Compact Cavity Research Articles

Compact, diode-side-pumped and Q-switched Nd:YLiF4 laser cavity operating at 1053 nm with diffraction limited beam quality

This work reports a diode-side-pumped and passively Q-switched Nd:YLiF4 (YLF) laser operating at 1053 nm using a new laser resonator concept. Very stable pulses of 1 mJ energy with less than 10 ns pulse duration are obtained at 1 kHz repetition rate in a very simple, compact, and robust cavity that uses a double bounce configuration to achieve TEM00 operation.

Planar-waveguide external cavity laser stabilization for an optical link with 10-19 frequency stability

We stabilized the frequency of a compact planar-waveguide external cavity laser (ECL) on a Fabry-Perot cavity (FPC) through a Pound-Drever-Hall scheme. The residual frequency stability of the ECL is 10(-14), comparable to the stability achievable with a fiber laser (FL) locked to an FPC through the same scheme. We set up an optical link of 100 km, based on fiber spools, that reaches 10(-19) relative stability, and we show that its performances using the ECL or FL are comparable. Thus ECLs could serve as an excellent replacement for FLs in optical links where cost-effectiveness and robustness are important considerations.

Narrow-line-width 131-μm wavelength tunable quantum dot laser using sandwiched sub-nano separator growth technique

A wide wavelength tunable quantum dot (QD) external cavity laser operating in the 1.31-μm waveband with a narrow line-width is successfully demonstrated. A high-density, high-quality InAs/InGaAs QD optical gain medium for the 1.31-μm waveband was obtained using a sandwiched sub-nano separator growth technique. A wide wavelength tunability of 1.265-1.321 μm and a narrow line-width of 210 kHz were successfully achieved using a compact and robust external cavity system constructed with multiple optical band-pass and etalon filters for active optical mode selection. The laser also achieved an error-free 10-Gb/s photonic data transmission over an 11.4-km-long holey fiber.

Excitability in a semiconductor laser with saturable absorber

We show that a monolithic and compact vertical cavity laser with intracavity saturable absorber can emit short excitable pulses. These calibrated optical pulses can be excited as a response to an input perturbation whose amplitude is above a certain threshold. Subnanosecond excitable response is promising for applications to novel all-optical devices for information processing or logical gates.

2 μm passive Q-switched mode-locked Tm 3+:YAP laser with single-walled carbon nanotube absorber

We report the first demonstration, to our knowledge, of passive Q-switched mode-locking in a Tm 3+:YAP laser, operating in the 2 μm broadly spectral region formed with a compact Z-flod cavity. A transmission-type single-walled carbon nanotube saturable absorber (SWCNT–SA) is used for the initiation of the pulse generation. The repetition rate of the Q-switched envelope was 60 kHz at the pump power of 8.6 W. The mode-locked pulses inside the Q-switched pulse envelope had a repetition rate of ∼92 MHz. A maximum average output power of 761 mW was obtained. The dependence of the operational parameters on the pump power was also investigated experimentally.

High efficiency continuous-wave single-frequency Nd:YVO4 ring laser under diode pumping at 880 nm

An efficient single-frequency continuous-wave Nd:YVO4 ring laser pumped at 880 nm is presented. With compact four-mirror ring cavity and optical isolator, we obtained an output power of 14.56 W at 1064 nm, corresponding to a slope efficiency of 61.7% and an optical-to-optical efficiency of 58.4% with respect to the absorbed pump power. The stability of the output power was better than ±0.5% over two hours. At the same time, a beam quality factor of M 2≈1.2 was measured and the line width of the longitudinal mode was about 25 MHz. To the best of our knowledge, this is the highest slope efficiency and optical-to-optical efficiency in single-frequency Nd:YVO4 ring laser.

A Compact Diode Laser Cavity Ring-Down Spectrometer for Atmospheric Measurements of NO<SUB>3</SUB> and N<SUB>2</SUB>O<SUB>5</SUB> with Automated Zeroing and Calibration

