Plane-parallel Cavity Research Articles

A compact high power diode side-pumped 2.09 μm Tm,Ho:YAG laser

We demonstrate a high power compact continuous-wave diode side-pumped Tm,Ho:YAG all solid-state laser at room temperature. A high dopant concentration ratio of Tm,Ho:YAG (3 at.% Tm3+, 0.1 at.% Ho3+) crystal rod with laser diode (LD) side-pumped architecture is employed as a laser head. With a single laser head in a plane-parallel short cavity, a maximum 57 W output power is obtained at a temperature of 19 °C, corresponding to an optical-to-optical efficiency of 10.6% and a slope efficiency of 16.6%. To the best of our knowledge, this is the highest output power of LD-pumped Tm,Ho co-doped laser operating at room temperature. This laser system also exhibits excellent power stability in 90 min, making it widely applicable in various fields.

Unbiased Glucose Biosensing Based on a Schottky Junction Comprised of Au Nanoparticle-Decorated TiO2-Coated Al Films

Photoelectrochemical (PEC) biosensors show great potential in biochemical molecular detection due to the advantages of low background noise, high sensitivity, and easy integration. However, the current PEC glucose biosensors are subject to the deficiencies of the relatively large limit of detection, small detectable range of concentration, and requirement of an operation voltage. Herein, we construct an unbiased glucose biosensor both in three- and two-electrode configurations using a glucose oxidase (GOx)-modified Schottky junction comprised of Au nanoparticle (NP)-decorated TiO2-coated Al films. A wide detectable range of concentration (0.3–104 μM) is achieved at relatively zero bias versus the reference electrode in a three-electrode configuration under AM 1.5G illumination along with a fitted sensitivity of 3780 μA mM–1 cm–2 (in the concentration range of 0.3–1.0 μM) and a limit of detection down to 0.05 μM. The photocurrents corresponding to typical interfering substances (e.g., uric acid and ascorbic acid) are less than 10% of that to glucose. Moreover, the constructed sensor achieves almost no attenuation in photocurrent under light ON/OFF circular irradiation for 30 min and shows a photocurrent around 92% of the initial value after 30-day storage in air at room temperature. The satisfactory sensing performance is ascribed to the following three aspects: (1) the optical absorption is enhanced due to the formation of a plane-parallel resonance cavity and the reduced band gap of the TiO2 material, (2) the separation and extraction of the photogenerated carriers are facilitated due to the Al doping and the embedded Schottky junction, and (3) the carrier transfer from the photoelectrode surfaces into the electrolyte is boosted because of the Au NPs and nanostructured GOx decoration. This work provides an alternative route to prepare high-performance and self-powered glucose sensors for diabetes diagnosis.

100 Hz repetition-rate 2.794 μm Cr,Er:YSGG passively Q-switched laser with Fe2+:ZnSe saturable absorber

A concave-convex resonator was used to compensate for the thermal focal length, which obviously realizes the high energy output of Cr,Er:YSGG lasers at 100 Hz pumped by a flash lamp. The maximum output energy of the concave-convex cavity is 62.3 mJ, which is 2.9 times the maximum with a plane-parallel cavity when the same energy is injected in free-running operation. A passively Q-switched 2.794 μm laser using a Fe2+:ZnSe saturable absorber was demonstrated in this research. The device produced single pulses of 4.3 mJ energy with a 107.6 ns pulse width and multi-pulses (5 pulses) with 20 mJ total output energy at 100 Hz.

Single-loss-modulated and dual-loss-modulated compact Nd:Gd3Ga5O12 lasers generating sub-nanosecond laser pulses

We report on a Nd:Gd3Ga5O12 crystal laser formed with a plane-parallel cavity, which could be passively Q-switched with single- or dual-loss modulation, and was capable of generating sub-nanosecond laser pulses. The laser was pumped by an 808-nm pulsed laser diode at a repetition rate of 120 Hz, with pump durations in a range of 100–350 μs. The shortest pulse width achieved in single-loss Q-switching was 461.7 ± 5.5 ps, and the highest peak power could amount to 128.5 ± 5.9 kW. Green laser pulses of 332 ps in width were also obtained through second-harmonic generation with a nonlinear component. In passively Q-switched operation with dual-loss modulation, the minimum pulse width attainable was 767.7 ± 2.5 ps, while the pulse peak power could reach 53.0 ± 6.6 kW.

