Laser Lifetime Research Articles

Thermal imaging of high power diode lasers subject to back-irradiance

CCD-based thermoreflectance imaging and finite element modeling are used to study the two-dimensional (2D) temperature profile of a junction-down broad-area diode laser facet subject to back-irradiance. By determining the temperature rise in the active region (ΔΤAR) at different diode laser optical powers, back-irradiance reflectance levels, and back-irradiance spot locations, we find that ΔΤAR increases by nearly a factor of three when the back-irradiance spot is centered in the absorbing substrate approximately 5 μm away from the active region, a distance roughly equal to half of the back-irradiance spot FWHM (9 μm). This corroborates prior work studying the relationship between the back-irradiance spot location and catastrophic optical damage, suggesting a strong thermal basis for reduced laser lifetime in the presence of back-irradiance for diode lasers fabricated on absorbing substrates.

Plasma chemistry of the sealed-off slab CO laser active medium pumped by radio-frequency discharge with liquid-nitrogen-cooled electrodes

The long-term time behavior of the output power of a sealed-off cryogenic slab CO laser pumped by a repetitively pulsed RF discharge and operating on the overtone (λ = 2.6–3.5 μm) vibrational−rotational transitions of the CO molecule was studied experimentally. It is shown that adding of an anomalously large amount of oxygen (up to 50% with respect to the CO concentration) to the initial gas mixture CO : He = 1 : 10 leads to a manyfold (by several tens of times) increase in the duration of the laser operating cycle (until lasing failure due to the degradation of the active medium). In this case, the laser life-time without replacement of the active medium reaches 105–106 pulses. Using various diagnostics (including luminescence spectroscopy and IR and UV absorption spectroscopy), regularities in the time-behavior of the concentrations of the main component of the active medium (CO molecules) and the products of plasmachemical reactions (O3, CO2) generated in the discharge gap during the laser operating cycle are revealed. Time correlation between the characteristics of the active medium and the laser output power are analyzed. A phenomenological approach to describing the entirety of plasmachemical, purely chemical, gas-dynamic, and diffusion processes determining the behavior of the laser output characteristics throughout the laser operating cycle is offered.

High-temperature operation of 640 nm wavelength high-power laser diode arrays

We realized the fabrication of a red semiconductor laser array with high optical power and reliability using an AlGaInP-based compound semiconductor. To obtain a high optical output, the semiconductor laser requires high-quality quantum wells. In this work, we improved quantum well layer abruptness by applying high-temperature growth condition to quantum wells. We obtained a very high optical power of 20.1 W with a wavelength of 644 nm under this growth condition using magnesium as a dopant for a p-type layer. As a results, we achieved a high characteristic temperature of 68 K and a high electrical-to-optical (E–O) conversion efficiency 37% at 15 W optical output. When the laser lifetime at a temperature of 35 °C and an optical output power of 6.6 W for operation is defined as the time when the output power decreases to 50%, which is usually used for defining the lifetime of ultra high-pressure (UHP) lamps in projection display, we can estimate the lifetime of this laser to be longer than 10000 h or more.

Long term reliability study and life time model of quantum cascade lasers

Here, we present results of quantum cascade laser lifetime tests under various aging conditions including an accelerated life test. The total accumulated life time exceeds 1.5 × 106 device hours. The longest single device aging time was 46 500 hours without failure in the room temperature aging test. Four failures were found in a group of 19 devices subjected to the accelerated life test with a heat-sink temperature of 60 °C and a continuous-wave current of 1 A. Failure mode analyses revealed that thermally induced oxidation of InP in the semi-insulating layer is the cause of failure. An activation energy of 1.2 eV is derived from the dependence of the failure rate on laser core temperature. The mean time to failure of the quantum cascade lasers operating at a typical condition with the current density of 5 kA/cm2 and heat-sink temperature of 25 °C is expected to be 809 000 hours.

Using ferrule-top opto-mechanical probes as a new tool in VCSEL reliability experiments.

