Diode-pumped vertical external cavity surface emitting laser at 1 μm

We demonstrated a diode-pumped vertical external cavity surface emitting laser with simple plane-concave cavity. When the pump power at a wavelength of 811.6 nm is 1.5 W, the maximum output power is 40.4 mW at the wavelength of 1005.8 nm. The optical-optical conversion efficiency is 2.7%. .     

Intracavity frequency-doubled green vertical external cavity surface emitting laser

An intracavity frequency-doubled vertical external cavity surface emitting laser(VECSEL)with green light is demonstrated.The fundamental frequency laser cavity consists of a distributed Bragg reflector (DBR)of the gain chip and an external mirror.A 12-mW frequency-doubled output has been reached at 540 nm with a nonlinear crystal LBO when the fundamental frequency output is 44 mW at 1080 nm.The frequency doubling efficiency is about 30%.     

Investigation on achieving the diode-pumped weak line laser at 1.3 μm

In this paper, a continuous-wave (CW) diode-side-pumped Nd:YAlO₃ (Nd:YAP) laser operating at the weak line of 1339 nm has been achieved and investigated. The output of the 1339 nm laser was realized based on the polarization selection and reasonable transmittance design. The relationship between the output powers and resonator lengths of the 1339 nm Nd:YAP laser has been studied and the optimum resonator length was adopted to improve the output power. As high as 31.3 W output power of the a-axis polarized 1339 nm laser has been obtained at the pumping power of 555 W with the optical-optical and slope efficiencies to be 5.6% and 13%, respectively. This work will provide an effective way to obtain the weak line lasers for potential applications in spectroscopy, coherent terahertz generation, etc.     

Spectral beam combining of 2 μm Tm fiber laser systems

Output beams from three independently frequency-stabilized thulium master-oscillator power-amplifier fiber laser systems were spectrally combined using a plane-ruled metal diffraction grating. Two laser channels were frequency-stabilized with guided mode resonance filters and the third was stabilized using a plane-ruled metal diffraction grating. The systems had output wavelengths between 1984 and 2015 nm, each with a spectral width of 100-450 pm and output powers between 40-120 W. The combined beam had powers up to 49 W and was 32% efficient with respect to the launched pump power.     

Graphene-based passively Q-switched 2 μm thulium-doped fiber laser

We demonstrated stable pulses generation at 2 μm in a passively Q-switched thulium-doped fiber laser using a few layer graphene thin film. The maximum output power was 4.5 mW and the single pulse energy was 85 nJ at 53 kHz repetition rate, and the pulse width was about 1.4 μs. The pulse width and the repetition rate of the Q-switched fiber laser can be changed along with the pump power. To the best of our knowledge, this is the first report of graphene saturable absorber for passively Q-switched 2 μm fiber lasers.     

Temperature-dependent absorptance of painted aluminum, stainless steel 304, and titanium for 1.07 μm and 10.6 μm laser beams

We measured the temperature-dependent absorptance of metals (Al, Ti, SS304) for continuous beams from 1.07 μm fiber laser and 10.6 μm CO₂ laser using power sensors and infrared (IR) pyrometers. The absorptance measurements were repeated for metals with three different paint coatings. For measurements at elevated temperatures up to the melting point, integrating sphere is not practical since high temperature radiation from a heated target disturbs weak output from the sphere considerably. Our results provide how each metal, whether coated or uncoated, absorbs the infrared beams as temperature is elevated to a melting point. A polynomial approximation to the measured absorptance of each target is provided for modeling of the laser-metal interaction at elevated temperatures.     

LD end pumped mode locked and cavity dumped Nd:YAP laser at 1.34 μm

We report a LD end pumped actively mode locked, passively Q switched and cavity dumped Nd:YAP laser at 1.34 μm. The dumped output pulse energy of 160 μJ is obtained at a repetition rate of 10 Hz. Passing through a LD end pumped, double-passed Nd:YAP amplifier the pulse energy is amplified to 1.44 mJ. The corresponding amplification factor is 9. Stimulated Raman scattering experiment is taken with a 9 mm long PbWO₄ Raman crystal. Maximum of 20% Raman conversion is reached.     