A compact rack-mounted cavity ring-down spectrometer (CRDS) for simultaneous measurements of the nocturnal nitrogen oxides NO(3) and N(2)O(5) in ambient air is described. The instrument uses a red diode laser to quantify mixing ratios of NO(3) (at its absorption maximum at 662 nm) and of N(2)O(5) following its thermal dissociation to NO(3) in a second detection channel. The spectrometer is equipped with an automated zeroing and calibration setup to determine effective NO(3) absorption cross-sections and NO(3) and N(2)O(5) inlet transmission efficiencies. The instrument response was calibrated using simultaneous measurements of NO(2), generated by thermal dissociation of N(2)O(5) and/or by titration of NO(3) with excess NO, using blue diode laser CRDS at 405 nm. When measuring ambient air, the (2σ, 10 s) precision of the red diode CRDS varied between 5 and 8 parts-per-trillion by volume (pptv), which sufficed to quantify N(2)O(5) concentrations under moderately polluted conditions. Sample N(2)O(5) measurements made on a rooftop on the University of Calgary campus in August 2010 are presented. A maximum N(2)O(5) mixing ratio of 130 pptv was observed, corresponding to a steady-state lifetime of less than 50 min. The NO(3) mixing ratios were below the detection limit, consistent with their predicted values based on equilibrium calculations. During the measurement period, the instrument response for N(2)O(5) was 70% of the theoretical maximum, rationalized by a slight mismatch of the laser diode output with the NO(3) absorption line and a N(2)O(5) inlet transmission efficiency less than unity. Advantages and limitations of the instrument's compact design are discussed.

Flow-acoustic Characterisation of a Cavity-based Combustor Configuration

This study concerns the flow-acoustic characterisation of a cavity-based combustor configuration. A well-validated numerical tool has been used to simulate the unsteady, two-dimensional reacting flow. Initially, a conventional flow over a cavity with dimensions and conditions corresponding to a compact cavity combustor was studied. Cavity mass injections in the form of fuel and air injections required for trapped vortex formation were then employed and the resonance features of this configuration were studied. The results indicate that the cavity depth mode resonance mechanism is dominant at the conditions studied in this work and that the oscillation frequencies do not change with cavity air injection. This observation is important since it implies that the only important variable which can alter resonant frequencies is the cavity depth. With combustion, the pressure oscillation amplitude was observed to increases significantly due to periodic entrainment of the cavity air jet and fluctuation of fuel-air mixture composition to produce highly fluctuating heat-release rates. The underlying mechanisms of the unsteady flow in the cavity combustor identified in this study indicate the strong dependence of the acoustics on the cavity injection strategies.

Diode-pumped acousto-optically Q-switched high-repetition-rate Nd:YAG lasers at 946 and 473 nm by intracavity frequency-doubling

A diode-pumped acousto-optically (AO) Q-switched high-repetition-rate Nd:YAG lasers at 946 and 473 nm by intracavity frequency-doubling were reported in this paper. Using a compact V-type laser cavity, a maximum average output power of 4.5 W 946 nm laser was obtained at an operating repetition rate of 10 kHz, corresponding to an optical conversion efficiency of 10.5% and a slope efficiency of 15.6%. With a BiBO crystal as the intracavity frequency-doubler, 1.35 W 473 nm pulsed laser was achieved at 10 kHz. The peak power of the Q-switched blue pulse was up to 4.1 kW, with a pulse width of 33.1 ns. Then, the long-term power instability was less than 1%. Moreover, stable pulsed operation of 946 nm and 473 nm lasers can even reach 50 kHz.

Biochemical Studies and Ligand-bound Structures of Biphenyl Dehydrogenase from Pandoraea pnomenusa Strain B-356 Reveal a Basis for Broad Specificity of the Enzyme

Biphenyl dehydrogenase, a member of short-chain dehydrogenase/reductase enzymes, catalyzes the second step of the biphenyl/polychlorinated biphenyls catabolic pathway in bacteria. To understand the molecular basis for the broad substrate specificity of Pandoraea pnomenusa strain B-356 biphenyl dehydrogenase (BphB(B-356)), the crystal structures of the apo-enzyme, the binary complex with NAD(+), and the ternary complexes with NAD(+)-2,3-dihydroxybiphenyl and NAD(+)-4,4'-dihydroxybiphenyl were determined at 2.2-, 2.5-, 2.4-, and 2.1-Å resolutions, respectively. A crystal structure representing an intermediate state of the enzyme was also obtained in which the substrate binding loop was ordered as compared with the apo and binary forms but it was displaced significantly with respect to the ternary structures. These five structures reveal that the substrate binding loop is highly mobile and that its conformation changes during ligand binding, starting from a disorganized loop in the apo state to a well organized loop structure in the ligand-bound form. Conformational changes are induced during ligand binding; forming a well defined cavity to accommodate a wide variety of substrates. This explains the biochemical data that shows BphB(B-356) converts the dihydrodiol metabolites of 3,3'-dichlorobiphenyl, 2,4,4'-trichlorobiphenyl, and 2,6-dichlorobiphenyl to their respective dihydroxy metabolites. For the first time, a combination of structural, biochemical, and molecular docking studies of BphB(B-356) elucidate the unique ability of the enzyme to transform the cis-dihydrodiols of double meta-, para-, and ortho-substituted chlorobiphenyls.

