concentration of 1.85 mol/dm³). The hypotenuse of a rectangular fused silica prism is attached to the fused silica target with the use of distilled water as the immersion liquid. On steering the beams through the sides of the prisms, the angle between the two laser beams has been substantially increased. The resulting period of 104 nm is the minimal grating constant achievable under such experimental conditions and, to our knowledge, the smallest laser generated grating period in fused silica at present. PACS 42.62; 42.79; 81.65     

Charging of glassy chalcogenide semiconductors in corona discharge and its effect on holographic grating formation

Recording of optical holographic gratings based on photostructural transformations in thin (≈ 1 μm) As₂S₃ and As₂S₃ semiconductor layers in the presence and absence of a corona discharge and also chemical etching of these gratings are studied. Initiation of a corona at the stage of interference grating recording is shown to improve the exposure contrast of metal-glassy chalcogenide semiconductor thin-film structures. The holographic sensitivity, diffraction efficiency, dynamic range, and contrast are also improved severalfold. When phase relief gratings formed in these layers are selectively etched in a chemical etchant in the presence of a corona, their profile becomes more regular and deeper by 25–30% and the diffraction efficiency increases by 30–50%.     

Corrugated neat thin-film conjugated polymer distributed-feedback lasers

Wave-guided thin-film distributed-feedback (DFB) polymer lasers are fabricated by spin coating a PPV-derived semiconducting polymer, thianthrene-DOO-PPV, onto oxidised silicon wafers with corrugated second-order periodic gratings. The gratings are written by reactive ion beam etching. Laser action is achieved by transverse pumping with picosecond laser pulses (wavelength 347.15 nm, duration 35 ps). The DFB-laser surface emission and edge emission are analysed. Outside the grating region the polymer film is used for comparative wave-guided travelling wave laser (amplified spontaneous emission (ASE)) studies. The pump pulse threshold energy density for wave-guided DFB-laser action (4–9 μJ cm^-2) is found to be approximately a factor of two lower than the threshold for wave-guided travelling wave laser action. The spectral width of the DFB laser (down to Δλ_DFB≈0.07 nm) is considerably narrower than that of the travelling wave laser (Δλ_TWL≈14 nm). The DFB-laser emission is highly linearly polarised transverse to the grating axis (TE mode). Only at high pump pulse energy densities does an additional weak TM mode build up. The surface-emitted DFB-laser radiation has a low divergence along the grating direction. For both the DFB lasers and the travelling wave lasers, gain saturation occurs at high excitation energy densities. Received: 7 January 2002 / Revised version: 15 February 2002 / Published online: 14 March 2002     

非线性变周期全息光栅的制作

叙述一种用发散光束来的制作变周期光栅的方法,简单的系统保证了两束形成全息干涉的光强相等这一点对获得高反衬结构的光栅图形是重要的。在显影过程中用He-Ne激光作为衍射效率的在位监控。     

Anomalous behaviour of long-time increase in diffraction efficiency of photorefractive grating in Ce：BaTiO3 in dark

Anomalous long-time increase of the diffraction efficiency is observed in dark-decay experiments of photorefractive gratings in Ce：BaTiO3. It is deduced that a phase-conjugate beam is induced by the writing beam at acute angle to the ＋c axis of the crystal and it interferes with the other writing beam to form a second grating which is perpendicular to the first grating formed by the interference between two writing beams. The rising behaviour of the diffraction efficiency results from the different decay rates of these two photorefractive gratings. Furthermore, a simplified model of two gratings, both induced by two deep traps, is proposed to account for this phenomenon and the fitting results agree well with the experimental results.     

利用铌酸锂晶体制作体全息光栅的设计性实验

利用双光束干涉,通过控制双光束的记录角度,在铌酸锂晶体中写入光折变体全息布拉格光栅.将该光栅应用于光通信系统中作为滤波器使用,利用ASE光源和光谱仪对其进行测试,在1 548nm波长处获得了峰值半高全宽为4nm,衍射效率为10%的滤波效果.     

高质量全息光栅实验系统研究

基于全息光栅在信息光学及光谱仪中的重要地位,对全息光栅进行了理论分析,提出了一种新的制作高质量全息光栅的实验系统.该实验系统的优点在于:将激光器发出的高斯光束改造成为均匀平面光波,以此平面光波作为光源可以制作出高质量的全息光栅.     

Polarization holographic and surface-relief gratings at 257 nm in an amorphous azobenzene polyester

Polarization holographic and surface-relief gratings have been recorded in an amorphous azobenzene polyester by use of a frequency-doubled argon-ion laser beam at 257 nm. Higher excited states of azobenzene in the trans and cis configurations contribute to the formation of a diffraction grating in this experiment. A combination of right and left circularly polarized writing beams has been found to give the highest diffraction efficiency. The contributions to the total phase difference that arise from anisotropy and surface relief have been separated experimentally, and it is shown that the surface-relief grating contributes a larger phase difference than that which is due to anisotropy.     

