Prism Pair Research Articles

Modeling of compliant-based support for large aperture rotary prisms with horizontal-axis

In the Thirty-Meter-Telescope (TMT), a pair of wedge prisms with diameters of approximately 1500 mm are proposed to mitigate atmospheric dispersion across different zenith angles. This is achieved through controlled linear and rotary movements of the prisms. However, providing stable support for such large aperture prisms, with variable cross-sections and capable of rotating 360° around a horizontal optical axis, poses a significant challenge. This paper introduces a compliant-based support method tailored for TMT’s large aperture prisms. The methodology involves a mechanical analysis of the wedge prism with push-pull forces combination, followed by the development of the support principle based on degrees of freedom and constraints analysis. Subsequently, numerical modeling is conducted using compliant elements as the fundamental units. Furthermore, an integrated optomechanical analysis is performed to evaluate the performance of the support. The findings demonstrate that employing this support method results in superior optical surface accuracy under the coupled conditions of gravity and temperature, particularly for prisms with large apertures, variable cross-sections, and rotational capabilities.

638-nm laser-diode pumped alexandrite femtosecond laser passively mode-locked by single-walled carbon nanotubes

A passively mode-locked alexandrite laser was developed with a single-walled carbon nanotubes (SWCNTs) saturable absorber (SA), which was pumped by a 638 nm red laser. After using a pair of prisms for dispersion compensation, the narrowest pulse width of 70 fs was achieved at a repetition rate of 100 MHz. The mode-locked laser had a signal-to-noise ratio greater than 55 dB and a beam quality factor of less than 1.13. A high average output power of 386 mW was achieved with a slope efficiency of 12.4%. It is the first time a passively mode-locked alexandrite femtosecond laser pumped by a 638 nm red laser has been developed. Moreover, it is also the first time that SWCNTs are used as SAs to achieve a passively mode-locked laser in the visible light range.

Tunable non-polarizing optical bandpass filtering in prism pair coupled planar optical waveguide.

A tunable non-polarizing optical bandpass filter structure, comprising a prism pair coupled planar optical waveguide (POW), is demonstrated, by changing the incident angle of the filter. Experimental measurements show that pass bands for both TM and TE polarized waves are present in the filter simultaneously, and the two passbands overlap on each other. The overlapping of the two passbands can be sustainable for the peak wavelength from 623 to 852 nm as the incident angle of the light tuned within 2°. This POW based optical bandpass filter can be potentially applicable in various fields of optical and laser spectroscopies.

Sub-50-fs Kerr-lens mode-locked Yb-doped fluoride laser with 44% optical efficiency.

Yb-doped fluoride has been demonstrated to be potential crystals for application in efficient ultrafast lasers. However, the trade-off between the shorter pulses with higher efficiencies is a challenge. In this work, using Y b,G d:C a S r F 2 crystal, we report on a sub-50-fs Kerr-lens mode-locked oscillator with an optical efficiency up to 44%. Pumped by a 976-nm diffraction-limited fiber laser and using chirped mirrors combined with prism pairs for the dispersion compensation, a pulse as short as 46fs was obtained with 620-mW output power, corresponding to an optical efficiency more than 40%. Stable Kerr-lens mode-locking with RMS of output power lower than 0.3% and beam quality factors M 2<1.14 were achieved. Moreover, a maximum output power of 780mW was obtained in continuous-wave operation with 55.3% optical efficiency. To the best of our knowledge, the results in this work represent the shortest pulses generated from Yb-doped fluoride lasers as well as the highest optical efficiencies ever reported in sub-100fs Yb bulk lasers.

A highly sensitive torsion sensor based on upright-inverted alternating triangular prism structure on the single-multi-single mode fiber

In this paper, a novel torsion sensor based on Mach-zehnder interferometer (MZI) is proposed and demonstrated. The proposed sensor is fabricated by the single-mode fiber (SMF) and multi-mode fiber (MMF) shear splicing, further employing CO2 laser to modulate the MMF surface into triangular prism form. And compare the number of different triangular prism pairs structure on torsion sensitivity. By increasing the number of triangular prism pairs effectively improve the torsion sensitivity. The experimental results show that in the range of 0–9.617 rad/m, the highest sensitivity fiber sensor can be obtained with a sensitivity of 3.3133 nm/(rad/m). Meanwhile, the temperature characteristic of the sensor is investigated, which presents a sensitivity of 21.67 pm/℃ in the range from 30 ℃ to 100 ℃. Therefore, the temperature crosstalk is 0.0065 (rad/m)/℃, which results in a low temperature crosstalk. In addition, the structure also has the advantages of low cost and simple manufacturing process.

