Three-mirror Cavity Research Articles

Spatiotemporal theory of a gyrotron based on a three-mirror cavity

We present the quasi-analytical spatiotemporal theory of the resonant traveling-wave tube scheme of a gyrotron based on the transverse amplifications of the operating wave and on the use of a remote delayed feedback. The main idea is to implement a system with a dense spectrum of eigenmodes, which makes it possible to smoothly adjust the generation frequency by switching from mode to mode when the operating magnetic field changes. On the basis of a simple 2D three-mirror model, we show the possibility of achieving the stable single-frequency generation regime in this system if the excess of the operating current above the starting threshold is not too high. The mechanism of loss of stability of the single-frequency generation with an increase in operating current is also described.

Unstable confocal resonator with external flat semi-transparent mirror for additional feedback

Main characteristics (mode structure of power loss, divergence of resonant radiation) of a three-mirror laser cavity with additional feedback are theoretically studied in the Fresnel approximation on the basis of the Fox-Lee integral equation. The resonator consists of two spherical mirrors, which form an unstable confocal resonator, and a flat semi-transparent mirror, which is installed outside the reference unstable resonator perpendicular to its optical axis. The flat coupling mirror returns part of the radiation back inside the resonator. The level of additional feedback is determined by the reflection coefficient of the flat mirror and the position of the mirror along the optical axis of the resonator. Variation of these parameters makes it possible to control the transparency of the three-mirror resonator over a wide range, up to values close to zero. Results of this paper can be used in the development of high-power lasers with wide aperture (Fresnel numbers of ∼100) on the basis of low-gain active media.

Pulsed Parametric Oscillator Based on KTP Crystals with a Three-Mirror Ring Cavity: Numerical Simulation

Pulsed Parametric Oscillator Based on KTP Crystals with a Three-Mirror Ring Cavity: Numerical Simulation

Prospects for the Implementation of an Intense Source of Ultraviolet Radiation Based on a Gas-Discharge Plasma in a Quasi-Optical Cavity Excited by a Pulse of Terahertz Radiation

An electrodynamic system is described that provides the creation of an electromagnetic wave field of high intensity at a frequency of 1 THz due to a combination of accumulation in time and compression in space of a wave pulse coming from an electron cyclotron maser (gyrotron). This system is based on the use of a three-mirror cavity consisting of two focusing mirrors and one flat corrugated Bragg-type photonic structure providing coupling between the gyrotron wave pulse and the operating wave of the cavity. The aim of this work is to use a “spot” of the intense terahertz field inside the cavity to provide a point-like plasma discharge in a gas stream injected into this spot; such a discharge can be a source of extreme ultraviolet radiation.

Secondary Raman and Brillouin mode suppression in two- and three-mirror-cavity diamond Raman lasers.

We report an investigation into secondary mode suppression in single longitudinal mode (SLM) 1240 nm diamond Raman lasers. For a three-mirror V-shape standing-wave cavity incorporating an intra-cavity LBO crystal to suppress secondary modes, we achieved stable SLM output with a maximum output power of 11.7 W and a slope efficiency 34.9%. We quantify the level of χ(2) coupling necessary to suppress secondary modes including those generated by stimulated Brillouin scattering (SBS). It is found that SBS-generated modes often coincide with higher-order spatial modes in the beam profile and can be suppressed using an intracavity aperture. Using numerical calculations, it is shown that the probability for such higher-order spatial modes is higher for an apertureless V-cavity than in two-mirror cavities due its contrasting longitudinal mode-structure.

Unmanned airborne miniaturized pulsed CO2 laser with wavelength automatic tuning

This paper presents a miniaturized mechanically Q-switched pulsed CO2 laser with wavelength automatic tuning, which could be used in unmanned airborne lidar system. A three-mirror cavity structure with real focus in the cavity is designed to provide a stable resonator, which has short beam transit time for mechanically Q-switched laser. The matching relationship between the beam in the resonant cavity and the aperture of the optical chopper is experimentally studied, the CO2 laser pulse output with good waveform is obtained, and the wavelength automatic tuning is realized. The CO2 laser produces a maximum output peak power of 3.7 kW at 10.59 μm for pulse width of 350 ns, corresponding beam quality M2 of 1.75, and the laser weight is about 18 kg.

High stability in near-infrared spectroscopy: part 1, adapting clock techniques to optical feedback

Optical feedback is an efficient way to narrow and stabilise semi-conductor lasers. As a step forward for ultra-stable, yet highly tunable sources, we developed a new prototype of a three-mirror V-shaped optical cavity (VCOF). It is made of a precisely machined Zerodur spacer, that holds 3 optical contacted mirrors forming a high finesse V-shaped cavity. This arrangement allows the resonant light to be sent back to the seeding laser, triggering a drastic narrowing of the emission linewidth well below the cavity mode width without the need for high-bandwidth active electronic lock of the laser on the cavity. Low expansion material and precise temperature control of the reference cavity leads to a source with Hz level frequency drift and 70 Hz-level emission linewidth at 215 THz. We discuss the benefits of this new prototype compared to its predecessor for high-sensitivity cavity ring down spectroscopy (CRDS). To serve this purpose, the frequency stabilised laser was characterised on short, mid and long time scales, using a high finesse etalon, a self referenced optical frequency comb and a long term saturated CRDS absorption Lamb dip measurement on water.

