Ring Laser Oscillator Research Articles

High-average-power 216 MHz Kerr lens mode-locked Yb:KGW ring laser oscillator for application to laser spectroscopy

We report the development of a ring Yb:KGW laser oscillator with an average power of 4.22 W, a pulse duration of 312 fs at a repetition rate of 216 MHz. The ring laser oscillator is purely Kerr lens mode-locked (KLM) taking advantage of the high nonlinear refractive index of the laser crystal in spite of being pumped by a multimode laser diode. To the best of our knowledge, this is the highest average power obtained from a KLM ring Yb:KGW laser oscillator. Monitoring the repetition rate fluctuations after initial warm-up of the laser cavity, a peak to valley of only 354.28 Hz during 30 min of free-running operation has been achieved. This could make a free-running ring cavity a suitable light source for application to laser spectroscopy. Using the ring laser oscillator, we have measured the absorption of the second overtone of the ν1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ u _1$$\\end{document} mode of NH3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document}. We have also measured absorption spectra of the Yb:KGW crystal to evaluate the quality of the crystal affected by the doped impurities.

A thin-disk ring laser oscillator at a repetition rate beyond 120 MHz

We report a Kerr lens mode-locked thin-disk ring laser oscillator with an output power of 22 W and a pulse duration of 711 fs. A repetition rate of 120.7 MHz is the highest ever obtained from a thin-disk ring laser oscillator, to the best of our knowledge. This work is expected to open up another route in dual-frequency-comb spectroscopy using a single ring laser source.

Observation of harmonic beams inside a Kerr lens mode-locked thin-disk ring laser oscillator beyond a repetition rate of 10 MHz

We report the highest intra-cavity pulse energy of 80 μJ inside a Kerr lens mode-locked thin-disk ring laser oscillator at a repetition rate beyond 10 MHz enabling observation of the 2nd and 3rd harmonic beams directly generated by the Kerr medium. By adding a tight focusing setup to the ring cavity, we could observe krypton gas flame at an intra-cavity peak intensity of ∼28 TW/cm2 yielding a conversion efficiency of 10−5 for the 3rd harmonic beam. A further upgrade of the ring oscillator could lead to realizing a table-top source of vacuum ultraviolet pulses for application in photoelectron spectroscopy.

Handheld nonlinear microscope system comprising a 2 MHz repetition rate, mode-locked Yb-fiber laser for in vivo biomedical imaging.

A novel, Yb-fiber laser based, handheld 2PEF/SHG microscope imaging system is introduced. It is suitable for in vivo imaging of murine skin at an average power level as low as 5 mW at 200 kHz sampling rate. Amplified and compressed laser pulses having a spectral bandwidth of 8 to 12 nm at around 1030 nm excite the biological samples at a ~1.89 MHz repetition rate, which explains how the high quality two-photon excitation fluorescence (2PEF) and second harmonic generation (SHG) images are obtained at the average power level of a laser pointer. The scanning, imaging and detection head, which comprises a conventional microscope objective for beam focusing, has a physical length of ~180 mm owing to the custom designed imaging telescope system between the laser scanner mirrors and the entrance aperture of the microscope objective. Operation of the all-fiber, all-normal dispersion Yb-fiber ring laser oscillator is electronically controlled by a two-channel polarization controller for Q-switching free mode-locked operation. The whole nonlinear microscope imaging system has the main advantages of the low price of the fs laser applied, fiber optics flexibility, a relatively small, light-weight scanning and detection head, and a very low risk of thermal or photochemical damage of the skin samples.

Suppression of thermal frequency noise in erbium-doped fiber random lasers

Frequency and intensity noise are characterized for erbium-doped fiber (EDF) random lasers based on Rayleigh distributed feedback mechanism. We propose a theoretical model for the frequency noise of such random lasers using the property of random phase modulations from multiple scattering points in ultralong fibers. We find that the Rayleigh feedback suppresses the noise at higher frequencies by introducing a Lorentzian envelope over the thermal frequency noise of a long fiber cavity. The theoretical model and measured frequency noise agree quantitatively with two fitting parameters. The random laser exhibits a noise level of 6 Hz²/Hz at 2 kHz, which is lower than what is found in conventional narrow-linewidth EDF fiber lasers and nonplanar ring laser oscillators (NPROs) by a factor of 166 and 2, respectively. The frequency noise has a minimum value for an optimum length of the Rayleigh scattering fiber.

Effects of Gaussian fields on the stability of inhomogeneously broadened lasers

Under some conditions, spontaneous coherent pulsations are known to occur in the output beams of inhomogeneously broadened laser oscillators. These lasers typically operate with a Gaussian transverse field distribution, while the corresponding theoretical models assume a uniform-plane-wave field. The effects of a Gaussian field on the stability criteria of single-mode inhomogeneously broadened ring laser oscillators are considered in this study. It is found that in comparison to a plane wave a Gaussian field variation still permits low-threshold spontaneous pulsations but reduces the parameter space over which these pulsations can be observed.

Frequency stabilization of a Q-switched Nd:YAG laser oscillator with stability better 300 kHz following an rf-sideband scheme

A frequency stabilization scheme following the Pound-Drever-Hall technique modified with a sample and hold circuit has been applied to a Q-switched diode-pumped Nd:YAG ring oscillator. The high-power ring is injection seeded by a monolithic non-planar ring laser oscillator (NPRO). The slave oscillator emits pulses of 23 ns duration and 20 mJ pulse energy with almost diffraction limited beam quality ( M 2 = 1.2) at a repetition rate of 400 Hz. The short-term fluctuation of the center frequency from pulse to pulse is 290 kHz. The oscillator is designed for applications within lidar measurements.

