Fused Silica Prism Research Articles

Silicon nitride (Si3N4) leads to enhanced performance of silica-silver based plasmonic sensor for colorectal cancer detection under optimum radiation damping

Silicon Nitride (Si3N4) possesses large refractive index and transparent behaviour in a broad spectral range from ultraviolet to infrared. These properties of Si3N4 facilitate an efficient light-matter interaction leading to enhanced light confinement. In this work, we have investigated Si3N4-based plasmonic sensor for pathogenic colorectal tissues detection at a wavelength of 1000 nm. The sensor structure consists of fused silica prism and Ag–Si3N4 heterojunction. The figure-of-merit (FOM) of the sensor is optimized by judiciously coordinating the thickness of Ag layer (dM) and Si3N4 layer (dA) under optimum radiation damping (ORD). An optimized FOM as high as 6011 RIU−1 (at dM = 47.3 nm) has been achieved corresponding to dA = 8.6 nm under ORD. At ORD, the corresponding power loss ratio (PLR) is as high as 2.773, and the normalized electric field enhancement factor (FEF) is about 1.06. The magnitude of combined performance factor (CPF), which is the product of FOM, PLR and FEF, of the proposed sensor is as large as 17668.61 RIU−1. The proposed application of Si3N4 in plasmonic sensor in combination with ORD condition leads to substantially enhanced sensing performance and has been explored for the first time to the best of our knowledge.

Monolithic VECSEL for stable kHz linewidth.

Vertical-external-cavity surface-emitting semiconductor lasers (VECSELs) are of increasing interest for applications requiring ultra-coherence and/or low noise at novel wavelengths; performance that is currently achieved via high-Q, air-spaced resonators to achieve long intra-cavity photon lifetimes (for the so-called class-A low noise regime), power scaling and high beam quality. Here, we report on the development of a compact, electronically tunable, monolithic-cavity, class-A VECSEL (monolithic VECSEL) for ultra-narrow free-running linewidths. A multi-quantum-well, resonant periodic gain structure with integrated distributed Bragg reflector (DBR) was optically-bonded to an air-gap-free laser resonator created inside a right-angle fused-silica prism to suppress the influence of environmental noise on the external laser oscillation, thus achieving high stability. Mode-hop-free wavelength tuning is performed via the stabilized temperature; or electronically, and with low latency, via a shear piezo-electric transducer mounted on the top of the prism. The free-running linewidth, estimated via the frequency power spectral density (PSD), is sub-kHz over ms timescales and <1.9 kHz for time sampling as long as 1s, demonstrating at least two orders-of-magnitude improvement in noise performance compared to previously reported single frequency VECSELs. The stable, total internal reflection resonator concept is akin to the prevalent monolithic non-planar ring oscillator (NPRO), however the monolithic VECSEL has several important advantages: tailored emission wavelength (via semiconductor bandgap engineering), no relaxation oscillations, no applied magnetic field, and low requirements on the pump beam quality. This approach is power-scalable in principle and could be applied to VECSELs at any of the wavelengths from the visible to the mid-infrared at which they are already available, to create a range of robust, ultra-coherent laser systems with reduced bulkiness and complexity. This is of particular interest for remote metrology and the translation of quantum technologies, such as optical clocks, from research laboratories into real world applications.

Quasi-achromatic rhomb compensator: Mueller matrix analysis versus azimuthal angle

A quasi-achromatic rhomb compensator has been developed to address shortcomings of the bi-plate compensator in rotating compensator spectroscopic ellipsometry (SE) and consequently to improve the accuracy of such measurements over broad spectral ranges. The compensator implemented here is based on a three-reflection in-line design comparable to that put forth by Krasilov in 1963, but altered for greater simplicity. Our design consists of 30°-60°-90° and 60°-60°-60° fused silica prisms in physical contact that generate total first and third internal reflections from their interfaces to the ambient. The 30°-60°-90° prism also generates the second internal reflection via an aluminum coating on the longer side opposite the hypotenuse. Prior to implementing the compensator as the rotating element of a SE instrument, its performance has been characterized versus azimuthal angle over the photon energy range from 1.2 eV to 5.4 eV. For this purpose, the compensator was aligned on a rotatable mount and its complete Mueller matrix was measured at selected azimuthal angles. We present an analysis of ψ for the aluminum coating, which generates a compensator dichroic angle ψC deviating from the ideal value of 45° by values ranging from 0.3° to 1.2° with increasing photon energy. This analysis also predicts a (fused silica)/Al interface contribution to the retardance of ∼ 176° to ∼ 160°. In addition, we present an analysis of the fused silica stress-induced deviations of the measured Mueller matrices from their ideal forms, the latter based on a dichroic compensator oriented at different azimuthal angles. The results of these analyses are expressions for the Mueller matrix elements which must be applied as functions of angle in order to completely characterize the polarization modifying properties of the device in rotating compensator instrument configurations.