ON SMALL CONTINENTAL MAMMOTHS AND DWARFISM

In the evolution of proboscideans, the appearance of dwarf and semi-dwarf forms occurred repeatedly, in different territories and at different times, due to a lack of resources caused by geographic isolation on islands and by landscape isolation on the mainland. Despite a significant amount of information on the insular forms of mammoths and elephants, the question of the relationship between a decrease in body size and morphological changes in the dental system remains a matter of debate. Some data show that dwarfism was accompanied by a decreasing number of plates (lophs) and by tooth enamel thickening. Other data show that changes in the dental system on the islands indicate that the number of plates could either decrease or remain unchanged, or even increase. Taking into account the importance of the number of plates as a diagnostic feature in the species identification of proboscidean taxa and the lack of a consensus on the stability of the trend towards a decrease in the number of plates from large continental ancestors to insular dwarf descendants, we (1) summarize the data on the records of small tooth-mammoths of the genus Mammuthus with a reduced number of plates in sites across northern Eurasia, (2) provide new radiocarbon dates, and (3) consider the number of plates as a possible sign of dwarfization in continental mammoths. The small teeth of the last generation of M. primigenius from the coastal part of northeastern Siberia and a comparison with data from other regions show that the posterior sections of mammoth cheek teeth are the most variable and represent a reduction complex. For the woolly mammoth, reduction primarily affects that part of the crown which became more complex by the gradually increasing number of plates during the phyletic evolution in the Middle to Late Pleistocene. The rapid loss of the evolutionary achievements through reduction is not a unique feature of woolly mammoth teeth. This has been observed in other mammals as well. Similar reduction complexes are observed for the cheek teeth of proboscideans and rodents of the subfamily Arvicolinae, as is shown by a decrease in the number of serially homologous crown elements: plates in proboscideans and pairs of prisms in voles. A comparison of the number of plates with the size of the teeth of M. primigenius suggests that a decrease in the number of dental plates, while retaining other specific features of the tooth, can be used as a criterion for separating semi-dwarf and small specimens of the woolly mammoth. The largest decrease in size of mainland mammoths is observed during warming periods, which also showed significant transformations of landscapes in a reduction of available resources.

Beam smoothing by introducing spatial dispersion for high-peak-power laser pulse compression.

Post-compression can effectively further improve the peak power of laser pulses by shortening the pulse duration. Which has been investigated in various ranges of energy and central wavelength. However, the spatial intensity profile of high-peak-power laser pulses is generally inhomogeneous due to pump lasers, imperfect optical components, and dust in the optical layout. In post-compression, the B-integral is proportional to intensity, and wavefront distortions are induced in the spectral broadening stage, leading to a decrease in focusing intensity. Moreover, the beam intensity may be strongly modulated and beam inhomogeneity will be intensified in this process, causing damage to optical components and limiting the achievement of high peak power enhancement. In this study, to address these challenges, the laser pulse is first smoothed by introducing spatial dispersion using prism pairs or asymmetric four-grating compressors, and then the smoothed pulse is used for post-compression. The simulation results indicate that this method can effectively remove hot spots from laser pulses and maintain high peak power enhancement in post-compression.