Today, vertical cavity surface emitting lasers (VCSELs) are used in many high-end applications, for which the laser lifetime is a critical parameter. Changes in the spatial distribution of the various emission modes of the VCSEL can be used as an early sign of device degradation, enhancing the speed and detail of failure mode analysis. We have developed a ferrule-top combined atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) probe that can be used to analyze the transverse mode pattern of the 850 nm radiation at a <200 nm spatial resolution. During accelerated lifetime testing, the newly developed method shows that small local changes in the optical output can already be detected before any sign of device degradation is observed with conventional methods.

Quantum dot lasers on silicon substrate for silicon photonic integration and their prospect

In this article, the recent progress of III-V quantum dot lasers on silicon substrates for silicon photonic integration is reviewed. By introducing various epitaxial techniques, room-temperature 1.3-m InAs/GaAs quantum dot laser on Si, Ge and SiGe substrates have been achieved respectively. Quantum dot lasers on Ge substrate has an ultra-low threshold current density of 55.2 A/cm2 at room temperature, which can operate over 60 ℃ in continuous-wave mode. Futhermore, by using the SiGe virtual substrate, at 30 ℃ and an output power of 16.6 mW, a laser lifetime of 4600 h has been reached, which indicates a bright future for the large-scale photonic integration.

Comparative study of suspension plasma sprayed and suspension high velocity oxy -fuel sprayed YSZ thermal barrier coatings

Suspension Thermal Spraying is a relatively new thermal spaying technique to produce advanced thermal barrier coatings. This technique enables the production of much different performance thermal barrier coatings than conventional thermal spraying which uses solid powder as a feedstock material. In this work a comparative study is performed on four different types of thermal barrier coatings sprayed with two different thermal spay processes, suspension high velocity oxy-fuel spraying (SHVOF) and suspension plasma spraying (SPS) using two different water-based suspensions. Tests carried out include microstructural analysis with SEM, porosity analysis using weight difference by water infiltration, thermal conductivity measurements using laser flash analysis and lifetime assessment using thermo-cyclic fatigue tests. The results showed that SPS coatings were much porous and hence showed lower thermal conductivity than SHVOF coatings produced with the same suspension. From the thermo-cycling tests it was observed that the SPS coatings showed a higher lifetime than the SHVOF ones.

The fast polarization modulation based dual-focus fluorescence correlation spectroscopy

We introduce two new alternative experimental realizations of dual focus fluorescence correlation spectroscopy (2fFCS), a method which allows for obtaining absolute diffusion coefficient of fast moving fluorescing molecules at nanomolar concentrations, based on fast polarization modulation of the excitation beam by a resonant electro-optical modulator. The first approach rotates every second linearly polarized laser pulse by 90 degrees to obtain independent intensity readout for both foci, similar to original design. The second approach combines polarization modulation of cw laser and fluorescence lifetime correlation spectroscopy (FLCS) like analysis to obtain clean correlation curves for both overlapping foci. We tested our new approaches with different lasers and samples, revealed a need for intensity cross-talk corrections by comparing the methods with each other and discussed experimental artifacts stemming from improper polarization alignment and detector afterpulsing. The advantages of our solutions are that the polarization rotation approach requires just one pulsed laser for each wavelength, that the polarization modulation approach even mitigates the need of pulsed lasers by using standard cw lasers and that it allows the DIC prism to be placed at an arbitrary angle. As a consequence the presented experimental solutions for 2fFCS can be more easily implemented into commercial laser scanning microscopes.

Fluorescent and laser properties of pyrromethene 567 (PM567) doped into multi-precursors derived gel glasses

In this work, the laser dye PM567 was incorporated into various organically modified silicate gel glasses (ORMOSILs) derived by methyltriethoxysilane (MTES) and vinyltriethoxysilane (VTES) precursors mixed in various ratios. The laser performances of PM567 doped into MTES–VTES-derived ORMOSILs including the laser slope efficiency, threshold and lifetime together with the spectroscopic properties were investigated. Blue-shifts of fluorescent peaks, extended fluorescent lifetime, improved laser efficiency and lifetime of PM567 doped into ORMOSILs derived by mixed precursors of MTES and VTES have been observed, which might related to the microstructures and micro-chemical environment of the dye in ORMOSILs.