Continuous-wave and SESAM mode-locked operation of the Yb:Bi4Si3O12 laser.

We demonstrate a comprehensive characterization of the diode-pumped Yb:Bi4Si3O12 laser operating in the continuous-wave and soliton mode-locked regimes. Pumping with a 650 mW, single-transverse mode, fiber-coupled laser diode, a maximum continuous-wave output power amounted to 213 mW with a slope efficiency up to 57.6%. A broadband wavelength tuning range of more than 70 nm was achieved in CW regime with a fused silica prism. Applying a SESAM as mode locker, nearly transform-limited pulses as short as 113 fs were generated for a maximum average power of 53 mW and a pulse repetition rate of ∼106 MHz. To the best of our knowledge, this is the first report on passively mode-locked operation with the Yb:Bi4Si3O12 crystal.

Evanescent coupling to silicon waveguides using surface plasmon polaritons.

In this work, we discuss evanescent light coupling to silicon waveguides using surface plasmon polaritons (SPPs) in the Otto configuration. The setup for excitation of SPPs includes a fused-silica prism, a 100nm silver layer with a 650nm airgap between them, and a tapered silicon waveguide located across from the silver layer. A $p$p-polarized light of 1550nm wavelength is incident at plasmonic angle of 44° to the interface of the fused silica-airgap to excite the SPP.A 2D Lumerical FDTD Solutions simulation shows a coupling efficiency of 54%. The fabricated device on a silicon-on-insulator substrate shows 10% light transmission for $p$p-polarized light.

Sub-10-fs pulse generation from a blue laser-diode-pumped Ti:sapphire oscillator

Pulses as short as 8.1 fs were generated from a blue laser-diode-pumped Kerr-lens mode-locked Ti:sapphire oscillator, with an average power of 27 mW and a repetition rate of 120.6 MHz. The full width at half-maximum exceeds 146 nm, benefitting from the dispersion management by a combination of a low-dispersion fused silica prism pair and a series of double-chirped mirrors. To the best of our knowledge, this is the first time to generate sub-10-fs pulses from a laser diode directly pumped Ti:sapphire oscillator.

Optical constants of iron and nickel metal and an assessment of their relative influences on silicate mixture spectra from the FUV to the NIR

We report new measurements of the optical constants of iron and nickel metal in the ultraviolet, visible, and near-infrared portions of the electromagnetic spectrum (∼0.16–3.59 µm), building upon the measurements of Cahill et al. (2012). These values were determined from metal films vapor-deposited onto fused-silica prisms. Our measurement of optical constants employed ellipsometry performed within the prism, sensing the side of the metal film unexposed to the ambient atmosphere. The data we report have important implications for modeling planetary reflectance and emittance spectra, especially in relation to space-weathering effects observed in remotely sensed data for the surfaces of the Moon, Mercury, and asteroids.

Sensing adsorption kinetics through slip velocity measurements of polymer melts.

The evolution over time of the nonlinear slip behavior of a polydimethylsiloxane (PDMS) polymer melt on a weakly adsorbing surface made of short non-entangled PDMS chains densely end-grafted to the surface of a fused silica prism has been measured. The critical shear rate at which the melt enters the nonlinear slip regime has been shown to increase with time. The adsorption kinetics of the melt on the same surface has been determined independently using ellipsometry. We show that the evolution of slip can be explained by the slow adsorption of melt chains using the Brochard-de Gennes's model.

Second-order interferometric autocorrelation for measuring group velocity dispersion and pulse broadening of femtosecond pulses.

Femtosecond pulse broadening and group velocity dispersion (GVD) were measured using a second-order interferometric autocorrelation technique. Two reference laser pulses of 36fs and 55fs were generated first in a Ti:sapphire oscillator and then passed through the optical elements of Ti:sapphire crystal and BK7 and fused silica glasses. For rectangular Ti:sapphire crystal and BK7 and fused silica slabs, material dispersion, and for fused silica prisms, material as well as angular dispersions were systematically measured. The experimental results were then compared with theoretical models, showing excellent agreement. The result of this work shows that one can rely very well on theoretical expressions to calculate the GVD of materials mentioned in this work and femtosecond pulse broadening.