Narrow line-width resonant cavity enhanced photodetectors operating at 1.55 μm

A method for fabrication of long-wavelength narrow line-width InGaAs resonant cavity enhanced (RCE) photodetectors in a silicon substrate operating at the wavelength range of 1.3-1.6 μm has been developed. A full width at half maximum (FWHM) of 0.7 nm and a peak responsivity of 0.16 A/W at the resonance wavelength of 1.55 μm have been accomplished by using a thick InP layer as part of the resonant cavity. The effects of roughness and tilt of the InP layer surface, and its free carrier absorption, as well as the thickness deviation of the mirror pair on the resonance wavelength shift and the peak quantum efficiency of the RCE photodetectors are analyzed in detail, and approaches for minimizing them toward superior performance are suggested.     

A digital-alloy AlGaAs/GaAs distributed Bragg reflector for application to 1.3μm surface emitting laser diodes

A distributed Bragg reflector (DBR) utilizing the digital alloy Al_0.9Ga_0.1As was grown by using the molecular beam epitaxy (MBE) method for application in 1.3 μm optical communications and compared to the analog-alloy AlGaAs/GaAs DBR. The transmission electron microscopic (TEM) image showed a highly abrupt boundary of AlAs and GaAs, which supports the formation of a digital-alloy Al_0.9Ga_0.1As layer. The measurement showed that the digital-alloy AlGaAs/GaAs DBR had similar reflection spectra with enhanced uniform distribution over the whole substrate surface compared to the analog-alloy one. In the digital-alloy Al_0.9Ga_0.1As/GaAs DBR cavity, the reflection dip position was measured at around 1273 nm and the standard deviation of the distribution of the reflection dip was 1.31 nm in wavelength over 1/4 of a three-inch wafer.     

Investigation of 1.06 μm laser induced plasma in air using optical interferometry

The laser produced plasma in air by Q-switch Nd:YAG pulses with 50 mJ and 7 ns was analyzed using Mach-Zehnder interferometer. The interferograms were taken at various delay times after single pulses induced gas breakdown. The 3D electron density distribution at early times of the plasma is investigated. To determine the 3D electron density distribution of the plasma, the FFT analysis is applied to extract the phase of the reconstructed interferograms and the numerical inverse Abel transformation is used to calculate the refractive index. The results provide an understanding of the electron density temporal and spatial evolution of laser induced plasma in air from 18 ns and up to 100 ns of plasma lifetime.     

Suppression of slow gain recovery in ultralong quantum-dash semiconductor optical amplifier emitting at 1.55 μm

Gain dynamics in two quantum-dash semiconductor optical amplifiers of different lengths emitting in the 1.55 μm region are investigated experimentally and compared. It is shown that slow gain recovery due to total carrier relaxation is totally suppressed in the ultralong amplifier. Consequently, the 10%-90% gain recovery time is drastically reduced from about 40 ps (short sample) to 10 ps (long one).     

Amplification characteristics measurement of 1.55 μm multi-mode LD

The amplification characteristics of 1.55 μm multi-mode LD are presented experimentally. It demonstrates that nine wavelengths across 1547–1557 nm have a good amplification, the maximum gain of ∼43 dB at 1552.14 nm is obtained with pump power of 130 mW @980 nm, and noise figure of ∼5.6 dB at 1554.3 nm is achieved.     

On plasma surface coupling of 1.06μm laser radiation with copper targets

The thermal coupling coefficient of neodymium glass laser radiation to copper targets was measured as a function of incident laser intensity. It was shown that the addition of a small amount of NaCl on the surface of the copper target can change the coupling coefficient considerably. A tentative explanation for this effect based on the change of plasma properties due to the presence of sodium is offered.     

6.2 W laser-diode end-pumped continuous-wave Nd:YALO3 laser at 1.34 μm

We report a compact and efficient LD end-pumped linearly polarized Nd:YAP laser operating at 1.34 μm. The laser system with different crystal lengths, output couplers and cavity types were compared. Based on optimizing of the pump system and laser cavity, 6.2 W laser radiation at 1341.4 nm with c-axis polarized was achieved, corresponding to an optical conversion efficiency of about 24.8% with respect to the incident pump power. The laser threshold was only about 1.3 W and the optical slope efficiency was up to 27.2%.     

1.55 μm distributed feedback (DFB) lasers subject to strong 1.4 μm optical injection

An experimental analysis of the influence of optical injection at 1.4 μm wavelength into two different commercial 1.55 μm DFB lasers is reported. The results demonstrate the strong dependence of the DFB behaviour on the injection parameters. Complete mode suppression or signal amplification can be obtained by varying the excitation wavelength and/or intensity, suggesting that these devices could be operated as logic ports or signal amplifiers, according to the injected signal.     