Higher-order Hermite-Gauss modes for gravitational waves detection

As part of the research on thermal noise reduction in gravitational-wave detectors, we experimentally demonstrate the conversion of a fundamental ${\mathrm{TEM}}_{00}$ laser mode at 1064 nm to higher-order Hermite-Gaussian modes (HG) of arbitrary order via a commercially available liquid crystal spatial light modulator. We particularly studied the ${\mathrm{HG}}_{5,5}/{\mathrm{HG}}_{10,10}/{\mathrm{HG}}_{15,15}$ modes. A two-mirror plano-spherical cavity filters the higher-order modes spatially. We analyze the cleaned modes via a three-mirror diagnosis cavity and measure a mode purity of $96/93/78%$ and a conversion efficiency of $6.6%/3.7%/1.7%$, respectively. A full set of simulations and mathematical proofs are also presented which shows that (i) Hermite-Gauss modes resonate in a two-mirror cavity provided mirrors are properly angled with respect to the impinging mode, and (ii) Hermite-Gauss modes resonate in triangular cavities. Hence, higher-order Hermite-Gauss modes are compatible with ground-based gravitational-wave detectors' architecture and can be employed for the mitigation of mirror thermal noise for the third generation Einstein Telescope or Cosmic Explorer.

A new fiber self-mixing temperature sensor with phase compensation for harmonic vibrations

Abstract A new fiber temperature sensor is proposed based on dual-longitudinal mode laser self-mixing interference effect in a distributed Bragg reflector fiber laser. The temperature analytical model is established by use of the three-mirror cavity model and the interference superposition theory of the multi-longitudinal mode laser. It is indicated that this preferable model is sufficient to real-time track the change of the self-mixing signal waveform resulting from the ambient temperature variation by means of the phase compensation method and the waveform separation phenomena. Furthermore, the experimental measurements show that the relative error can be lower to 1.43% corresponding to 4.95 × 10-4 m/°C of the temperature sensitivity ranging from 20.14 to 46.02 °C. It has demonstrated that the measured results are in good consistent with the reference values, thereby which this sensor proves capable of measuring ambient temperature with high sensitivity and accuracy.

Tunable polymer dye laser pumped by two 513 nm diodes

We demonstrate a tunable solid-state polymer dye laser with quasi-longitudinal pumping by two green (λ = 513 nm) laser diodes. Tuning curves with a maximum efficiency of 13% were attained, using a plate of crystalline quartz (Lyot filter) for wavelength selection. In a three-mirror cavity with partial compensation of astigmatism, the total tuning range was 62 nm (from 545 nm to 607 nm) for pyrromethene dyes: PM567, PM580 and PM597. The best results were achieved with active elements based on Pyrromethene 580 laser dye in a mixture of polyvinyl butyral or a copolymer of butylmethacrylate and methacrylic acid (ratio 9:1) with the addition of 30% dibutylsebacinate as a plasticizer.

High power simultaneous dual-wavelength CW and passively-Q-switched laser operation of LD pumped Tm:YLF at 1.9 and 2.3 µm.

Simultaneous dual-wavelength laser oscillation of Tm:YLF at 1.9 and 2.3 µm were successfully realized. The three-mirror cavity was exploited to study dual-wavelength laser performance, which is formed by a shared input mirror and two independent output couplers for the two laser wavelengths. Under an absorbed pump power of 15.2 W, the maximum CW output powers of 5.49 W around 1908nm and 1.12 W around 2305 nm were simultaneously obtained, corresponding to a total optical-to-optical conversion efficiency of 43.5%. A Cr2+:ZnSe was further used to passively Q-switch the dual-wavelength laser, generating pulses with pulse widths of 554 ns at 1.9 µm and 4 µs at 2.3 µm. To the best of our knowledge, this is the first report on the dual-wavelength laser operation of Tm3+-single-doped solid-state laser at 1.9 and 2.3 µm. The higher optical conversion efficiency, smaller wavelength competition effect and simultaneous dual-wavelength output make this Tm-doped solid-state laser have potential application in medical surgery.

Cavity-enhanced Raman spectroscopy with optical feedback frequency-locking for gas sensing.

A cavity-enhanced Raman spectroscopy (CERS) gas-sensing method is introduced. Using optical feedback frequency-locking, laser radiation provided by a diode laser is coupled into a three-mirror V-shaped optical cavity. An intracavity laser power of 92 W is realized, yielding a power gain factor of 2200. Raman spectrums of air, carbon dioxide, and acetylene are recorded as a demonstration. Multicomponent gas mixtures including isotopic gases can be simultaneously sensed by CERS. With 200 s exposure time, detection limits of 5.35 Pa for N2, 5.07 Pa for O2, 1.74 Pa for CO2, and 0.58 Pa for C2H2 are achieved. CERS is a powerful gas-sensing method with high selectivity and sensitivity, which also has the potential for quantitative analysis of gases with high accuracy.