Spectral study of the stimulated emission of Nd^3+ in fluorotellurite bulk glass

In this work we present, for the first time to our knowledge, laser emission under wavelength selective laser-pulsed pumping in Nd(3+)-doped TeO(2)-ZnO-ZnF(2) bulk glass for two different Nd(3+) concentrations. The fluorescence properties of Nd(3+) ions in this matrix which include, Judd-Ofelt calculation, stimulated emission cross-section of the laser transition and lifetimes are also presented. The site-selective emission and excitation spectra along the (4)I(9/2)→(4)F(3/2) absorption band show the inhomogeneous behaviour of the crystal field felt by Nd(3+) ions in this fluorotellurite glass which allows for spectral tuning of the laser output pulse as a function of the pumping wavelength. The emission cross-section obtained from the Judd-Ofelt analysis and spectral data (4.9x10(-20) cm(2)) is in fairly good agreement with the value obtained from the analysis of the laser threshold data (4x10(-20) cm(2)).

Broadly tunable (440–670 nm) solid-state organic laser with disposable capsules

An innovative concept of thin-film organic solid-state laser is proposed, with diffraction-limited output and a broad tuning range covering the visible spectrum under UV optical pumping. The laser beam is tunable over 230 nm, from 440 to 670 nm, with a 3 nm full width at half maximum typical spectral width. The structure consists of a compact fixed bulk optical cavity, a polymeric intracavity etalon for wavelength tuning, as well as five different disposable glass slides coated with a dye-doped polymer film, forming a very simple and low-cost gain medium. The use of interchangeable/disposable “gain capsules” is an alternative solution to photodegradation issues, since gain chips can be replaced without realignment of the cavity. The laser lifetime of a single chip in ambient conditions and without encapsulation was extrapolated to be around 107 pulses at a microjoule energy-per-pulse level.

Study of laser lifetime by statistical methods

On the basis of a large amount of experimental data, statistical investigation of the average lifetime of a laser depending on ten input physical laser parameters is carried out. It is found that only three of the parameters have a substantial influence on the laser lifetime. Physical analysis and interpretation of the results are provided.

Focus on lasers and imaging

Focus on lasers and imaging

Highly photo-stable dye doped solid-state distributed-feedback (DFB) channeled waveguide lasers by a pen-drawing technique

Pyrromethene dyes doped polymeric channeled waveguide lasers with permanent DFB structures were fabricated via a novel pen-drawing technique with the patterned polydimethylsiloxane (PDMS) chips fabricated through a casting process as the substrates. With the high resolution dispensers, dye doped high viscosity pre-polymers were written into the PDMS grooves and the cross-section of the channeled waveguides could be controlled by both the polymer composition and the pen-drawing parameters. Highly stable laser output with 4.8 × 10(6) pulses of laser lifetime at 500 Hz of pump repetition rate has been obtained, which is suggested to be among one of the best results of pyrromethene 567 (PM567) up to date.

Catastrophic optical degradation of the output facet of high-power single-transverse-mode diode lasers. 2. Calculation of the spatial temperature distribution and threshold of the catastrophic optical degradation

The temperature distribution and the power threshold during the catastrophic optical degradation arecalculated within the framework of the developed model of the COD of the output facet in high-power single-transverse-mode diode lasers. Comparison of the calculation results and the experiment show the model adequacy. The contribution of different physical mechanisms into the heating of the laseroutput facet is analysed. It is shown that the model under study can help to develop the method for predicting the laser lifetime by the accelerated ageing tests.

Laser NIR lifetime spectrometer with nanosecond time resolution

A laser lifetime spectrometer (fluorometer) for recording the luminescence kinetics in the range 950–1400 nm with a time resolution of 1 ns is described. The performance capabilities of the facility are demonstrated by an example of studying the near-IR luminescence of molecular singlet oxygen 1O2. The fluorometer allows measurements of quenched luminescence of 1O2 with a quantum yield of up to 6 × 10−9.