基于PVA／AA光致聚合物的衍射光锥产生机理及其抑制

研究了以He—Ne激光器作为记录光源,以He-Ne、Nd：YAG和He-Cd激光器作为读出光源的亚甲基蓝敏化的PVA／AA体系光致聚合物的全息衍射光锥现象。衍射光锥现象的产生是由于入射光透过全息记录材料内部的不均匀结构或缺陷所产生的噪音光栅所致。运用Ewald球对此现象产生的机理进行了解释,利用全息光散射理论结合三角学...     

Diffraction properties of ultrashort pulsed beams with arbitrary temporal profiles by a reflection volume holographic grating

The diffraction properties of reflection volume holographic gratings are studied when the gratings are illuminated by an ultrashort beam with arbitrary temporal profiles. The modified Kogelnik's theory of coupled waves is used. Simple analytical expressions for spectral and temporal distribution of the transmitted and diffracted are obtained. The dependences of the diffraction bandwidth, the Bragg selectivity bandwidth and the total diffraction efficiency of the reflection volume grating on the temporal profiles of the input ultrashort pulse are investigated. Study shows that the bandwidth of the reflection volume holographic gratings varies with the grating parameters more slowly than the transmitting volume holographic gratings. For three different temporal profiles, numerical results about diffraction properties of the reflection volume holographic gratings are given and compared with the transmitting volume holographic gratings.     

Surface relief diffraction gratings written on <Emphasis Type="BoldItalic">β</Emphasis> -BaB<Subscript>2</Subscript>O<Subscript>4</Subscript> crystal by femtosecond pulses

Surface relief diffraction gratings were written at the entrance surface of a β-BaB₂O₄ (BBO) crystal under irradiation with femtosecond laser pulses. Probe–beam diffraction and atomic force microscopy (AFM) were employed to characterize the diffraction properties and the microstructures of the gratings. The maximal first-order diffraction efficiency of these gratings is approximately 63%. The surface periodic structure of the material induces noncollinear propagation of the fundamental input beam in the crystal. Using this diffractive optical element, efficient generation of multiple second-harmonic beams was achieved. PACS 42.79.Dj; 42.40.Lx; 42.65.–k     

Holographic grating based Ebert spectrograph

In this paper we discuss the aberration properties and design procedure of in-plane Ebert spectrograph using conventional as well as holographic diffraction gratings. In both cases the gratings are situated at the well-known √3-position so that the spectrum can be recorded on a flat surface. It has been found that the holographic grating system has better resolution than the conventional grating system. The design parameters of a medium sized holographic grating spectrograph in which a concave spherical mirror is mounted in the off-axis configuration have been specified. The performance of the spectrograph has been evaluated by plotting spot diagram.     

High spectral resolution analysis of tunable narrowband resonant grating waveguide structures

A high spectral resolution analysis of narrowband reflection filters based on resonant grating waveguide structures is presented. A tunable high-performance dye laser with ∼ 0.15 cm^-1 line width and a beam analyzing system consisting of three simultaneously controlled CCD cameras were used to investigate grating waveguide resonances at wavelengths in the 694 nm and 633 nm ranges. A reflectivity of ∼ 91% and a line width of ∼ 0.55 nm were measured and theoretically modeled for a resonant reflection filter specifically designed for the ruby laser wavelength 694.2 nm. For a second grating waveguide structure, designed for the helium-neon laser emission wavelength 632.8 nm, we observed a thermal shift of its spectral resonance position of several nanometers, when increasing the sample temperature by some degrees. An inverse thermal shift was observed when the structure was subsequently cooled down to room temperature. Our results suggest implementation of grating waveguide devices combining a narrow line width with a tunability of the resonant response into innovative concepts for reflection filter and sensor applications. PACS 42.62.-b; 42.79.Dj; 42.79.Gn     

Tilted and axis-shift Lloyd's mirror system for recording low-density and large-area holographic grating

It is difficult to record holographic gratings of low density (<100 lines/mm) and large area simultaneously using traditional holographic system. In order to produce both low-density and large-area holographic gratings, a tilted and axis-shift (TAS) Lloyd's mirror system was designed for recording such holographic gratings. The recording area will increase largely especially for gratings of low density, by setting the angle between the Lloyd's mirror and the substrate larger than 90°, and meanwhile, by enlarging the intersection angle of incident light and mirror surface. Insuring the projected area onto the substrate by reflex equal to the incident area directly onto the substrate, the optical axis was shifted to realize the maximization of utilization of interference area. The contrast of fringe pattern was analyzed by the coherence for the laser beam in the space and time scale. The TAS Lloyd's mirror system for 60 lines/mm grating in the contrast of 0.8 was optimized, and as a result, the interference area was increased by about 150 times comparing to the traditional Lloyd's mirror system using the Lloyd's mirror of same dimensions.