Long range surface plasmon polariton waveguides at 1.31 and 1.55 μm wavelengths

We investigate characteristics of gold metal strip waveguides based on long range surface plasmon polaritons (LRSPPs) along thin metal strips embedded in a polymer for practical applications at the telecommunication wavelengths of 1.31 and 1.55 μm. Guiding properties of the gold strip waveguides are theoretically and experimentally evaluated with the limited thickness and width up to ∼20 nm and ∼10 μm, respectively. The lowest propagation loss of ∼1.4 dB/cm is obtained with a 14.5-nm-thick and 2-μm-wide gold strip at 1.55 μm. With a single-mode fiber, the lowest coupling loss of ∼0.4 dB/facet is achieved with a 14.5-nm-thick and 5-μm-wide gold strip at 1.55 μm. The lowest insertion losses are obtained 8-9 dB with 1.5 cm-long gold strips of a limited thickness and width at both the wavelengths. We demonstrate a 10 Gbps optical signal transmission via the LRSPP waveguide with a 14 nm-thick, 2.5 μm-wide, and 4 cm-long gold strip. These LRSPP waveguides have potential applications for optical interconnects and communications.     

Tm–Ho codoped fiber based all fiber amplification of a gain-switched 2 μm fiber laser

A Tm–Ho codoped fiber amplifier system is built. And, amplification of a gain-switched Tm–Ho codoped fiber laser is investigated. Average output of 300 mW is obtained at repetition rate of tens of kHz with an amplification gain bigger than 11 dB. And, pulse amplification efficiency of resonantly pumped Tm–Ho codoped single clad fiber is comparable with 793 nm pumped Tm-doped double clad fiber. The maximal pulse energy generated is about 13.1 μJ, corresponding to a peak power of 282 W at 20 kHz. During the amplification process, gain-switching, partially modulated gain-switched mode-locking and 100% modulated gain-switched mode-locking are observed sequentially. At gain-switching mode, the laser output enjoys a narrow linewidth of 0.31 nm, while at gain-switched mode-locking mode, the spectral linewidth broadens to 0.6 nm.     

Fast photovoltaic characteristic of silver nano-cluster doped ZnO thin films induced by 1.064 μm pulsed laser

Fast photovoltaic characteristic was found from silver nano-cluster doped ZnO thin films when it was irradiated by 1.064 μm infrared laser. Its arising time is about 1 ns with an open-circuit photovoltage of ∼2 ns full width at half-maximum. A transient photovoltaic signal of ∼80 mV occurred with a full width at half-maximum of about 2 ns was observed under the illumination of a 4 mJ pulsed laser in duration of 25 ps. This fast photovoltaic response perhaps relate to the non-uniform distribution of the silver clusters along direction perpendicular to ZnO surface.     

Self-broadening coefficients and positions of acetylene around 1.533 μm studied by high-resolution diode laser absorption spectrometry

The self-broadening coefficients of acetylene at room temperature have been measured for 10 lines in the P branch of the bands of ¹²C₂H₂ and ¹³C¹²CH₂ near 1.533 μm, using a high resolution tunable diode laser spectrometer developed for the Martian space mission PHOBOS-Grunt. The collisional widths are obtained by fitting each recorded line with the Voigt profile as well as the Rautian profile accounting for the collisional Dicke narrowing effect. The standard Voigt model provides slightly smaller broadening coefficients than the Rautian model. Our data are thoroughly compared to the main atmospheric molecule database HITRAN and previous values in various bands of acetylene. Moreover, it is worth noting that a large number of new transitions not listed in the latest HITRAN08 were measured and identified for the first time.     

Continuous-tunable 4.144-4.851 μm twin-MgO:PPLN cascaded optical parametric generator pumped by a 1.342 μm Nd:GdVO4 laser

An all-solid-state mid-infrared optical parametric generator with wide tunability by using multi-grating periodically poled 5 mol.-% MgO-doped lithium niobate (MgO:PPLN) is reported. The pump source is a diode-pumped Q-switched Nd:GdVO₄ laser operated at 1.342 μm with pulse width of 150 ns and repetition rate of 50 kHz. To extend the interaction length, two identical multi-grating MgO:PPLN crystals have been cascaded in the OPG system. When the incident pump average power is 10 W, the obtained maximum idler output power is 340 mW at 4.144 μm. Compared with only using one multi-grating MgO:PPLN crystal, the obtained idler output power increases by 20.1%. 4.144-4.851 μm continuous-tunable idler output is obtained with six grating periods from 29 to 31.5 μm and temperature from 40 to 200 °C. To our knowledge, this is the first time to use 1.342 μm laser as the pump source of OPG.