Development of a 635 nm-Laser Diode Spectrometer for Continuous Monitoring of Amino Nitrogen in the Beet Sugar Industry

The quality of sugar beet is affected by harmful nitrogen compounds. Although nitrogen is one of the essential elements for plants, introduction of excess nitrogen as fertilizer to the soil increases the nitrogen containing compounds in beet which deteriorates the quality of sugar production. Hence, the concentration of soluble nitrogen in beets was monitored as a routine process in the sugar industry. In this work, a low cost, but very long life time laser diode spectrometer, was developed for continuous monitoring of amino nitrogen compounds in sugar beets. A laser diode source emits monochromatic light at 635 nm which is the maximum of absorption spectrum of Cu(II)-glutamine complex. A standard solution of Cu(II) ion and glutamine was prepared at pH = 6.0 to calibrate the laser diode spectrometer. The formation of Cu(II)-glutamine complex was examined at pH = 5.0, 6.0, and 7.0 by a continuous variations method and we found a monovalent complex, Cu(II)(glutamine) at pH = 6.0, and a divalent complex, Cu(II)(glutamine)2 at pH = 7.0. A continuous mixing system with a peristaltic pump and tubing was set for monitoring of harmful nitrogen in beets, besides sugar determination with a polarimeter and Na and K measurement with a flame photometer, synchronously. The calibration of the laser diode spectrometer yielded a linear correlation coefficient of R2 = 0.999. A negative correlation between sugar digestion and amino nitrogen content of sugar beets was found, with a correlation coefficient of R2 = 0.807.

Solid state dye lasers based on LDS 698 doped in modified polymethyl methacrylate

Broad band solid state dye lasers based on LDS 698 doped in modified polymethyl methacrylate (MPMMA) with laser wavelength about 650 nm were demonstrated. It was demonstrated that the fluorescence spectra of LDS 698 in solid host MPMMA displays an obvious blue shift about 50 nm comparing with that in ethanol solution. The dye concentration has great effect on the laser's performance including laser slope efficiency and lifetime. The lifetime increased dramatically with the increase of the LDS 698 concentration. With pump repetition rate of 10 Hz and intensity of 0.1 J/cm(2), the maximum lifetime 300,000 shots corresponding normalized photostability 102 GJ/mol was obtained with LDS 698 at 1.5 x 10(-4)mol/L.

Lifetime extrapolation of 650 nm InGaAlP laser diodes with or without adequate burn-in time

The 650 nm InGaAlP laser diodes are the most popular photonic device in consumer electronics. Some of these lasers do not receive adequate burn-in time before sending downstream to practical applications. Lasers without adequate burn-in time may exhibit decreasing operating current and ageing tests may not generate results that can be used to predict laser lifetime and reliability. This paper presents a unified approach that allows us to predict lifetime of lasers with either increasing or decreasing operating current in short-duration ageing tests. Methods for data processing are illustrated by case examples regarding lifetime extrapolation of the data from a 1000 h ageing test of commercially available 650 nm, InGaAlP, 10 mW lasers.

Thermodynamics and laser luminescence spectroscopy of binary and ternary complexation of Am 3+, Cm 3+ and Eu 3+ with citric acid, and citric acid + EDTA at high ionic strength

The binary complexation of Am 3+, Cm 3+and Eu 3+ with citrate has been studied at I = 6.60 m (NaClO 4), pcH 3.60 and in the temperatures range of 0–60 °C employing a solvent extraction technique with di-(2-ethylhexyl)phosphoric acid/heptane. Two complexes, MCit and MCit 2 3 - , were formed at all temperatures. For the three metal ions, the log β 101 was between 5.9 and 6.2 and log β 102 between 10.2 and 10.6 at 25 °C. The thermodynamic parameters for the Am–Cit system have been calculated from the temperature dependence of the β 101 and β 102 values. Positive enthalpy and entropy values for the formation of both complexes are interpreted as due to the contributions from the dehydration of the metal ions exceeding the exothermic cation–anion pairing. The formation of the ternary complex M(EDTA)(Cit) 4− (M = Cm and Eu) was measured to have large stability constants (log β 111 between 20.9 and 24.4) at 25 and 60 °C. Time resolved laser luminescence spectroscopy and lifetime measurement data validated the nature of the complexes of Eu(III) formed in the presence of Cit and EDTA + Cit in 6.60 m (NaClO 4) solution.