Tunable 3 µm optical vortex parametric oscillator

We propose a tunable millijoule-level 3-µm vortex laser formed with a 1-µm ns vortex pulse-pumped quasi-phase matching MgO-doped periodically poled lithium niobate (MgO:PPLN) optical parametric oscillator with a singly resonant plane-parallel cavity configuration. The wavelength of the vortex output is tuned within the range of 3.360–3.677 µm merely by controlling the temperature of the MgO:PPLN crystal. The maximum vortex output energy of 2.14 mJ is obtained at the maximum pump energy of 21 mJ, and corresponds to an optical to optical conversion efficiency of 10.2% and a photon conversion efficiency of 33.5%. The handedness of the vortex output is controlled just by inverting the handedness of the pump vortex beam.

MODELING OF THE COMPRESSION OF WAVE PACKETS INDUCED BY A CURRENT FILAMENT IN A PLANE-PARALLEL WAVEGUIDE

The possibility of rigorous simulation of the compression of electromagnetic pulses excited by a filament with a current in a plane-parallel waveguide cavity is investigated. The technique of determining the modulation law of the pulses to be compressed, that has been developed in our previous papers, here is generalized to the case where the pulse source is an extraneous current. The process of compression is modeled with this technique for two symmetrical wave packets propagating towards each other in a ring-shaped waveguide. The interference of these packets is demonstrated in the performed numerical experiment. The result of the interference is doubling of the electric field intensity (regarding to the intensity in each separate wave packet) at the point of the waveguide which is diametrically opposed to that one where the external current is located. The obtained results could be used for the design of passive microwave power compressors and in the accelerator engineering.

Plate-shaped Yb:LuPO4 crystal for efficient CW and passively Q-switched microchip lasers

It is demonstrated that plate-shaped crystals of Yb:LuPO4, which are grown from spontaneous nucleation by high-temperature solution method, can be utilized to make microchip lasers operating in continuous-wave (CW) or passively Q-switched mode. Efficient operation of such a microchip laser, which is built with a 0.3 mm thick crystal plate in a 2 mm long plane-parallel cavity, is realized at room temperature. With 2.37 W of pump power absorbed, 1.45 W of CW output power is generated with a slope efficiency of 73%. When passively Q-switched with a Cr4+:YAG crystal plate as saturable absorber, the laser produces a maximum pulsed output power of 0.53 W at 1013.3 nm, at a pulse repetition rate of 23.8 kHz, the resulting pulse energy, duration, and peak power are 22.3 μJ, 4.0 ns, and 5.6 kW, respectively.

Diode-pumped Q-switched Nd:YLF laser at 1313 nm

In this letter, we describe the operation of an end-pumped acousto-optic Q-switched Nd:YLF laser. According to the theoretical analysis and calculation for Nd:YLF crystal, the thermal focal length of σ-polarized laser is positive in plane-parallel resonator, while that of π-polarized laser is negative. Hence laser operation at σ-polarized 1313 nm should be stable in plane-parallel cavity. When absorbed pump power is 12.45 W and the pulse repetition frequency is 10 kHz, 3.1 W output laser at 1313 nm is achieved. As a result, the optical–optical conversion efficiency is 25.4 % and slope efficiency is 31.2 %, respectively.

Laser diode end-pumped continuous-wave laser operation at 1339 nm in Nd : GGG with nearly diffraction-limited beam quality

We report on the laser diode end-pumped continuous-wave laser operation of a Nd : GGG single crystal at 1339 nm in a plane parallel laser cavity configuration, for the first time to our knowledge. A simultaneous tri-wavelength laser at 1324, 1331 and 1337 nm is obtained at first with a maximum output power up to 1.66 W in a free-running laser operation with a slope efficiency of about 27.6% with respect to the absorbed pump power. By inserting a 0.1 mm glass etalon into the laser cavity and finely tilting it to a suitable angle, a single wavelength lasing at 1339 nm can be realized with a maximum output power of 0.58 W and slope efficiency of about 12.9%. The output power stability is simply estimated to be about 4.1% and the output beam quality is measured to be as near the diffraction limit as 1.33 and 1.16 in x and y directions, respectively.