A Generic and Effective System Dispersion Compensation Method: Development and Validation in Visible-Light OCT

Compared with optical coherence tomography (OCT) in the near-infrared domain, the visible-light OCT (vis-OCT) system affords a higher axial resolution for discerning subtle pathological changes associated with early diseases. However, the significant material dispersion at the visible-light range leads to a severe problem for dispersion management in vis-OCT systems, which results in a compromised axial resolution. While dispersion compensators (such as prism pairs) are commonly used, a digital method is still highly desirable and has been widely used to compensate for the residual dispersion imbalance between the reference and sample arms in an OCT system. In this paper, we develop a generic approach to effectively compensate for the system dispersion, especially the higher-order dispersion in the vis-OCT system, by using a single arbitrary measurement of the mirror-reflection (SAMMR) method and its resulting phase information. Compared with the previous methods, including the method based on the Taylor series iterative fitting and differential method, the proposed method does not need to extract the dispersion coefficients or use the metric functions and affords a better performance for axial resolution and the signal-to-noise ratio in vis-OCT systems. Its effectiveness is further validated in an OCT system operating in the near-infrared domain.

High-Bunch-Charge and High-Energy-Gain Inverse-Cherenkov Particle Accelerator With Prebunched Beam

Dielectric laser accelerator (DLA) is a promising candidate for next-generation on-chip particle accelerator. However, practical applications of DLA to date have been restricted due to low accelerated bunch charge and low energy gain, especially for subrelativistic particles. To break through these limitations, here we propose a multistage DLA scheme with inverse Cherenkov effect. The first stage, formed by a pair of symmetric dielectric prisms, is to prebunch a long (tens to hundreds of laser-wavelengths) electron beam with relatively high bunch charge (several to tens of femto-coulombs) via velocity bunching. The subsequent stages, consisting of pairs of dielectric prism stacks, are to fulfill cascade acceleration of the prebunched beam. The synchronization of subrelativistic particles with laser field is realized via adjusting the prism angles in each stack. With theoretical analyses and simulations, we obtain an energy gain of more than 400 keV for an electron beam with initial energy of 100 keV. Compared with that of a non-prebunched beam, the accelerated bunch charge of a prebunched beam is more than four times higher. This proposed scheme affords an effective way of developing an on-chip particle accelerator with high energy gain and high bunch charge.

Two-photon fluorescence imaging using a tunable spectral window based on fiber supercontinuum.

Two-photon excitation fluorescence (TPEF) microscopy has evolved into a versatile tool in biological research. However, the multiplexing capability of TPEF microscopy is limited by the narrow spectral bandwidth of the light source. In this study, we apply a photonic crystal fiber in TPEF microscopy to broaden the excitation source bandwidth. We tuned the spectral window using a spatial light modulator as a programmable diffraction grating that was placed behind a prism pair. In addition, we combined a grating pair to compensate for dispersion to improve the two-photon excitation efficiency. The combination of a broad spectrum and a programmable grating enabled fast spectral window tuning rate on a time scale of tens of milliseconds. We demonstrate the performance of our method by imaging live B16 cells labeled with four emission spectrum overlapped fluorescent proteins.

Valley transport via dual-band elastic topological edge states in local-resonant phononic crystal plate

Most previously reported Dirac valley degeneracies in continuous phononic crystal plates originate from Bragg scattering of the structures and generally have only single-band elastic-wave topological edge states. In the present work, a pair of triangular prisms is used in the construction of hexagonal-lattice phononic crystal plates to mimic the dual-band elastic valley Hall effect. Based on the spatial inversion symmetry conditions, which are related to the intrinsic frequencies of the resonators, the valley degeneracies, topological nontrivial bandgaps, and energy band inversion characteristics of multiple resonance modes are investigated by using the finite element method. Edge passbands combining distinct topology phases exist in each of the two nontrivial bandgaps of the ribbon configuration. The full-field simulations for flexural waves in the waveguide structure are demonstrated to support topologically valley-protected edge transmission in both bands, which immunizes the transport against backscattering from large corners and defects in the route. This work provides a reference for valley edge protection in subwavelength continuous elastic plate media and for the manipulation of the elastic waves at multiple frequencies.

Cumulative ejection of terahertz radiation from a laser-driven magnetized plasma

We propose a scheme for efficient directional emission of laser-driven wakefields from a magnetized plasma. In the scheme, a laser–plasma interaction region is sandwiched between a pair of dielectric prisms of total internal reflection. The wakefields, propagating in the plasma at different angles to the laser beam, are cumulated by the prisms and radiated to free space in the direction of the laser beam. For magnetic fields &amp;lt;100 T, a 50-fs laser pulse with 1-J energy can generate long lasting (hundreds of ps) multicycle terahertz radiation with mJ-level energy. For a 500-T field, the laser pulse can generate terahertz bursts with a uniform spectrum in the ∼7–14 THz interval with ten-mJ-level energy.

