Four-mirror Cavity Research Articles

High-efficiency blue light generation at 426 nm in low pump regime

We report high-efficiency Ti:sapphire-laser-based frequency doubling at the cesium D2 line 852 nm using a 20 mm-long periodically-poled potassium titanyl phosphate crystal in a bow-tie four-mirror ring enhancement cavity. The relatively complete cavity design procedure is presented. Focusing that is over twice as loose as optimal focusing is used, and both the fundamental frequency wave and second harmonic beam absorption-induced thermal lensing effects are weakened. Blue light of 210 mW at 426 nm, where absorption is severe, was obtained with 310 mW mode-matched fundamental light, corresponding to conversion efficiency of up to 67%. The blue light beam power showed 1.5% RMS fluctuation over 40 min.

Comparison and characterization of efficient frequency doubling at 397.5 nm with PPKTP, LBO and BiBO crystals

A continuous-wave Ti:sapphire laser at 795 nm is frequency doubled in a bow-tie type enhancement four-mirror ring cavity with LiB3O5 (LBO), BiB3O6 (BiBO), and periodically polled KTiOPO4 (PPKTP) crystals, respectively. The properties of 397.5 nm ultra-violet (UV) output power, beam quality, stability for these different nonlinear crystals are investigated and compared. For PPKTP crystal, the highest doubling efficiency of 58.1% is achieved from 191 mW of 795 nm mode-matched fundamental power to 111 mW of 397.5 nm UV output. For LBO crystal, with 1.34 W of mode-matched 795 nm power, 770 mW of 397.5 nm UV output is achieved, implying a doubling efficiency of 57.4%. For BiBO crystal, with 323 mW of mode-matched 795 nm power, 116 mW of 397.5 nm UV output is achieved, leading to a doubling efficiency of 35.9%. The generated UV radiation has potential applications in the fields of quantum physics.

Cavity-enhanced frequency doubling from 795nm to 397.5nm ultra-violet coherent radiation with PPKTP crystals in the low pump power regime.

We demonstrate a simple, compact and cost-efficient diode laser pumped frequency doubling system at 795 nm in the low power regime. In two configurations, a bow-tie four-mirror ring enhancement cavity with a PPKTP crystal inside and a semi-monolithic PPKTP enhancement cavity, we obtain 397.5nm ultra-violet coherent radiation of 35mW and 47mW respectively with a mode-matched fundamental power of about 110mW, corresponding to a conversion efficiency of 32% and 41%. The low loss semi-monolithic cavity leads to the better results. The constructed ultra-violet coherent radiation has good power stability and beam quality, and the system has huge potential in quantum optics and cold atom physics.

X-ray generation by inverse Compton scattering at the superconducting RF test facility

Quasi-monochromatic X-rays with high brightness have a broad range of applications in fields such as life sciences, bio-, medical applications, and microlithography. One method for generating such X-rays is via inverse Compton scattering (ICS). X-ray generation experiments using ICS were carried out at the superconducting RF test facility (STF) accelerator at KEK. A new beam line, newly developed four-mirror optical cavity system, and new X-ray detector system were prepared for experiments downstream section of the STF electron accelerator. Amplified pulsed photons were accumulated into a four-mirror optical cavity and collided with an incoming 40MeV electron beam. The generated X-rays were detected using a microchannel plate (MCP) detector for X-ray yield measurements and a new silicon-on-insulator (SOI) detector system for energy measurements. The detected X-ray yield by the MCP detector was 1756.8±272.2 photons/(244 electron bunches). To extrapolate this result to 1ms train length under 5Hz operations, 4.60×105 photons/1%-bandwidth were obtained. The peak X-ray energy, which was confirmed by the SOI detector, was 29keV, and this is consistent with ICS X-rays.

Polarization-selectable cavity locking method for generation of laser Compton scattered γ-rays

Nowadays, generation of energy-tunable, monochromatic γ-rays is needed to establish a nondestructive assay method of nuclear fuel materials. The γ-rays are generated by collision of laser photons stored in a cavity and relativistic electrons. We propose a configuration of an enhancement cavity capable of performing polarization control fabricated by a combination of a four-mirror ring cavity with a small spot inside a cavity and a three-mirror of reflective optics as an image inverter for polarization-selectable γ-rays. The image inverter introduces a phase shift of specific polarization which can be used to generate an error signal to lock an optical cavity at a resonance condition.

