Five-beam magneto-optical trap and optical molasses

We have operated a magneto-optical trap and optical molasses for the laser cooling of cesium atoms on the basis of a five-beam laser configuration. For the magneto-optical trap two laser beams counterpropagate along the axis of a quadrupole trap and the remaining three beams propagate in the orthogonal plane at 120° to each other. The same optical configuration was used for the optical molasses. We have tested the efficiency in atom collection and the temperatures reached in both cooling processes. In comparison to previous results on a six-beam configuration, a lower number of atoms is collected, while comparable densities are realized. The atomic temperatures have been measured through a delayed shadow-image technique, where one of the running-wave cooling beams produces an absorptive image of the atoms on a camera. Received: 14 January 1999 / revised version: 23 June 1999 / Published online: 8 September 1999     

29.2 W, 20 kHz linewidth all fiber single-frequency MOPA laser

We demonstrate a high power all fiber single-frequency MOPA laser. The center wavelength of the single-frequency fiber laser seed is 1064 nm with a linewidth narrower than 20 kHz. A two-stage power amplification configuration is employed. A single-frequency fiber laser with an output power of 29.2 W is obtained, and the optical to optical efficiency is 78%.     

Driving and analysis of micro-objects by digital holographic microscope in microfluidics

We propose an optical configuration in which floating particles in a microfluidic chamber can be characterized by an interference microscopy configuration to obtain quantitative phase-contrast maps. The configuration is simply made by two laser beams from the same laser source. One beam provides the optical forces for driving the particle along appropriate paths, but at same time works as the object illumination beam in the holographic microscope. The second beam plays the role of the reference beam, allowing recording of an interference fringe pattern (i.e., the digital hologram) in an out-of-focus image plane. The system and method are illustrated and experimental results are offered for polymeric particles as well as for in vitro cells with the aim to demonstrate the approach.     

Self-pulsing in Er3+-doped fibre laser

The output intensity of an erbium-doped fibre laser was studied. Experiments were performed with three pumping wavelengths: 514.5 nm, 810 nm and 980 nm. The laser output intensity exhibits three different dynamical behaviours: steady-state, sinusoidal variation or self-pulsing. In particular, in a bad (high-loss) cavity configuration, when the pumping ratio is increased above the lasing threshold the output intensity changes continuously from a steady-state to an infinite train of pulses. We also show that, depending on the cavity configuration, the transient oscillations display different forms.     

Directivity influence of signals propagation through EDFA gain medium of Brillouin-erbium fiber laser

We experimentally demonstrate a multiwavelength Brillouin-erbium fiber laser in two configurations; uni-directional and bi-directional propagation of Brillouin pump and Brillouin Stokes signals through an Erbium-doped fiber gain. The influence of these configurations on the performance of the output parameters in terms of lasing threshold, output channel generation and tuning range of the generated output channels are investigated. We discovered that there is a trade-off between these two fiber laser configurations. The uni-directional amplifier configuration provides greater tuning range of 46.8 nm against 23 nm at maximum Brillouin pump power of 2 mW and 1480-nm pump power of 130 mW. On the other hand, the bi-directional amplifier configuration provides 13 output channels against 6 output channels obtained from the uni-directional amplifier configuration at the same pumping powers. Nevertheless, the bi-directional amplifier configuration requires much lower pump power to initiate lasing.     

Simple and compact 1-Hz laser system via an improved mounting configuration of a reference cavity

We report an improved mounting configuration for a passive optical cavity used for laser frequency stabilization. The associated reduction of the vibration sensitivity of the effective cavity length has led to a simple and compact reference cavity system for laser stabilization at the level of 1 Hz linewidth.     

Refractive-index saturation-mediated multiple line emission in polymer thin-film distributed-feedback lasers

We report experimental and theoretical investigations of multiple laser-line emission in a distributed-feedback dye laser pumped by two coherent optical beams. We have used a Lloyd interferometer configuration with second- and third-order Bragg reflections to study the interaction between the two incident pumps in an organic thin film. We demonstrated theoretically that the number of laser emission lines can be interpreted with reference to the saturation effect in the refractive index.     