In-fiber Mach–Zehnder interferometer formed by large lateral offset fusion splicing for gases refractive index measurement with high sensitivity

A versatile, compact and sensitive in-fiber open cavity Mach–Zehnder interferometer (MZI) gas refractive index (RI) sensor formed by fusion splicing a short section of single-mode fiber (SMF) between two sections of single-mode fibers with a large intentional lateral offset is demonstrated. The fabrication is easy, safe, and cost effective. Gas or other materials can contact with the light signal in the totally open cavity of sensor directly and easily, thus the ambient refractive index (RI) change can be detected very quickly. We discussed the fabrication and operation of the sensor, and we successfully used the sensor to monitor changes of refractive index of air as a function of pressure and obtained a sensitivity of over 3402 nm/RIU (refractive index unit) with good linearity and repeatability.

Development of a wideband compact leaky wave cavity antenna

As operating frequencies decrease, the aperture size of leaky wave antennas increases significantly – rendering them unsuitable for many sophisticated applications requiring small-sized communication antennas. In this article, a compact leaky wave cavity antenna with wide impedance bandwidth, using tapered cavity with substrate integrated waveguide is proposed. The antenna consists of a substrate and a rectangular metallic cavity fed by an L-shaped feed element. The metallic strips are placed along the sides of the substrate to fabricate a substrate integrated waveguide. The cavity is tapered to steer the beam in the desired direction. The tapering of the cavity causes the placement of the L-shaped feed element near the back wall of the cavity, producing input impedance mismatching. This problem of input impedance mismatching is resolved by the substrate integrated waveguide. It is demonstrated that the proposed antenna is compact (2λ0), and is wideband with voltage standing wave ratio (VSWR) bandwidth of 24% for 2:1 VSWR and a gain of 8.4 dBi. The experimental results for the designed antenna are in close agreement with the simulation results. The proposed antenna can be utilized in different wireless applications such as mobile communications, road vehicle communications and other applications.

Auditory and vestibular impairment of Slitrk6-Deficient mice

A diode pumped Tm3+ doped YAlO3 (Tm:YAP ) self-Q-switched near 2 μm laser was studied with a compact linear cavity. Stable self-Q-switched laser pulses were obtained at the central wavelength of 1988 nm with the maximum average output power of 1.68 W, corresponding to the slope efficiency of 31.7%. The pulse repetition rate and single pulse energy were 65.16 kHz and 25.7 μJ, respectively. To the best of our knowledge, this is the first demonstration of a diode pumped all-solid-state self-Q-switched laser at the 2 μm region.

Controlling the Stereospecificity of a Volume-Conserving Adiabatic Photoisomerization within a Nanotubular Self-Assembled Cage: A Reversible Light–Heat Torque Converter

We present herein a host-guest supramolecular system by which we were able to obtain precise control of the stereospecificity of a new and unusual adiabatic photoisomerization reaction capable of restoring reversibly the original configuration. The host-guest system is composed of (a) a naphthalene ring linked centrosymmetrically-via sp(2) hybridized oxygen atoms-with methoxytriethyleneglycol chains (1) and (b) a nanotubular cage formed by four self-assembled face-to-face β-cyclodextrins threaded onto the long "axle" of 1. The compound 1 can exist in distinct cis,cis, cis,trans, and trans,trans conformations that are spectrally distinguishable (see Scheme 1 ). Spectroscopic and kinetic manifestations of the torsional isomerization of 1 in the lowest excited singlet state both in solution and within the tubular cage were investigated. The results provide clear evidence that the compact cavity completely blocks the photoisomerization pathway manifested in common solution (cis,cis* → cis,trans*), allowing observation of stereospecific, volume-conserving turning of the naphthalene ring about the two "quasidouble" bonds C(Naph)-O by φ ≈ 180° (cis,cis* → trans,trans*). The photoisomerization is purely adiabatic, and the encaged molecule restores its original configuration by generating torque thermally, when relaxing to the ground state.