Self-mixing interference effect based on fiber laser

For the sensing applications based on the self-mixing interference technology of fiber laser, the self-mixing interference in the linear cavity fiber laser is theoretically analyzed through a four-mirror cavity model. The output power and frequency equation are deduced, and the behaviors of the laser under different optical feedback strengths are analyzed and simulated as well. The intensity of the laser is modulated by the length of the external cavity, and one fringe of the signal corresponds to the displacement of half wavelength of the target. Experimental setup is developed to validate the theoretical analysis. The obtained results provide both the theoretical and experimental basis for further studying self-mixing interferemetric sensing applications of fiber lasers.

2.1 μm four-mirror standing-wave optical parametric oscillator with high brightness and efficiency

We report a high-brightness and high-efficiency degenerate periodically poled MgO:LiNbO3 (PPMgLN) optical parametric oscillator (OPO), configured with a four-mirror standing-wave cavity and pumped by a Q-switched Nd:YVO4 laser. Attributed to the successful mode matching of four-mirror standing-wave cavity, we have obtained good beam qualities both in single-pass and double-pass geometry. The beam qualities of single-pass pump geometry are M2 ∼ 1.6 and 1.7 in the horizontal and vertical directions, and the beam qualities of double-pass pump geometry are M2 ∼ 1.8 and 1.9. Optical to optical conversion efficiencies of 38% and 55% are achieved, respectively. With a volume Bragg grating used as the output coupler, we achieved a narrow linewidth of less than 2 nm.

Passive Q-switched mode locking of a diode-pumped Tm:SSO laser near 2 μm

With a fiber-coupled 790 nm laser diode array as the pump source and a 4 at.% Tm:Sc2SiO5 (Tm:SSO) crystal, laser action near 2 μm wavelength was successfully obtained with a compact four-mirror fold cavity. Using broadband carbon nanotube as the saturable absorber, a passively Q-switched mode-locked (QML) Tm:SSO laser is realized for the first time. 100% modulation depth of mode locking has been achieved. The duration of the mode-locked pulse is estimated to be about sub-100 ps with 92.6 MHz repetition rate within a Q-switched pulse envelope. The spectrum of the QML laser is centered at 1967.4 nm with a broad spectral region of ∼23 nm. A maximum average output power of 195 mW and Q-switched pulse energy of 4.7 μJ is obtained. The dependence of the operational parameters on pump power was also investigated experimentally.

Nd:GdVO4 ring laser pumped by laser diodes

The design and operation of a laser diode-pumped Nd:GdVO4 ring laser is described. A composite crystal (Nd:GdVO4/YVO4) with undoped ends is single-end pumped by a fiber-coupled laser diode (LD) at 808 nm. A four-mirror ring cavity is designed to keep the laser operating unidirectionally, which eliminates spatial hole burning in the standing-wave cavity. This laser can operate either as continuous wave (CW) or Q-switched. The single-frequency power obtained was 9.1 W at 1063 nm. Q-switched operation produced 0.23 mJ/pulse at 20 kHz in the fundamental laser.

Design studies on compact four mirror laser resonator with mode-locked pulsed laser for 5 μm laser wire

A compact prototype four-mirror optical cavity is being constructed at KEK-ATF to measure low-emittance electron beams in the damping ring. Four-mirror-resonators reduce the sensitivity to the misalignment of mirrors in comparison to two mirror-resonators. The aspect ratio is important when constructing a compact resonator with a very small beam waist of less than 5μm. The total cavity length of a four-mirror resonator is matched according to the pulse repetition of mode-locked laser oscillator. Minimum beam waist is obtained in the sagittal plane using an IR pulsed laser. The advantage of such types of compact four-mirror-resonators is the total scanning time for measurement of the beam profile is much shorter in comparison to a CW laser wire system. By using a pulsed green laser that has been converted to the second harmonics from an IR pulsed laser, a minimum beam waist that has half the beam waist when using an IR laser oscillator can be obtained. Therefore, it is possible to obtain the beam waist of less than 5μm (σ value) that is required for effective photon–electron collision. We report on the development and performance studies for such types of compact four-mirror laser wire systems.

186 W cw single-frequency 1319 nm ring laser pumped at 885 nm

A 1.86 W cw single-frequency 1319 nm laser was produced by using an 885 nm-pumped Nd:YAG crystal with a compact four-mirror ring cavity, for the first time to our knowledge. The Nd:YAG produced a slope efficiency of 21% and an optical-to-optical efficiency of 18% with respect to the absorbed diode pump power. A near-diffraction-limited beam with M(2)=1.2 was achieved under the maximum output power.