All-fiber mode-locked fiber laser

An environmentally stable mode-locked fiber laser based on nonlinear polarization rotation is experimentally demonstrated. The laser is based on a novel laser configuration that has negligible low-power steady-state reflectivity from one side and, consequently, no CW gain. The laser is self starting and the configuration is implementable as an all-fiber laser with standard polarization-maintaining fiber-pigtailed components. A pulse duration of 5.6 ps is obtained at a repetition rate of 5.96 MHz and at an average power of 8 mW. As an application of the proposed laser configuration, 213 mW of supercontinuum (600-1750 nm) was demonstrated from a fiber laser system with no sections of free-space optics.     

Efficient high-power self-frequency-doubling Nd:GdCOB laser at 545 and 530 nm

We report an efficient high-power self-frequency-doubling (SFD) Nd:GdCOB laser. The maximum output power is 3.01 W at a wavelength of 545 nm with an optical efficiency of 20.7%, which, to our knowledge, is the highest SFD laser output power and efficiency yet obtained. By optimizing the configuration and cut orientation of the Nd:GdCOB crystals, a SFD laser at a wavelength of about 530 nm was achieved with a maximum output power of 1.32 W. We propose that these SFD lasers will have promise in applications such as laser displays, medical treatment, spectroscopic analysis, etc.     

Picosecond Nd:YLF five-passes laser amplifier with 20 mJ pulse energy

We have demonstrated an all-diode-pumped Nd:YLF laser amplifier that produces 20.8 mJ pulses of 12.9 ps duration at 10 Hz repetition rate. The laser system consists of a mode-locking oscillator, a regenerative amplifier and a five-pass amplifier. The small-angle off-axis five-pass configuration combining with the gradual expansion of the laser beam cross section makes the amplifier compact and effective.     

Emission Dependence on Length in a 1.48-mum Pumped Erbium-Doped Laser with an All-Fiber Configuration

We report a study on the main features of a 1.48-mum pumped erbium-doped fiber laser, such as threshold pump power, output power, and slope efficiency. In particular we have focused on its dependence on active fiber length. We employed an all-fiber laser configuration, which included mirrors directly coated onto the polished fiber endfaces. Launched pump power and laser output power were introduced and extracted, respectively, from the laser cavity by means of couplers. Our measure ments show the existence of an optimum erbium-doped fiber length, where threshold power reaches minimum and output power maximum.     

73-nm tuning of a double-clad Yb<Superscript>3+</Superscript>-doped fiber laser based on a hybrid array

We report on a wide wavelength tuning in a double-clad ytterbium-doped fiber laser. The laser cavity consists of an array of broadband high-reflection fiber Bragg gratings and a bulk grating as the output coupler and wavelength selection element. The proposed fiber laser configuration combines a low intracavity loss of the fiber Bragg grating mirrors with a wide wavelength tuning of the bulk gratings. We demonstrate a >70-nm wavelength tuning range, limited only by the available fiber Bragg gratings.     

Creation of Molecular Vortex

The molecular vortex is predicted to be generated from an atomic Bose-Einstein condensate through the two-color photoassociation process with a specially designed field configuration in which a Gaussian and a first-order Laguerre Gaussian laser beam are applied between the bound-bound and free-bound transition, respectively. We show that such a configuration can lead to a coherent superposition of an atomic condensate and a molecular quantized vortex. We develop stimulated adiabatic passages to minimize the effect of mean-field shifts due to collisions for optimal conversi9n of an atomic condensate into a ground molecular vortex.     

22 W single mode tm-doped fiber MOPA in all-fiber format

We demonstrate an all-fiberized laser in main oscillator power amplification (MOPA) configuration with 22 W output power and a central wavelength of 1950 nm. The laser is pumped by pigtailed laser diode with a central wavelength of 793 nm. Strictly single-mode can be obtained and the optical to optical efficiency of the fiber laser is 40% with respect to the pump power. No power-roll is observed and the power can be scaled straightforwardly by using more pump sources.     

