CW Oscillation Research Articles

GaInAsP/InP SBH surface emitting laser with Si/Al 2 O 3 mirror

An Si/Al/sub 2/O/sub 3/ mirror has been introduced into the p-side mirror of a 1.3 /spl mu/m GaInAsP/InP square buried heterostructure (SBH) surface emitting (SE) laser to decrease thermal resistance. The low threshold pulsed oscillation (threshold current I/sub th/=12 mA) has been obtained for an 8/spl times/8 /spl mu/m device at room temperature. Its threshold current density was /spl sim/18 kA/cm/sup 2/. Near room temperature (13/spl deg/C) CW oscillation for another chip has also been realised. >

New CO/sub 2/ laser lines in the 11-μm wavelength region: new hot bands

Nineteen new laser lines in the 11-/spl mu/m wavelength region have been observed in CW oscillation from a CO/sub 2/ laser with a high-Q, high-resolution cavity at a higher than usual current density. The frequency of each line has been measured using heterodyne frequency measurement techniques. Analysis of the frequencies shows that 15 lines are rotation-vibration transitions of the 01/sup 1/2-[11/sup 1/1,03/sup 1/1]/sub I/ band (the first sequence hot band) of the CO/sub 2/ molecule and four lines belong to the rotation-vibration transitions of the 02/sup 2/1-[12/sup 2/0, 04/sup 2/0]/sub I/ band of CO/sub 2/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Bistability in self-mode-locked lasers with radially varying gain

Theoretically discussed is the emergence of bistability in self-mode-locking without apertures by using a Gaussian beam approximation in which both spatial and temporal effects are simultaneously taken into account. It is shown that cavity configuration where mode-locking operation is favoured lead to a bistable behavior in the pulse characteristics and the transition from the lower-to the upper-branch favours the suppression of cw oscillations.

GaInAsP lateral current injection lasers on semi-insulating substrates

GaInAsP lateral current injection lasers have been fabricated on semi-insulating InP substrates. The lasers exhibit good lasing characteristics such as 10 mA threshold current, 10 mW maximum cw output power, and cw oscillation up to 70/spl deg/C. The laser has very low capacitance of 0.5 pF at zero bias voltage. This performance shows, for the first time, that the lateral current injection laser is a promising candidate for OEIC light sources. >

Neodymium-doped silica-based planar waveguide lasers

Fabrication and lasing characteristics of Nd-doped P/sub 2/O/sub 5/-SiO/sub 2/ core planar waveguide lasers are described. CW oscillation at a wavelength of 1052.5 nm was successfully demonstrated in 0.2 wt%-Nd-doped silica-based planar waveguides fabricated on a silicon substrate by flame hydrolysis deposition and reactive ion etching. The lasing threshold and slope efficiency were optimized in an 8-/spl mu/m-wide waveguide, in which a lasing threshold pump power of 26 mW and a slope efficiency of 2.0% were obtained for 805-nm pumping. The measured lasing characteristics agreed with theoretical characteristics calculated by employing finite-element waveguide analysis, indicating that the waveguide structure was well controlled by the developed waveguide fabrication technique. The possible lasing characteristics of the waveguide lasers are discussed based on this agreement. The attenuation and emission properties of the waveguides are also described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Self-starting sliding-frequency fibre soliton laser

The authors demonstrate self-starting soliton generation by inserting a travelling wave acousto-optic modulator and a bandpass filter in a diode-pumped erbium doped fibre ring laser. The continuous frequency sliding of the circulating light inhibits CW oscillation, and favours the emission of solitons that are stably trapped by the filter.

Tensile-strained AlGaInP single-quantum-well LDs emitting at 615 nm

CW oscillation at a wavelength shorter than 630 nm, which depends on the Al content incorporated into a tensile-strained single-quantum-well active region of AlGaInP LDs, is investigated. A threshold current of 112 mA at 20°C is attained in a quaternary (AlxGa1−x)InP (x = 0.1) SQW LD emitting at 615 nm.

Self-mode locking of solid-state lasers without apertures

Numerical simulations that take into account propagation, self-focusing, and gain saturation in solid-state lasers reveal that self-mode locking can take place in such lasers even in the absence of apertures. The combination of self-focusing and gain saturation produces a differential gain that favors the growth of short pulses and eliminates cw oscillations. Nonsymmetrical cavities can provide a substantial differential gain when they are operated near a stability limit.

Time-gated gain cell for frequency-stable, single-longitudinal-mode operation of a transverse, electric, atmospheric CO2 laser

A time-gated gain cell has been demonstrated as a method for producing single-longitudinal-mode output from a pulsed transverse, electric, atmospheric (TEA) carbon dioxide laser. The gain cell is operated as an oscillator during the time between the laser pulses and is rapidly dropped below threshold during the TEA pulse output to avoid degradation of the gain-switched spike in the laser pulse. Standard dither-stabilization techniques can be used during the time between the laser pulses (cw oscillation) to position the output coupler for single-mode operation and frequency stabilization while the gain cell is operated above threshold.

High-contrast terawatt chirped-pulse-amplification laser that uses a 1-ps Nd:glass oscillator

We have developed a fiberless 1-TW all-Nd:glass chirped-pulse-amplification laser system that uses high-contrast 0.8-1.4-ps pulses produced directly from a Nd:glass feedback-controlled oscillator. Employing grating-only expansion and compression, the system produces clean (~10(7) contrast ratio) 1-J, 1- 1.4-ps recompressed pulses without added pulse cleaning. Clean microjoule-energy pulses from the oscillator require less subsequent amplification than cw oscillator schemes, thereby minimizing gain-bandwidth narrowing and offering improved contrast with amplified stimulated emission background.