The PANDA Barrel DIRC

The PANDA experiment at the international accelerator Facility for Antiproton and Ion Research in Europe (FAIR) near GSI, Darmstadt, Germany will address fundamental questions of hadron physics. Excellent Particle Identification (PID) over a large range of solid angles and particle momenta will be essential to meet the objectives of the rich physics program. Charged PID for the barrel region of the PANDA target spectrometer will be provided by a DIRC (Detection of Internally Reflected Cherenkov light) detector. The Barrel DIRC will cover the polar angle range of 22̂–140̂ and cleanly separate charged pions from kaons for momenta between 0.5 GeV/c and 3.5 GeV/c with a separation power of at least 3 standard deviations. The design is based on the successful BABAR DIRC and the SuperB FDIRC R&D with several important improvements to optimize the performance for PANDA, such as a focusing lens system, fast timing, a compact fused silica prism as expansion region, and lifetime-enhanced Microchannel-Plate PMTs for photon detection. This article describes the technical design of the PANDA Barrel DIRC and the result of the design validation using a “vertical slice” prototype in hadronic particle beams at the CERN PS.

Invited Article: An active terahertz polarization converter employing vanadium dioxide and a metal wire grating in total internal reflection geometry

Active broadband terahertz (THz) polarization manipulation devices are challenging to realize, but also of great demand in broadband terahertz systems. Vanadium dioxide (VO2) shows a promising phase transition for active control of THz waves and provides broadband polarization characteristics when integrated within grating-type structures. We creatively combine a VO2-based grating structure with a total internal reflection (TIR) geometry providing a novel interaction mechanism between the electromagnetic waves and the device, to realize a powerful active broadband THz polarization-controlling device. The device is based on a Si-substrate coated with a VO2 layer and a metal grating structure on top, attached to a prism for generating the TIR condition on the Si-VO2-grating interface. The grating is connected to electrodes for electrically switching the VO2 between its insulating and conducting phases. By properly selecting the incident angle of the THz waves, the grating direction, and the incident polarization state, we first achieved a broadband intensity modulator under a fused silica prism with an average modulation depth of 99.75% in the 0.2-1.1 THz region. Additionally, we realized an active ultra-broadband quarter-wave converter under a Si prism that can be switched between a 45° linear rotator and a quarter wave converter in the 0.8-1.5 THz region. This is the first demonstration of an active quarter-wave converter with ultra-broad bandwidth performance. Our work shows a highly flexible and multifunctional polarization-controlling device for broadband THz applications.

A High-Pulse-Energy High-Beam-Quality Tunable Ti:Sapphire Laser Using a Prism-Dispersion Cavity**Supported by the National Natural Science Foundation of China under Grant Nos 61275157 and 61475040, the National Key Scientific Instrument and Equipment Development Project under Grant No 2012YQ120048, the National Development Project for Major Scientific Research Facility under Grant No ZDYZ2012-2, and the National Key Research and Development Program of China

A high-pulse-energy high-beam-quality tunable Ti:sapphire laser pumped by a frequency-doubled Nd:YAG laser is demonstrated. Using a fused-silica prism as the dispersion element, a tuning range of 740–855 nm is obtained. At an incident pump energy of 774 mJ, the maximum output energy of 104 mJ at 790 nm with a pulse width of 100 μs is achieved at a repetition rate of 5 Hz. To the best of our knowledge, it is the highest pulse energy at 790 nm with pulse width of hundred micro-seconds for an all-solid-state laser. The linewidth of output is 0.5 nm, and the beam quality factor M2 is 1.16. The high-pulse-energy high-beam-quality tunable Ti:sapphire laser in the range of 740–855 nm can be used to establish a more accurate and consistent absolute scale of second-order optical-nonlinear coefficients for KBe2BO3F2 measured in a wider wavelength range and to assess Miller’s rule quantitatively.

Crystal growth, spectroscopic characterization, and sub-100 femtosecond mode-locked operation of a Yb:LiLuF_4 laser

We present a comprehensive growth, spectroscopic, and laser performance investigation of a Yb:LiLuF4 crystal, including CW laser experiments, and, for the first time to the best of our knowledge, mode-locked laser operation. Pumping with two 400 mW, polarization-combined, single-mode fiber-coupled laser diodes, we demonstrated efficient CW emission with 140 mW maximum output power and up to 59% slope efficiency. Using a semiconductor saturable absorber mirror for inducing the mode-locked regime and a pair of fused silica prisms for intracavity group delay dispersion compensation, we obtained soliton mode-locking pulses with 90 fs duration for the emission with polarization parallel to the crystal c-axis and 113 fs for the orthogonal polarization, with average power exceeding 30 mW in both cases at about a 90 MHz repetition rate.

Holography with a neutron interferometer.

We use a Mach-Zehnder interferometer to perform neutron holography of a spiral phase plate. The object beam passes through a spiral phase plate, acquiring the phase twist characteristic of orbital angular momentum states. The reference beam passes through a fused silica prism, acquiring a linear phase gradient. The resulting hologram is a fork dislocation image, which could be used to reconstruct neutron beams with various orbital angular momenta. This work paves the way for novel applications of neutron holography, diffraction and imaging.

