Q-switched thulium-doped fiber laser operating at 1940 nm region using a pencil-core as saturable absorber

Q-switched thulium-doped fiber laser (TDFL) is demonstrated using pencil-core flakes as a saturable absorber (SA) for the first time. The SA was fabricated by exfoliating pencil-core flakes on adhesive tape surface, then repeatedly folded over the tape until the flakes homogenously deposited on the tape. A small piece of the tape is sandwiched between two ferrules and incorporated in TDFL cavity to realize a stable Q-switching pulse train. By increasing the 1552-nm pump power from 389 to 431 mW, the repetition rate of the TDFL increases from 14.95 to 34.60 kHz while the pulse width decreases from 6.70 to 4.69 μs. The maximum pulse energy of 46.05 nJ is generated with repetition rate and pulse width of 21.25 kHz and 6.27 μs, respectively. To the best our knowledge, this is a first demonstration SA from mundane object as alternative to commercial bulk graphite for Q-switched fiber laser.     

Tunable Tm-doped fiber ring laser operating at 1.9 μm band using force-induced fiber grating as wavelength tuner

We report wavelength-tunable operation of a Tm-doped silica fiber laser by using a force-induced long-period fiber grating (LPFG) formed in a fiber ring resonator. The laser output wavelength is tuned by moving the transmission passband that is generated between adjacent resonance wavelengths due to the force-induced LPFG. By changing the grating period around 900 μm, we control the laser output wavelength between 1845 and 1930 nm.     

Tunable single longitudinal mode S-band fiber laser using a 3 m length of erbium-doped fiber

In this paper a tunable single-longitudinal mode (SLM), short-wavelength band (S-band) fiber laser using a conventional erbium-doped fiber (EDF) with a length of 3?m and a step index erbium dopant profile as opposed to the commonly used depressed cladding erbium-doped fiber (DC-EDF) is proposed and demonstrated. The proposed SLM fiber laser has a tuning range of 1496 to 1507?nm in a ring configuration using two 0.15?m of EDF which acts as saturable absorbers (SAs). The highest peak power measured is about ?0.6?dBm at a wavelength range of 1502 to 1507?nm. The measured signal-to-noise ratio (SNR) is approximately 74?dB for the same wavelength range. The line-width of the SLM output is measured to be 140?kHz.     

Semiconductor saturable absorber mirror passively Q-switched fiber laser near 2 μm

A passively Q-switched fiber laser near 2?μm is achieved with a semiconductor saturable absorber mirror (SESAM) as a saturable absorber. Stable Q-switched pulses are generated from an extremely compact setup with a central wavelength of 1958.2?nm. Under the bidirectional pump configuration, the repetition rate of the fiber laser can be widely tuned from 20 to 80?kHz by increasing the pump power at the same time the pulse width decreases from 1?μs to 490?ns. When the incident pump power is 1.3?W, the average output power, the pulse repetition rate, the pulse width, and the highest single pulse energy are 91?mW, 80?kHz, 490?ns, and 1.14?μJ, respectively. To further optimize the system configuration, the pulse width can be reduced to 362?ns when the cavity length is reduced.     

Pulse shaping fiber laser at 1.5 μm

In this paper we present, for the first time to our knowledge, a new pulse shaping technology (modulation schemes for seed laser) used to mitigate pulse narrowing effect and SBS effect in a high energy Er:Yb codoped fiber master oscillator power amplifier system at 1.5 μm to obtain longer pulse duration and higher energy. An average power of over 1.3 W and a pulse energy of over 0.13 mJ were obtained at 10 kHz repetition rate with a pulse duration of 200 ns and near-diffraction-limited beam quality (M(2)<1.2).     

Optimization of diode-pumped doubly QML laser with neodymium-doped vanadate crystals at 1.34 μm

We present a theoretical model for a diode-pumped, 1.34 μm V³⁺:YAG laser that is equipped with an acoustic-optic modulator. The model includes the loss introduced by the acoustic-optic modulator combined with the physical properties of the laser resonator, the neodymium-doped vanadate crystals and the output coupler. The parameters are adjusted within a reasonable range to optimize the pulse output characteristics. A typical Q-switched and mode-locked Nd:Lu_0.15Y_0.85VO₄ laser at 1.34 μm with acoustic-optic modulator and V³⁺:YAG is set up, and the experimental output characteristics are consistent with the theoretical simulation results.     