Design of the quadrangular prism beam splitting receiving system in the MEMS-based scanning LIDAR.

The detector bandwidth and photosensitive surface aperture are the key parameters in the high-precision and high-definition scanning 3D imaging LIDAR system, which usually require a high detector bandwidth and large photosensitive surface aperture. In order to solve the problem of a high bandwidth and small photosensitive surface of existing InGaAs detectors, this paper proposes a beam splitting method using a pair of quadrangular prisms to realize beam splitting the reception of return laser beams, which increases both the receiving field of view (FOV) and the effective photosensitive surface of the detector. The principle and structure of the prism beam splitter are discussed; a beam splitting receiving optical system with a pair of quadrangular prisms is presented, and the beam splitting effect verified by its simulation experiment is analyzed. With this novel, to the best of our knowledge, light splitting receiving method, the receiving FOV can be effectively increased to ±5∘, and the effective photosensitive surface aperture of the detector can be increased from 0.5 to 1.0mm.

Bandwidth-Enhanced Circularly Polarized Slot Antenna and Array Under Two Pairs of Degenerate Modes in a Single Resonant Cavity

A novel design concept of bandwidth-enhanced full-metal circularly polarized (CP) cavity-backed slot antenna and array based on two pairs of degenerate modes in a single cavity is proposed in this paper. Conventional CP antenna based on one pair of degenerate modes only has one axial-ratio (AR) minima and causes a narrow AR bandwidth. Two pairs of degenerate modes in a proposed multimode cavity resonator can initially produce two separate CP operating bands. Then, a pair of metal prisms is introduced to allocate the two bands in proximity to each other, thus obtaining a wide operating bandwidth with two AR minima. As the radiation slots are directly fed by the electric field of the cavity modes, 2 × 2 cross slots are placed on the top wall so as to comprise a CP array. As such, a very simple wideband CP antenna array is realized by virtue of a single multiple-mode resonator without needing extra power dividers. Finally, the 2 × 2 wideband CP antenna array is fabricated and measured. Measurement shows that the proposed antenna array can achieve 15% bandwidth, a peak gain of 11.8 dBic, and a peak total efficiency of 96%.

Symmetries of Scan Patterns of Laser Scanners with Rotational Risley Prisms

Laser scanners with rotational Risley prisms produce scan patterns that can be classified as a type of rhodonea curve, because of their symmetry. The present study builds upon the novel, graphical method that we have developed to simulate and analyze such patterns using a commercially available mechanical design program, CATIA V5R20 (Dassault Systems, Paris, France). This graphical method has both the advantage of simplicity (regarding analytical methods) and of generating exact scan patterns (in contrast to approximate methods). The aim of this work is to utilize this method to study symmetry properties of scan patterns produced by a pair of rotational Risley prisms. A multi-parameter analysis is performed, considering the characteristic parameters of the approached scanner: refractive indexes and angles of the prisms, as well as their rotational velocities. Furthermore, Marshall’s parameters are considered: ratios of the rotational velocities and of the prism angles. Because the symmetries are identical for scan patterns generated by all the four possible configurations of a pair of prisms (and only their dimensions are different), the shape of these patterns is studied only for one of these configurations. Therefore, without losing generality, the symmetries of the patterns produced by such scanners are determined, as well as some of their characteristic dimensions. Rules-of-thumb were obtained to be able to generate patterns that are appropriate for a specific application. Moreover, we demonstrated that the existing symmetries simplify the process of obtaining the scan patterns by identifying repetitive parts (defined as structures of symmetry) of a pattern.