Output characteristics of a singly-resonant optical parametric oscillator: Dependence on the variation of the signal and idler output coupling

Output characteristics of a double-pass singly-resonant optical parametric oscillator (SRO) resonant for both signal and idler waves are investigated as a function of reflectivity of the output coupler based on periodically poled Mg -doped stoichiometric LiTaO 3( PPMgSLT ) with a period of 32.7 μm. A configuration of plane-parallel two-mirror cavity is employed and the crystal surfaces are not coated. The SRO was pumped by a Nd :YAG laser which provides 85 ns-long-pulses with a repetition rate of 10 kHz. In our experiment, the wavelengths of signal and idler are 1.98 and 2.3 μm and the maximum available pump power is ~ 21 W. Maximum average powers (conversion efficiency) of the total, the signal and the idler are 12.2 W (59%), 7 W (34%) and 5.6 W (27%), respectively.

Compact High-Peak-Power End-Pumped AlGaInAs Eye-Safe Laser With a Heat-Spreader Diamond Coated as a Cavity Mirror

We report on a high-peak-power end-pumped AlGaInAs laser at 1.52 μm with a linear plane-parallel cavity. A high-reflective coated diamond is utilized not only as the heat spreader but also as the front mirror simultaneously to make the laser cavity to be extremely compact. The average output power and the corresponding peak power under this cavity configuration is found to be up to 2.58 and 516 W separately at a repetition rate of 100 kHz and a pump power of 12 W corresponding to a peak power of 2.4 kW. The experimental results assure the promising application of dielectric coated diamond as a multifunctional optics to fulfill a high performance and compact cavity design.

Spectra and broad-spectral laser operation of a disordered Nd:LiLa(MoO4)2 crystal

The crystal characteristics of a disordered Nd:LiLa(MoO4)2 laser crystal were investigated in detail, including its structure, absorption, emission and Raman scattering spectra. Laser operation, end-pumped by an 808 nm diode laser, has been demonstrated in both a concave-plano and plane-parallel resonator cavity. A broad-spectral dual-peak laser emission at 1061 nm and 1060 nm with a full width at half maximum of 2 nm was obtained in the experiment. A maximum output power of 267 mW was obtained in the concave-plano cavity. However, in the plane-parallel cavity, laser output of 381 mW was obtained, giving a slope efficiency of 14.5%. The results lay the groundwork for Raman, mode-locked and tunable laser applications generated by a Nd:LiLa(MoO4)2 laser crystal.

Diffraction loss analysis of a plane-parallel optical cavity with a phase step and a slit aperture

A model for calculating the round trip diffraction loss in a plane-mirror cavity with an intracavity phase step and an infinite slit aperture is developed. The round trip remaining intensity fraction for the low order transverse cavity modes can be calculated for any given location of the slit aperture and the phase step along the cavity and for any given phase delay on the phase step. The diffraction loss on the slit aperture is found to be a periodic function of the phase delay on the phase step. Transformation of the lasing spectrum emitted from a broadband pulsed dye laser on moving the phase step along the oscillator cavity is reproduced theoretically. The lasing spectrum affected by the phase step is interpreted as the wavelength dependence of the remaining intensity fraction for the principal transverse mode.

High Power Continuous-Wave Diode-End-Pumped 1.34-μm Nd:GdVO4 Laser

A high power cw all-solid-state 1.34-μm Nd:GdVO4 laser is experimentally demonstrated. With a diode-double-end-pumped configuration and a simple plane-parallel cavity, a maximum output power of 27.9W is obtained at incident pump power of 96 W, introducing a slope efficiency of 35.4%. To the best of our knowledge, this is the highest output power of diode-end-pumped 1.3-μm laser. With the experimental data, the thermal-stress-resistance figure of merit of Nd:GdVO4 crystal with 0.3 at% Nd3+ doped level is calculated to be larger than 9.94 W/cm.

26.3-W continuous-wave, diode-double-end-pumped all-solid-state Nd:GdVO 4 laser operating at 1.34 μm

A high-power continuous-wave (CW) all-solid-state Nd:GdVO 4 laser operating at 1.34 μm is reported here. The laser consists of a low doped level Nd:GdVO 4 crystal double-end-pumped by two high-power fiber-coupled diode lasers and a simple plane-parallel cavity. At an incident pump power of 88.8 W, a maximum CW output of 26.3 W at 1.34 μm is obtained with a slope efficiency of 33.7%. To the best of our knowledge, this is the highest output at 1.34 μm ever generated by diode-end-pumped all-solid-state lasers.