55-fs pulse generation without wave-breaking from an all-fiber Erbium-doped ring laser

We demonstrate the direct generation of 55 fs pulses from an all-fiber Erbium-doped ring laser oscillator using the nonlinear polarization rotation mode-locking. The average output power is 56.4 mW but limited by available pump power of 330 mW. The linear chirped pulse duration is 55 fs after recompression using standard single-mode fiber. The pulses show to resist optical wave breaking with a smooth spectrum without any side lobe and cw-breakthrough. This all-fiber laser exhibits relatively high transfer efficiency of 17% and the single pulse energy reaches 1.5 nJ.

Effects of focusing-beam field variations on the stability of laser oscillators

Semiclassical models for the dynamical behavior of single-longitudinal-mode, homogeneously broadened, unidirectional ring-laser oscillators have long been available. However, in most of these models the beam's cross section is assumed to be independent of longitudinal position in the laser, while in practical laser systems it is common for the diameter to vary with position. A model for lasers with focusing-beam field variations is developed here. Linear stability analysis shows that higher values of excitation are required to reach the type 1 instability threshold for lasers with longitudinal variations of the beam diameter than for the uniform plane-wave laser model.

Simple 1 micron ring laser oscillators pumped by fiber-coupled laser diodes

We have designed simple nonplanar Nd:YAG ring laser oscillators that utilize all flat mirrors and are pumped by the fiber-coupled output from ten 3 watt diode lasers. We have obtained up to 8.5 W at 1.06 microns of diffraction-limited, single frequency output with no measureable astigmatism or ellipticity with a total pump power of 26 W from a pair of 400 micron diameter fibers. Convex curved surfaces on the Nd:YAG rod are used to increase the cavity mode size at the rod while minimizing the contribution of aspheric thermal lensing. Comparison to a linear cavity with no intracavity polarizing element indicates that stress depolarization is a significant loss mechanism in the ring laser. The cavity design is also suitable for use with birefringent laser media, such as Nd:YLF or Nd:YVO/sub 4/. >

Spontaneous coherent pulsations in standing-wave laser oscillators: stability criteria for homogeneous broadening

The stability criteria for single-mode standing-wave laser oscillators in the homogeneously broadened limit are reported, and two types of criteria are distinguished. The first type (type 1) corresponds to the minimum value of the threshold parameter for which an infinitesimal perturbation away from steady state grows into an oscillatory solution. A second type (type 2) corresponds to the minimum value of threshold parameter for which large-amplitude oscillations do not decay to the steady-state solution. Undamped pulsations in single-mode homogeneously broadened standing-wave laser oscillators are found to occur at a much higher excitation level than in ring-laser oscillators with homogeneous broadening. The effects of detuning on the stability criteria are also investigated.

Fast frequency tuning and phase locking of diode-pumped Nd:YAG ring lasers

We have built a diode-pumped single-mode monolithic Nd:YAG ring-laser oscillator that can be tuned piezoelectrically over several tens of megahertz in a few microseconds. Frequency stability over 1 msec is better than 500 Hz. We have electronically phase locked two lasers for periods of minutes with phase noise of 29 mrad rms.

Spontaneous coherent pulsations in ring-laser oscillators: stability criteria

The stability criteria implied by a simplified semiclassical laser model are considered in detail. It is found that two types of criteria must be distinguished. The first concerns the smallest pump rate for which infinitesimal perturbations of the steady-state solution will increase with time, and the second concerns the smallest pump rate for which large amplitude modulations will not damp away.

Spontaneous coherent pulsations in ring-laser oscillators: simplified models

A series of simplifications is introduced in the general model for spontaneous pulsations in ring-laser oscillators. These simplifications can lead to more-efficient numerical computations and a better understanding of specific ingredients in the model. Among the approximations investigated are neglect of spectral cross relaxation, neglect of multiple-energy-level equations, neglect of electric-field derivatives, and neglect of polarization derivatives. Although some of these approximations have little effect, others eliminate the spontaneous pulsations.

Ultrashort pulse generation by Nd^3+:glass and Nd^3+:YAG lasers

By injecting single subnanosecond pulses into a latent ring-laser oscillator, it is possible to generate highly reproducible intense trains of short pulses from a solid-state laser. In this way, 12-psec pulses are available from a high-repetition-rate Nd3+:YAG laser, whereas Nd3+:phosphate glass reliably produces pulses of <3-psec duration. Further compression of the Nd3+:YAG laser pulses can be accomplished by the insertion of a passive phase modulator into the cavity, yielding pulses of ≥5-psec duration and >3-cm−1 bandwidth.

Lasing regimes and emission characteristics of a ring iodine photodissociation laser

An experimental investigation was made of the energy, space-time, and polarization characteristics of an atomic iodine photodissociation laser with a four-mirror ring resonator. The direction of lasing was governed mainly by weak reverse signals which could originate, in the absence of auxiliary mirrors, from parasitic reflections or scattering. Under flashlamp pumping, an influence of dynamic inhomogeneity waves on the lasing threshold was manifested in the space-time structure of the near-field pattern. It was established that the polarization of the emitted radiation was linear in the absence of external magnetic fields. It was shown that one can use a ring-laser oscillator for investigations on amplifying systems, and that this approach ensures suppression of amplifier self-excitation by reflection from the resonator mirrors.