Compact, 15 mJ, 450 MHz, CdSiP_2 picosecond optical parametric oscillator near 63 μm

We report a compact, efficient, high-energy, and high-repetition-rate mid-IR picosecond optical parametric oscillator (OPO) based on the new nonlinear material CdSiP(2) (CSP). The OPO is synchronously pumped by a master oscillator power amplifier system at 1064.1 nm, providing 1 μs long macropulses constituting 8.6 ps micropulses at 450 MHz, and it can be tuned over 486 nm across 6091-6577 nm, covering the technologically important wavelength range for surgical applications. Using a compact (∼30 cm) cavity and improved, high-quality nonlinear crystal, idler macropulse energy as high as 1.5 mJ has been obtained at 6275 nm at a photon conversion efficiency of 29.5%, with >1.2 mJ over more than 68% of the tuning range, for an input macropulse energy of 30 mJ. Both the signal and idler beams are recorded to have good beam quality with a Gaussian spatial profile, and the extracted signal pulses are measured to have durations of 10.6 ps. Further, from the experimentally measured transmission data at 1064 nm, we have estimated the two-photon absorption coefficient of CSP to be β=2.4 cm/GW, with a corresponding energy bandgap, E(g)=2.08 eV.

High-performance laser-pumped rubidium frequency standard for satellite navigation

Presented is a double-resonance continuous-wave laser-pumped rubidium (Rb) atomic clock with a short-term stability of 4×10−13 τ−1/2 for integration times 1 s≤τ≤1000 s, and a medium- to long-term stability reaching the 1×10−14 level at 104 s. The clock uses an Rb vapour cell with increased diameter of 25 mm, accommodated inside a newly developed compact magnetron-type microwave cavity. This results in a bigger signal with reduced linewidth, and thus improved short-term stability from a clock with 1 dm3 physics package volume only. The medium- to long-term clock stability is achieved by minimising the effects of light-shift and temperature coefficient on the atoms. Potential applications of the clock are discussed.

A compact extended cavity laser using a micromachined silicon flexure for atomic spectroscopy

We report a novel compact extended cavity diode laser (ECDL) system for applications in atomic physics. It employs a 6.5 mm invar cavity, a volume holographic grating (VHG), and a micromachined silicon flexure integrated with a pair of piezoelectric transducer (PZT) actuators, and the overall laser system has a size of 26.3 mm × 20 mm × 20 mm. The advantages of using a silicon flexure are its high material rigidity and simple microfabrication process with designable displacement. The measured spring constant of the silicon flexure is 1.56 × 10 5 N/m, and its deflection is 157.45 nm. This displacement alters the laser cavity length, leading to a frequency tuning range of 9.31 GHz. A frequency tuning range of 11.6792 GHz can also be achieved by changing the VHG temperature, providing another fine tuning mechanism. The laser wavelength was swept between 780.2533 and 780.2344 nm, covering the rubidium D 2 absorption peaks.

Design of a compact quarter wave coaxial cavity resonator for plasma ignition applications

Atmospheric and higher pressure RF and microwave plasma sources have numerous applications including material processing and spectroscopy. More recently, advantages in using such discharges for combustion ignition are being investigated. A particularly simple and compact microwave discharge generating device is the quarter wave coaxial cavity resonator (QWCCR). This paper presents a new, compacted design of such a device. A simple approximate analysis of the quality factor, Q, which is a measure of the resonant electromagnetic potential step-up capability is given, and compared to experimentally measured quality factors showing reasonable agreement. Analytic results indicate that the foreshortened folded cavity quality factors are comparable to tapered coaxial cavity designs.

Graphene-Assisted Multiwavelength Erbium-Doped Fiber Ring Laser

We propose and experimentally demonstrate a stable multiwavelength erbium-doped fiber (EDF) ring laser based on four-wave-mixing of atomic few-layer graphene. The compact laser cavity consists of 3-m EDF, an optically deposited ultrathin graphene device, and a polarization-maintaining fiber Sagnac loop filter. The comparison between the ring laser cavity without and with the graphene device shows that the highly nonlinear graphene can be helpful to mitigate the mode competition of EDF laser and stabilize the multiwavelength oscillation. Under the assistance of the graphene device, power-equalized eleven-channel simultaneous lasing with a wavelength-spacing of 0.54 nm is achieved at room temperature. This laser has a very high extinction ratio up to 57 dB and a narrow linewidth per channel of less than 0.01 nm.

Study of a compact external magnetic field radial split-cavity oscillator

With the experiment result analyses of a coaxial virtual cathode oscillator (CVCO), a new kind of compact radial split cavity oscillator (RSCO) is presented in this paper. On the oscillator, a low resistance tube is formed by using the diode structure of a CVCO, and a radial split-cavity structure is formed by several meshes that cause the electronic beam to transmit. Calculating all kinds of parameter, at the input parameter 350 kV, 27 kA, the numerical simulation results show that the average output microwave power is about 4.0 GW, the microwave frequency is 1.37 GHz, and the electronic efficiency is 42.3%.