A generation of 2 μm Q-switched thulium-doped fibre laser based on anatase titanium(IV) oxide film saturable absorber

We demonstrate a Q-switched thulium-doped fibre laser operating at approximately 1935 nm wavelength using anatase titanium(IV) oxide (TiO₂) embedded in polyvinyl alcohol as the passive newly saturable absorber (SA). The film has absorption loss of 3.5 dB and modulation depth of 33%. It is sandwiched between two fibre ferrules in a ring laser cavity to produce self-started pulse train with a repetition rate that is tuned from 30.12 to 36.96 kHz as the 1552-nm pump power is increased from 289 to 485 mW. At maximum pump power, the laser produced a Q-switching pulse train with pulse duration, output power, pulse energy and peak power of 1.91 μs, 11 mW, 0.3 μJ and 146 mW, respectively. These results show that the TiO₂ is a new potential SA material for pulsed laser applications.     

Simulation experiments to generate broadband chaos using dual-wavelength optically injected Fabry–Perot laser

Abstract

Broadband chaos can be generated by beating two wavelengths in a hybrid arrangement of Fabry–Perot (FP) Laser and Fiber ring cavity by injecting dual wavelengths. The bandwidth of generated chaos can be controlled by detuning different modes of FP Laser for beating. The bandwidth of generated chaos increased to many folds depending upon the injected strength and wavelength spacing matched to FP laser modes. The bandwidth enhancement in different simulation experiments conducted is optimized by varying different parameters of FP laser and cavity. The waveforms are analyzed and Lyapunov exponents are calculated in order to validate the existence of high bandwidth non-pulsating chaos.     

An evanescent field absorption gas sensor at mid-IR 3.39 μm wavelength

Trace gases such as H₂O, CO, CO₂, NO, N₂O, NO₂ and CH₄ strongly absorb in the mid-IR (>2.5 μm) spectral region due to their fundamental rotational and vibrational transitions. CH₄ gas is relatively non-toxic, however, it is extremely explosive when mixed with other chemicals in levels as low as 5% and it can cause death by asphyxiation. In this work, we propose a silicon strip waveguide at 3.39 μm for CH₄ gas sensing based on the evanescent field absorption. These waveguides can provide the highest evanescent field ratio (EFR)>55% with adequate dimensions. Moreover, EFR and sensitivity of the sensor are highly dependent on the length of the waveguide up to a certain limit. Therefore, it is always a compromise between the length of the waveguide and EFR in order to obtain greater sensitivity.     

High sensitive detection of nitric oxide using laser induced photoacoustic spectroscopy at 213 nm

Trace level detection of nitric oxide (NO) is of great interest for a wide range of applications such as environment and human health. For this purpose, a high sensitive sensor based photoacoustic spectroscopy (PAS) principle has been developed at our laboratory for detection of NO at very low concentration (ppbV). For optimization of the PAS signal and to achieve higher sensitivity, parametric dependence investigation was carried out where PAS signal dependence on NO gas pressure, cell geometry, buffer gas (Ar, N₂, He), and laser pulse energy used three PAS cells developed locally. The best sensitivity achieved with three cells was 41, 11, 20?ppbv, respectively. It is worth reporting that the best PAS signal to noise ratio was achieved by using a cylindrical cell having three acoustic filters and argon as a buffer gas.     

Two-photon absorption laser assisted device alteration using continuous wave 1,340 nm laser

We report several cases of two photon absorption (TPA) laser assisted device alteration (LADA) using continuous wave (CW) 1,340 nm laser in Si Complimentary Metal-Oxide Semiconductor (CMOS) Integrated Circuits (IC). Two photon absorption using CW 1,340 nm laser in Si was confirmed by photon beam induced photocurrent measurements. TPA LADA showed greater than two times better resolution in critical timing circuit defect localization and debug application, when compared with traditional single photon absorption (SPA) LADA with CW 1,064 nm laser. A simplified analysis on the resolution improvements presented here showed in good agreement with our experimental observations. Further enhancements of this technology are outlined, which we believe will enable this technology for critical timing circuit debug capabilities well into the future generations of Si CMOS Debug applications.     