Effect of the External Mirror Feedback Strength in the Dynamics and Spectrum of the Injected Semiconductor Lasers

We analytically investigate the effect of an external mirror on the stability of an injected semiconductor laser, the latter treated as injected damped oscillators. In the studied configuration, the injected semiconductor laser with an external mirror is under the influence of a chaotic oscillating optical signal that is generated by a similar semiconductor master laser. We derive our results in terms of the damping rate and resonance frequency. We show that the external mirror can eliminate the unstable modes of the injected laser at low frequencies. Furthermore, the mirror can enhance the damping of the oscillation modes of the injected semiconductor laser; consequently, the driven response of the injected laser may have a broad spectrum, even wider than that of the chaotic driving signal. We also show results for the bandwidths of the injection amplitude and phase increment as functions of the injection rate and feedback strength of the external mirror. In addition, we use bifurcation and time-series curves to describe the dynamical behavior of the injected laser. We identify the feedback strength of injected laser, relative to that of the master laser, which induces synchronization between the injected-laser oscillation modes and the master laser.     

Operation of a high power,broadly tunable infrared dye laser

We discuss the operation and performance of a ruby pumped infrared dye laser with a wide tuning range and a high out-put power. The longitudinally pumped infrared laser was operated in the Littrow configuration without an intracavity beam expander. The dye, IR 125, exhibited a tunability range that extended from 8325 Å to 9375 Å. The dye laser had a pulse duration of 20 ns and an output power of 12.5 MW with a 2.3 joule ruby pump. The maximum output power of the infrared laser was limited by the damage threshold of the tuning element.     

Diode-side-pumped intracavity frequency-doubled Nd:YAG/BaWO4 Raman laser generating average output power of 3.14 W at 590 nm

We report a linear-cavity high-power all-solid-state Q-switched yellow laser. The laser source comprises a diode-side-pumped Nd:YAG module that produces 1064 nm fundamental radiation, an intracavity BaWO(4) Raman crystal that generates a first-Stokes laser at 1180 nm, and a KTP crystal that frequency doubles the first-Stokes laser to 590 nm. A convex-plane cavity is employed in this configuration to counteract some of the thermal effect caused by high pump power. An average output power of 3.14 W at 590 nm is obtained at a pulse repetition frequency of 10 kHz.     

Fabrication and characterization of a pulsed fiber ring laser based on As2S3

We demonstrate the operation of a fiber ring laser using a 19.5 cm segment of As2S3 chalcogenide fiber. The laser is passively mode-locked via nonlinear polarization rotation and provides two different operation regimes of picosecond and noiselike pulses. This ring configuration also enables an accurate measurement of the chromatic dispersion of the chalcogenide fiber.     

Diffractive scanning mechanism for laser marker

We present a new idea of marking based on spectral properties of CO₂ laser radiation. The idea has been illustrated on RF excited waveguide CO₂ lasers in different configurations: single channel, multi-waveguide and slab-waveguide ones. The pulse operation of the laser has been considered as well. The advantage of the presented diffraction marker is avoiding complicated and fallible mechanical elements. The only executive elements of the marker are a diffraction grating and a piezoceramic transducer. It has been shown that the slab-waveguide configuration of the RF excited CO₂ laser equipped with an unstable resonator is the most promising configuration for application to the diffraction marker.     

Short pulse eye-safe laser with a stimulated Raman scattering self-conversion based on a Nd:KGW crystal

We present the results of a solid self-Raman laser based on a Nd:KGW crystal that is transversely pumped by laser diode bars. A beam of an eye-safe laser with a 31.8 mJ output energy and a 2.0 ns pulse width was obtained by applying a special s-polarized reflective resonator configuration in which the length of the Raman resonator was shorter than that of the fundamental radiation resonator. The eye-safe laser has the highest output energy and the shortest pulse width among the Nd:KGW lasers ever reported.