Polymer dye laser pumped with green semiconductor lasers

We report the results of experiments on quasi-longitudinal pumping of a polymer dye laser by two green ( λ = 513 nm) pulsed laser diodes. The lasing thresholds, efficiency, and photostability of pyrromethenes in various polymers are studied. The efficiency of dye lasers based on pyrromethene 567 and pyrromethene 580 with a three-mirror cavity with partial astigmatism compensation exceeds 20 %.

三镜直腔结构MgO∶PPLN高效连续光参量振荡器

三镜直腔结构MgO∶PPLN高效连续光参量振荡器

THERMAL EFFECTS IN THE EYE-SAFE RING OPTICAL PARAMETRIC OSCILLATOR BASED ON KTiOPO4 CRYSTALS

For an eye-safe optical parametric oscillator (OPO) built on the basis of a three-mirror ring cavity, each section of which (the space between adjacent plane mirrors) contains a x-cut KTiOPO4 (KТР) crystal having a size of 15(х) × 7(y) × 7(z) mm3, the thermal effects due to idler wave absorption in KTP crystals were investigated. These thermal effects were evaluated by means of experimental measurement of the change in the OPO performance (divergence of the output beam and pulse energy) when transferring the OPO from the mode of generation of occasional single pulses to the mo de of generation of periodically repetitive pulses. It was found when the eye-safe OPO pumped by multimode YAG: Nd laser radiation generates 8-ns pulses with a repetition rate of 10 Hz and an energy of 30–35 mJ, thermal distortions of KTP crystals placed in metal holders at their natural air-cooling, are moderate. The total effect of positive thermolenses induced in nonlinear crystals leads to an increase in the divergence of the beam of the eye-safe OPO by 10 % and to a decrease in the efficiency of the OPO by 0.76 %, by virtue of fact that the induced thermal lenses are not ideal and thereby introduce additional aberration losses into the OPO cavity. The theoretical simulation of the OPO operation in the plane-wave approximation with the use of a system of three coupled first-order abridged differential equations showed that among three KTP crystals the KTP crystal placed first in the path of pump radiation in the OPO is the largest thermal load and the action of the most intense beams.

Generation of Coupled Modes in an Unmatched Three-Mirror Laser Cavity

An extraordinary phenomenon of generation of coupled types of oscillations with a transverse field distribution corresponding to the ТЕМ pq eigenmodes with different pairs of indices p and q in the main laser cavity and in an external cavity has been experimentally detected. The excitation of coupled modes depends on the configuration and tuning of partial cavities. To solve the system of integral equations for a three-mirror cavity with mismatched spherical mirrors in the quasioptical approximation, it has been proposed to use modified boundary conditions including the coupling coefficients for eigenmodes in partial cavities.

Comparison between optical bistabilities versus power and frequency in a composite cavity-atom system.

By making use of the changes in optical properties such as absorption and dispersion around the resonance generated via electromagnetically induced transparency (EIT), we theoretically and experimentally investigate a "∞"-shape optical bistability (OB) versus frequency on the probe transmission with a Λ-shape EIT window in a rubidium atomic ensemble confined in a three-mirror optical ring cavity. Compared to the traditional OB reflected by a hysteresis loop versus power, such newly demonstrated optical bistable behavior (represented by a "∞"-shape non-overlapping region) by scanning probe and cavity detuning can experience dual bistabilities and be more sensitive to the change of experimental parameters. Further, we study the relationship between vacuum Rabi splitting and the "∞"-shape OB. Such study on frequency-induced OB could effectively improve the applications related to OB such as logic-gate devices and optical information processing.

Unveiling the relationship between optical bistability and vacuum Rabi splitting

The relationship between optical bistability (OB) and vacuum Rabi splitting is experimentally demonstrated in an atomic ensemble confined in a three-mirror optical cavity. The vacuum-induced splitting and bright states can effectively affect the bistable behaviour by manipulating multiple parameters such as atomic density and detuning. Also, we observed another kind of “∞”-shape OB by scanning the probe/cavity detuning. The study can make a contribution to better understand the OB and other dynamical behaviours in a composite atom-cavity system.

Study of an electrodynamic system consisting of a laser cavity and an external weakly reflecting element

The behaviour of the electromagnetic field in a three-mirror laser cavity is described using the method of integral equations. The results of numerical calculations and experimental studies for particular examples implementing the considered configuration are presented. The conditions for optimal tuning of a laser interferometer-deformograph with a three-mirror cavity are determined. The contribution of the reflected and scattered light and arising additional seismic noises to the resulting error of laser gravitational wave detectors is studied.

Diode-pumped dye laser

This letter reports diode pumping for dye lasers. We offer a pulsed dye laser with an astigmatism-compensated three-mirror cavity and side pumping by blue laser diodes with 200 ns pulse duration. Eight dyes were tested. Four dyes provided a slope efficiency of more than 10% and the highest slope efficiency (18%) was obtained for laser dye Coumarin 540A in benzyl alcohol.