Continuous-wave lasing at 1.06 μm in femtosecond laser written Nd:KGW waveguides

We report on the buried channel waveguide laser at 1065 nm in Nd:KGW waveguides fabricated by femtosecond laser writing with dual-line approach. A relatively high scanning speed of 0.5 mm/s enables acceptable propagation loss less than 2 dB/cm. The fluorescence emission spectra of Nd³⁺ ions measured shows that the fluorescence properties were well preserved in the waveguide region. A stable continuous wave laser at 1065 nm has been obtained at room temperature in the buried channel waveguides by optical pumping at 808 nm. A maximum output power of 33 mW and a slope efficiency of 52.3% were achieved in the Nd:KGW waveguide laser system.     

Continuous-wave Nd:GYSGG laser at 1.1 μm

We demonstrated a compact and simple continuous-wave (CW) Nd:GYSGG laser with triple-wavelength lines at 1105, 1107 and 1110 nm based on R₂ → Y₆, R₁ → Y₅ and R₁ → Y₆ of the ⁴F_3/2 → ⁴I_11/2 transition. The total output power of the triple-wavelength lines was 480 mW. Moreover, we obtained an efficient CW Nd:GYSGG laser at 1110 nm with the output power of 1560 mW at the pump power of 11.05 W. Those lines at 1058 and 1062 nm were suppressed completely by the simple output mirror of high transmission at 1.06 μm.     

Graphene oxide saturable absorber on golden reflective film for Tm:YAP Q-switched mode-locking laser at 2 μm

A diode-pumped Tm:YAlO₃ (Tm:YAP), solid-state Q-switched mode-locking (QML) laser was achieved for the first time by using a graphene oxide saturable absorber on gold reflective film. A pulse width for mode-locking inside the Q-switch envelope of 2?ns with a repetition rate of 156.25?MHz has been obtained at the central wavelength of 1973?nm (32?nm full width at half maximum). The measured maximum average output power amounts to 464 mW under an incident pump power of 9.52?W. By using graphene oxide saturable absorber on golden reflective film instead of the tail end cavity mirror, we not only achieved a broadened spectral region 2?µm laser, but also deepened the modulation of the QML.     

Quantum-Cascade Lasers Generating at the 4.8-μm Wavelength at Room Temperature

We report on room-temperature generation at the 4.8-μm wavelength in a lattice-matched structure of a quantum cascade laser (QCL) grown on indium phosphide (InP) substrate. Laser heterostructures grown by molecular beam epitaxy (MBE) comprised 30 cascades and were designed to generate at the 4.80 μm wavelength corresponding to an atmospheric transparency window. Experiments demonstrated effective lasing at temperatures from 80 to 300 K on a wavelength coinciding with the calculated value, which confirmed the high quality of interfaces, high precision of layer thicknesses, and high accuracy of active region doping.     

Optical properties of tin in the 2.5 to 40μm region

The optical constantsn andk of evaporated tin deposited on different substrates (potassium bromide and mica-sheet discs) were determined in the 2.5 to 40m region by measuring its transmittance. From these values a second step vveacarried out to determine other physical parameters of tin films. These were the density of conduction electrons,N, the effective collision frequency of the electrons ₀ the plasma frequency, ₀, the velocity on the Fermi surface,V ₀ the effective area of the Fermi surface,A _eff, and the absorption coefficient,A. The energy-loss functions for surface and volume plasmons show sharp peak at 7.69m. These values are compared with those found in earlier work.     