Comparative studies of eye-safe intracavity and extracavity optical parametric oscillators with an unstable telescopic cavity

We have experimentally studied the lasing characteristics of an eye-safe optical parametric oscillator (OPO) with an unstable telescopic cavity when it is placed inside (intracavity OPO) and outside (extracavity OPO) the plane-parallel cavity of a pulsed, nearly single-mode KGW:Nd pump laser. We used a KTP crystal as the nonlinear medium for the OPO. We have shown that the intracavity OPO has the higher lasing efficiency. We have observed that the distribution of nonlinear losses introduced by the intracavity OPO, nonuniform over the cavity cross section, leads to an increase in the diameter and divergence of the radiation beam from the pump laser and a dependence of its temporal lasing dynamics on the transverse beam coordinate. We propose a physical model qualitatively explaining the spatial and temporal lasing dynamics of a radiation source with an intracavity OPO. Both OPO versions generate beams of radiation with about the same divergence. When the KGW:Nd laser has an electrical pumping energy of 7.3 J and a cavity length of 77 cm, the intracavity OPO and the extracavity OPO emit pulses with energies of 14.5 mJ and 12.0 mJ and duration 18 nsec and 13 nsec respectively. The divergence of the eye-safe radiation (λ = 1.578 µm) at 86.5% of the total pulse energy is no greater than 5.5 mrad for an OPO output beam diameter of = 2 mm.

A new concept of focusing antennas using plane-parallel fabry-perot cavities with nonuniform mirrors

An original configuration of low-profile directive antennas is presented in V-band. The focusing effect is performed by a plane-parallel Fabry-Perot (FP) resonator illuminated by a printed antenna. Both reflecting mirrors are made of metal strip gratings. The dimensions of the strips and slots of the nonperiodic output mirror are much smaller than the working wavelength; they are computed locally so that this mirror behaves as a spherical equiphase surface. Theoretical and experimental results show that the radiation patterns are symmetric and have low sidelobes. The antenna directivity is controlled by the value of the synthesized radius of curvature, that is to say by the nonperiodic distribution of the metal strips. It typically varies between 15 and 23.5 dB at 60 GHz. This new radiating structure is much more compact than substrate lenses and is compatible with low-cost multilayer technologies at millimeter wave frequencies. This is a possible candidate for user mobile-stations of indoor broadband communication systems.

Near‐field coupling between a printed antenna and a Fabry Perot resonator: Experimental study of the radiation properties at millimeter wave frequencies

AbstractCompact focusing antennas, consisting of a Fabry–Perot (FP) cavity coupled to a printed source, are studied in the 60‐GHz band. Several configurations of antennas, including plane‐parallel or plano‐convex cavities excited by a patch antenna or an array, are considered and compared. In particular, their radiation characteristics are investigated experimentally as a function of the operating frequency and the thickness of the free‐space coupling region separating the primary radiator from the resonator. The optimum coupling conditions are also defined to maximize the efficiency and minimize the sidelobe level. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 438–443, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11084

Evolution of the beam quality factor for various active medium positions within a Gaussian cavity

A 2-m-long plane-parallel cavity with a Gaussian reflectivity mirror has been applied to a XeCl discharge chamber with a 35-cm-long active medium and the temporal evolution of the main parameters of the intracavity laser radiation after reflection on the Gaussian mirror, has been analysed for various active medium positions within the cavity. It is shown that in cavities of equal length and effective Fresnel number, the properties of the intracavity radiation are dependent on the Gaussian mirror distance from the active medium, since the onset of laser action. Indeed, it has been found that the beam quality factor M 2 reaches smaller values by setting the Gaussian mirror closer to the active medium. It is also shown that a theory formerly developed for the evolution of the parameters of Schell–Gauss model beams propagating in Gaussian-mirror cavities provides a satisfactory description of experimental results.

Bodies with heterogeneities: The case of sets of cracks

We consider the problem of the localization of a vibration process by a set of plane parallel cavities (cracks) described by the Griffith theory [1]. These types of heterogeneities are the most widespread objects accompanying stratified inhomogeneous geological structures including an imitator of breaks. They are widespread imperfections in materials with defects and also the main precursors of strength loss in structures, thus determining the onset of their brittle rupture.