Photoluminescence excitation of lithium fluoride films by surface plasmon resonance in Kretschmann configuration

We report on excitation of the photoluminescence of lithium fluoride by means of the surface plasmon resonance of Al layer. Advantage of this method is high efficiency of the excitation, which is applicable to ultra-thin films. P-polarized UV diode laser light is coupled to the surface plasmon resonance using a fused silica prism in Kretschmann configuration. The angular dependence of the reflected intensity is measured using a theta–2theta goniometer. The surface plasmon at resonance condition induces photoluminescence in the adjacent lithium fluoride layer. The fluoride layers were deposited on Al-coated fused silica substrates by electron beam evaporation. For the experiment, we prepared several samples with thickness ranging from 20 to 71 nm. We studied the effect of the luminescence enhancement by the surface plasmon resonance effect. Strong quenching effect was observed in the thinnest LiF layer. Influence of X-ray irradiation on the photoluminescence was studied.

High-energy infrared femtosecond pulses generated by dual-chirped optical parametric amplification.

We demonstrate high-energy infrared femtosecond pulse generation by a dual-chirped optical parametric amplification (DC-OPA) scheme [Opt. Express19, 7190 (2011)]. By employing a 100 mJ pump laser, a signal pulse energy exceeding 20 mJ at a wavelength of 1.4 μm was achieved before dispersion compensation. A total output energy of 33 mJ was recorded. Under a further energy scaling condition, the signal pulse was compressed to an almost transform-limited duration of 27 fs using a fused silica prism compressor. Since the DC-OPA scheme is efficient and energy scalable, design parameters for obtaining 100 mJ level infrared pulses are presented, which are suitable as driver lasers for the energy scaling of high-order harmonic generation with sub-keV photon energy.

Water structure at the interfaces between a zwitterionic self-assembled monolayer/liquid water evaluated by sum-frequency generation spectroscopy

A silane coupling agent having a zwitterionic end group was covalently bound to a semi-cylindrical fused silica prism for sum-frequency generation (SFG) analyses and to a flat glass for estimating biological affinity. It was found that total intensity of the OH stretching region (3000–3600cm−1) of the SFG spectrum derived from water in contact with a zwitterionic SAM-modified surface was smaller than that of SFG spectra derived from water in contact with a positively or negatively charged SAM-modified surface and a bare silica prism. These results indicated that water molecules in the vicinity of the zwitterionic SAM-modified surface are not strongly oriented in comparison with those of lopsidedly charged SAMs and bare silica. Moreover, the zwitterionic SAM surface suppressed non-specific adsorption of bovine serum albumin in contrast to the significant adsorption to lopsidedly charged SAMs and the bare cover glass. On the other hand, fibroblasts gradually adhered to the SAM surfaces and extended regardless of the electrical charge of the SAM, though the number of cells that adhered to the zwitterionic SAM was the smallest. The results strongly suggested that the charge neutralization of a solid material surface is very important for anti-biofouling properties.

High-efficiency fused-silica reflection grism

A fused-silica reflection grism (combination of grating and prism) based on the phenomenon of total internal reflection (TIR), and used in the -1st order, is designed and fabricated. The grism is etched directly into the fused-silica prism, which greatly facilitates the use of the TIR grating as no other angle coupling devices are involved. The grating profile is optimized by the use of the rigorous coupled-wave analysis method. Diffraction efficiency of larger than 99% at a wavelength of 980 nm for TM-polarized waves can be theoretically obtained. Two-beam interference lithography and inductively coupled plasma etching techniques are used to manufacture such grism. Diffraction efficiencies of larger than 95% are experimentally demonstrated.

Resonance, multiple diffusion and critical tunneling for Gaussian lasers

We present a detailed study of the gaussian laser propagation through a dielectric system composed by two right angle prisms. We investigate the transition between the spatial coherence limit, which exhibits wave-like properties and for which the resonance phenomenon can be seen, and the decoherence limit, which exhibits particle-like properties and for which the multiple diffusion occurs. We also analyze the tunneling at critical angles. In our numerical analysis, we shall use BK7 and Fused Silica prisms and a gaussian He-Ne laser with a wavelength of 632.8 nm and beam waists of 2 mm and 200 micron.

Sensitivity enhancement for evanescent-wave sensing using cavity-ring-down ellipsometry

We demonstrate a method to increase the sensitivity of the s-p phase shift under total internal reflection (TIR) for optical sensing. This is achieved by the introduction of two simple dielectric layers to the TIR surface of a fused silica prism. The enhanced sensitivity is demonstrated using evanescent-wave cavity-ring-down-ellipsometry by measuring the refractive index of liquid mixtures and by studying the adsorption of polymers to the TIR surface of the fused silica prism.