Using an inexpensive module for Quantitative Phase Imaging

We report on modular implementation of digital holography that we recently proposed. The module is designed such that it may be added to an existing brightfield microscope’s image port for digital holographic microscopy functionality. The proposed system is modular, portable, and cost-effective and not require path-length realignment when changing samples. The square in-line Mach-Zender architecture is used and the off-axis condition is achieved using two sets of wedge prism pairs; this approach offers advantages over other Mach-Zender nearly common-path modules, particularly in path length matching of object and reference wavefields for low-temporal coherence sources. Additionally, the proposed system allows for continuous variation of the tilt angles of the object and reference wavefields incident on the sensor, making it readily adaptable to any microscope and camera.

Design and Testing of a Compact Optical Angle Sensor for Pitch Deviation Measurement of a Scale Grating with a Small Angle of Diffraction

The design and testing of different optical heads were performed to evaluate the pitch deviation of a diffraction scale grating with a small diffraction angle. Based on the proposed pitch deviation evaluation method employing optical angle sensors based on laser autocollimation, a modified optical head with position-sensitive detectors (PSDs) is first designed and constructed by following the conventional optical configuration. Owing to the small angle of diffraction of the first-order diffracted beams, the modified optical head has a large working distance, resulting in poor sensor stability. Therefore, a novel and compact optical head employing a pair of small prisms is designed and developed to shorten the working distance of the optical head. An additional modification was also made to the developed compact optical head in such a way that collimator objectives (COs) in the laser autocollimation units are removed to improve the sensor sensitivity. Experimental comparisons were conducted using the three types of optical heads to verify the feasibility of the developed optical angle sensor with PSDs.

Beam Smoothing Based on Prism Pair for Multistep Pulse Compressor in PW Lasers

Ultra-short, ultra-intense lasers provide unprecedented experimental tools and extreme physical conditions, enabling the exploration of the frontiers of basic physics. Recently, a multistep pulse compressor (MPC) method was proposed to overcome the limitations of the size and the damage threshold of gratings in the compressor for the realization of a higher-peak-power laser. In the MPC method, beam smoothing is an important process in the pre-compressor. In this study, beam smoothing based on prism pairs is investigated, and the spatial profiles, as well as spectral dispersion properties, are analyzed. The simulation results demonstrate that the prism pair can effectively smooth the laser beam. Furthermore, beam smoothing is found to be more efficient with a shorter separation distance if two prism pairs are arranged to induce spatial dispersion in one or two directions. The beam smoothing results obtained in this study will help optimize optical designs in petawatt (PW) laser systems, thereby improving their output and operational safety.

Time-of-flight measurement-based three-dimensional profiler system employing a lightweight Fresnel-type Risley prism scanner

A time-of-flight measurement-based three-dimensional (3D) profiler system employing a lightweight scanning system is demonstrated. To reduce the weight of the scanning system, and thereby achieve faster scanning speeds, two Fresnel prism sheets were employed as the scanning optics and installed to work as a pair of Risley prisms. Each Fresnel prism sheet has a diameter of 102 mm and mass of 15 g, which is about 12 times lighter than ordinary bulky prism. By scanning the laser beam with the developed scanning system, a 3D point cloud image of a target object located 8 m away could be successfully obtained. The image distortion was removable by correcting six geometrical parameters of the scanner using a simple optimization algorithm. It was confirmed by the experiment that once the distortion has been corrected, it is valid for other scanning speeds (and trajectories), enabling 3D profile measurements that do not require postprocessing of measured data. Measurement results for a standard target composed of square extrusions were in good agreement with the reference values, with deviations of <1 mm.

Attosecond stable dispersion-free delay line for easy ultrafast metrology

We demonstrate a dispersion-free wavefront splitting attosecond resolved interferometric delay line for easy ultrafast metrology of broadband femtosecond pulses. Using a pair of knife-edge prisms, we symmetrically split and later recombine the two wavefronts with a few tens of attosecond resolution and stability and employ a single-pixel analysis of interference fringes with good contrast using a phone camera without any iris or nonlinear detector. Our all-reflective delay line is theoretically analyzed and experimentally validated by measuring 1st and 2nd order autocorrelations and the SHG-FROG trace of a NIR femtosecond pulse. Our setup is compact, offers attosecond stability with flexibility for independent beam-shaping of the two arms. Furthermore, we suggest that our compact and in-line setup can be employed for attosecond resolved pump-probe experiments of matter with few-cycle pulses.