Electron-beam vapour-deposited erbium-doped glass waveguide laser at 1.53 μm

A single-transverse-mode erbium-doped glass waveguide laser operating at a wavelength of 1.53 μm is described. The erbium-doped GeO2-SiO2 core of the waveguide was made by electron-beam vapour deposition and patterned by reactive ion etching on a quartz glass substrate. The core was 10 μm wide, 8 μm high and 64.5 mm long, which permitted single-transverse-mode laser oscillation. The threshold pump power for CW oscillation was 150~200 mW at a pumping wavelength of 0.98 μm.

Generation of 27 fs pulses of 70 kW peak power at 80 MHz repetition rate using a cw self-pulsing Ti:sapphire laser

We have built a self-mode-locked Ti:sapphire cw oscillator delivering up to 2 W of average output power. This oscillator provides 100 fs pulses tunable in the 770–807 nm range. Using a fiber-prism compressor at the cavity output, the pulses have been compressed down to 27 fs at 785 nm, while keeping 200 mW average power.

Phase-conjugation and self-oscillation with copropagating cross-polarized beams

We present the result of an experiment on optical phase conjugation made with a probe beam propagating in the same direction as the forward pump beam but having an orthogonal polarization. Using the difference of polarization, we separate the reflected beam from the backward pump beam. Is is shown that the amplitude of the reflected beam is the sum of two components, one proportional to the conjugate of the probe and one proportional to the amplitude of the probe. The experiment is done in sodium vapor and reflectivities larger than 350% have been observed near the D 1 transition. Weaker reflectivities due to a less efficient optical pumping are obtained near the D 2 line. We also describe the characteristics of the cw oscillation that appears between the Na cell and a mirror.

Modeling of longitudinally pumped CW Ti:sapphire laser oscillators

Longitudinal pumping of CW Ti:sapphire oscillators is considered to predict the power output of such oscillators using folded, astigmatically compensated cavities. The model predicts how the oscillator performance is affected by the selection of Ti/sup 3+/ concentration, material figure of merit, rod length, and pump and cavity mode waists. Experimental results for broadband CW oscillators pumped by CW argon ion lasers are reported, and these are shown to be in excellent agreement with theory. Nearly 30% slope efficiency is achieved with a four-mirror folded cavity and even higher efficiencies are predicted for optimized pumping.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optimum condition for high output power of a coaxial type He-Cd II white light laser.

Optimum conditions for high output power are described concerning a laser operation and a resonator for primary three colors in a coaxial type He-Cd II white light laser. Optimum discharge voltages for three-color operations are quantitatively determined by experimental data obtained from laser oscillation using for some laser tubes with the electrode dimensions designed for a white light laser. A cw white light laser with a 50-cm discharge length is accomplished under the optimum conditions for white light operation. The optimum transmission factors for three colors on the resonator are determined by simulating of laser output power. The simulation is carried out by using the experimental data of spontaneous emission light and lifetimes of the levels for white light oscillation. The results show that when most suitable mirrors are used, a 10-mW white light laser in cw oscillation can be achieved.

High-power and fundamental-mode oscillating flared sba lasers

Flared SBA lasers with a flared waveguide are investigated. A single-lobed far-field pattern (FFP) parallel to the junction in CW oscillation at 25°C is maintained up to 80 mW.

Study on YAG laser chip breaking.

Chip breaking during a finish boring process has previously been a problematic procedure due to a lack of suitable automatic chip breaking methods. This paper presents the novel and automatic chip breaking method that utilizes a YAG laser together with an optical fiber. Preliminary experiments with sample model chips showed that a YAG laser of a CW oscillation mode could cut the model chips for wider ranges of width and thickness than that of a Q-switched mode. Succeeding experiments on an actual turning process revealed that a focused laser beam of more than 104 W/cm2 fully covering the positional fluctuation of generating chips could cut chips satisfactorily. These experimental results were used in the design of a new tool holder with a YAG laser machining optics for finish boring. The tool holder exhibited an excellent performance under the conditions: a machining speed of 60m/min, a depth of cut of 0.05-0.1mm and a feed rate of 0.08-0.2mm/rev. The laser power used was 150 W.

Observation of continuous-wave self-oscillation due to pressure-induced two-wave mixing in sodium.

Collisional damping can induce a coupling between two nonresonant light beams propagating in an atomic vapor. This coupling is sufficiently important to induce a gain process for a weak probe beam interacting with an intense pump beam. We present here the first observation of a cw oscillation generated by this process using a cell which contains sodium and helium, the pump beam being slightly detuned from the ${\mathrm{D}}_{2}$ resonance line. We also show how the self-oscillation due to four-wave mixing is modified by the presence of a buffer gas.

A novel technology for formation of a narrow active layer in buried heterostructure lasers by single-step MOCVD

A new technology of fabricating a buried heterostructure laser with a narrow active layer in a single-step MOCVD process other than the conventional two-step process is proposed. The technology is based on the separate growth on the undercut ridge. The anisotropic growth has been found to be very useful for formation of a very narrow active region in a self-aligned manner. The novel RBH laser implemented by the single-step MOCVD process has been proposed. The RBH laser has exhibited CW lasing oscillation with a threshold current as low as 30 mA at room temperature and with the circular beam spot.

An investigation of the Co:MgF2laser system

The Co:MgF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser, tunable over the range from 1.5 to 2.3 μm, has been investigated under a variety of operating conditions. Included in this paper are reports on basic spectroscopy of Co:MgF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , a determination of the gain cross section, the efficiency and temporal behavior under pulsed excitation, and performance in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -switched mode. In addition, operation with thermoelectric cooling and CW oscillation at the multiwatt power level are discussed. Equations covering laser-pumped lasers are derived and comparisons between experiments and theory are presented.