Long-Term Stability of 0.65-μm Radiation Thermometers at NMIJ

Narrow-band radiation thermometers with center wavelengths near 0.65 μm are frequently used as standard thermometers at high temperatures. The long-term stability of ten Topcon 0.65-μm radiation thermometers was assessed at NMIJ by using fixed-point blackbodies and spectral responsivity measurements. Most of the changes are due to shifts in the center wavelength of the interference filters to longer wavelengths. Even when the center wavelengths shifted, the filter widths and transmittances remained quite stable for some radiation thermometers, but one was found for which the bandwidth increased from 15.7 to 17.2 nm and the transmittance decreased by 6%. Three Barr filters were found to be very stable in wavelength. The output signals of 0.65-μm Topcon radiation thermometers were within 2% · year⁻¹ without correcting for the wavelength change and within 0.2% · year⁻¹ after the correction. Keeping the objective lens clean is very important for radiation thermometers. Large output decreases were observed in early 2000 for many radiation thermometers at NMIJ. The output changes were as large as 1% and were recovered by cleaning the objective lens.     

Synthesis and characterization of chalcogenide glasses from the system Ga-Ge-Sb-S and preparation of a single-mode fiber at 1.55 μm

The aim of this work is to study different compositions in the Ga-Ge-Sb-S system for the definition of two compositions compatible with the elaboration of a single-mode fiber at the 1.55 μm telecom wavelength. The variations of the glass transition temperature (T_g), the dilatation coefficient (α) and the refractive index (n) have been studied for two glasses series: Ga_xGe_25−xSb₁₀S₆₅ (series 1), Ga₅Ge_25−xSb₁₀S_60+x (series 2). This study has lead to the choice of the Ga₄Ge₂₁Sb₁₀S₆₅ composition as clad glass for the preparation of the single-mode fiber and Ga₅Ge₂₀Sb₁₀S₆₅ composition as the core. The discrepancies for the studied parameters between the core and clad compositions are the following: Δα < 2%, ΔT_g < 3% and Δn = 5 × 10⁻³. Finally a single-mode fiber has been prepared by the rod in tube technique.     

Dy3+ doped GeGaSbS fluorescent fiber at 4.4 μm for optical gas sensing: Comparison of simulation and experiment

The infrared (IR) fluorescence from Dy³⁺ doped Ga₅Ge₂₀Sb₁₀S₆₅ fibers is investigated in details in order to develop bright IR fiber sources emitting at 4.4 μm for CO₂ sensing purposes. Optical sensing requires intense IR radiation to probe with accuracy gas concentrations by measuring the gas absorption. We developed a specific modeling describing the Dy³⁺ doped GeGaSbS fiber IR output power by simultaneously solving rate equations and propagation equations within the fibers. This modeling allows the determination of the IR fluorescence guided along the fiber as a function of the Dy³⁺ doping concentration, the propagation losses and the fiber geometry. The results of the simulation are successfully compared with experimental data and are further discussed in order to determine the optimal set of fiber characteristics maximizing the IR fiber output emission.     

Electronic characterization of several 100 μm thick epitaxial GaAs layers

Non intentionally doped thick epitaxial GaAs layers, grown by chemical vapour phase epitaxy using a high growth rate, are characterized by different electrical techniques applied on a junction (forward and reverse Current–Voltage characteristics, Current versus time and temperature, Deep Level Transient Spectroscopy, Capacitance–Voltage measurements) in order to detect the defects they contain. Experimental data are coupled with theoretical modelling to determine the electrical characteristics of the layers: type and concentration of the carriers, energy levels and concentrations of the defects, associated minority carrier lifetime. The results obtained indicate that i) the concentration of the residual impurities is in the order of 10¹³ to 10¹⁴ cm⁻³, ii) the layers contain two shallow defects (at 0.12 and 0.21 eV below the conduction band Ec) slightly compensated by a deep defect (at Ec-0.5 eV) and iii) the deep defect is in low concentration (10¹² cm⁻³), resulting in a minority carrier lifetime still limited by the radiative recombination process. Therefore, epilayers obtained using high growth rates exhibit electronic properties very similar to the ones obtained using conventional epitaxial techniques. The good and uniform electronic properties of these layers coupled with the low yield of the fluorescence of GaAs is interesting for high resolution X-ray detection.