Non-planar four-mirror optical cavity for high intensity gamma ray flux production by pulsed laser beam Compton scattering off GeV-electrons

As part of the R&D toward the production of high flux of polarised Gamma-rays we have designed and built a non-planar four-mirror optical cavity with a high finesse and operated it at a particle accelerator. We report on the main challenges of such cavity, such as the design of a suitable laser based on fiber technology, the mechanical difficulties of having a high tunability and a high mechanical stability in an accelerator environment and the active stabilization of such cavity by implementing a double feedback loop in a FPGA.

Production of gamma rays by pulsed laser beam Compton scattering off GeV-electrons using a non-planar four-mirror optical cavity

As part of the positron source R&D for future e+−e− colliders and Compton based compact light sources, a high finesse non-planar four-mirror Fabry-Perot cavity has recently been installed at the ATF (KEK, Tsukuba, Japan) [1]. The first measurements of the gamma ray flux produced with a such cavity using a pulsed laser is presented here. We demonstrate the production of a flux of 2.7 ± 0.2 gamma rays per bunch crossing ( ∼ 3 × 106 gammas per second) during the commissioning.

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.

7.5 W Nd:GdVO4环形腔单频激光器

A Nd:GdVO4 crystal is end-pumped by a fiber-coupled laser diode(FCLD), and high power of single-frequency laser output is achieved. The four-mirror bow-tie ring cavity with a Faraday rotator and a half wave plate is applied to eliminate the spatial hole-burning effect. A solid etalon is inserted into the cavity to obtain single-frequency1063 nm output of the narrow line width. The maximum output is7.57 W and the optical-optical conversion efficiency is41.8% with18.10 W of the incident power.

Performances of ‘G-Pisa’: a middle size gyrolaser

G-Pisa is an experiment dealing with a high sensitivity laser gyroscope with an area of the order of . It aims at improving the performances of mirror suspensions of the future-generation gravitational-wave antenna Virgo. The experimental set-up consists in a He–Ne ring laser with a four-mirror square cavity. The device is operational on a stable regime, with the laser operating in both single mode or multi mode. The low-frequency sensitivity, 0.001–, is limited by the environmental noise, but it has been checked that the requirements for the inverted pendulum tilt control given for AdVirgo are fulfilled ( at 30 MHz).

High finesse Fabry–Perot cavities in picosecond regime

An R&D activity on high finesse passive Fabry–Perot cavities locked to a mode-locked oscillator is described. A new nonplanar four-mirror cavity geometry is proposed to provide stable laser cavity locking operations. Future developments of this R&D are also given.

Intracavity power addition with a close-ended composite four-mirror cavity

We present a novel four-mirror cavity with two active gains to combine power intracavity and also give a detailed theoretical analysis of the combined gain. By using the effective field method, the four-mirror cavity with two gain media can be regarded as a linear resonator with one effective combined gain (ECG), and we procure a theoretical model of the ECG and deduce its exact analytical expression. When the two branch gains are close to each other, the combined gain can be reduced to their product, and the simplified presentation of ECG has been demonstrated. The combined output power which directly reflects the small signal ECG of the four-mirror cavity is studied experimentally, and the results are in good agreement with the theoretical ones.

Amplitude—phase mode structure of an astigmatic Gaussian beam in ring lasers with a nonplanar four-mirror cavity and an aperture

The structure of the fundamental mode field in a nonplanar ring four-mirror resonator with an aperture is determined taking into account rotations of the amplitude and phase distributions of an astigmatic Gaussian beam. The rotation angles of the axes of these distributions are calculated upon variations in the characteristic aperture size and the angle of curvature (nonplanarity) of the resonator. The effect of the resonator aperture and nonplanarity on the intensity distribution of the interference pattern behind a mixer is studied. It is shown that interference fringes have a slope depending on the orientations of the amplitude and phase distributions of the mode.

Generation of 2.1 W Continuous Wave Blue Light by IntracavityDoubling of a Diode-End-Pumped Nd:YAG Laser in a 30 mm LBO

A folded four-mirror cavity with a composite Nd:YAG rod is optimized toobtain high efficient cw 473 nm blue output. The laser could operatestably in the region of the thermal-lens focal length from 20 mm to70 mm. LBO is used for intracavity frequency doubling of the 946 nmtransition of Nd:YAG and the optimum LBO length is investigated. Amaximum output power of 2.1 W in the blue spectral range at 473 nm isachieved with 30-mm-long LBO, corresponding to an optical conversionefficiency of 9.1%.