Amplifier System Research Articles

Simplified design of optical elements for filled-aperture coherent beam combination.

A simplification strategy for segmented mirror splitters (SMS) used as beam combiners is presented. These devices are useful for compact beam division and the combination of linear and 2-D arrays. However, the standard design requires unique thin-film coating sections for each input beam; thus, potential for scaling to high beam-counts is limited due to manufacturing complexity. Taking advantage of the relative insensitivity of the beam combination process to amplitude variations, numerical techniques are used to optimize highly simplified designs with only one, two or three unique coatings. It is demonstrated that with correctly chosen coating reflectivities, the simplified optics are capable of high combination efficiency for several tens of beams. The performance of these optics as beam splitters in multicore fiber amplifier systems is analyzed, and inhomogeneous power distribution of the simplified designs is noted as a potential source of combining loss in such systems. These simplified designs may facilitate further scaling of filled-aperture coherently combined systems in linear array or 2-D array formats.

Nonlinear optical absorption properties of tellurium glasses containing different network modifiers

Linear- and nonlinear-optical absorption and carrier dynamic properties of binary tellurite glasses modified with different amount of WO3, Nb2O5, and ZnO were investigated via UV–Vis spectrophotometer, open aperture Z-scan and pump-probe techniques. Glasses were synthesized using conventional melt quenching technique. The vitreous nature of the samples were confirmed by conducting XRD measurements. The studied glasses have got absorption spectra similar to that of the semiconductor materials and it is found that the absorption edges of the samples blue-shifted with the changing amount and the type of the network modifier. Nonlinear absorption measurements of samples were carried out using a laser source with 532 nm wavelength, 10 Hz repetition rate and 4 ns pulse duration. All of the samples showed nonlinear absorption behavior. The transmission pump-probe spectroscopy experiments were carried out to investigate the ultrafast carrier dynamics of studied glasses with the help of Ti:sapphire laser amplifier optical parametric amplifier system with 100 fs pulse duration. The experiments were established by excitation of glasses with 400 nm pump and 500 nm probe lights. The results of the measurements indicated that the two-photon absorption and two-photon assisted free carrier absorption mechanisms are responsible for the nonlinear optical processes. In the light of obtained linear and nonlinear optical results, it can be easily concluded that these glasses are very useful for LED, optical amplifier, data storage, and laser host applications

2.5 kW Narrow Linewidth Linearly Polarized All-Fiber MOPA With Cascaded Phase-Modulation to Suppress SBS Induced Self-Pulsing

As a major limitation for power scaling of high power narrow linewidth fiber master oscillator power amplifiers (MOPAs), Stimulated Brillouin Scattering (SBS) induced self-pulsing in polarization maintaining (PM) fiber amplifiers is well characterized and analyzed in this paper by comparing different white noise signal (WNS) phase-modulated modes in experiments. It is found that the self-pulsing effect is not observed in the PM-amplifier with single-frequency laser seed injection, and cascaded WNS modulation provides superior self-pulsing suppression than single WNS modulation with similar output linewidth. Moreover, the experimental results indicate that the self-pulsing threshold can hardly be predicted only by the output linewidth or the defined SBS threshold in a WNS phase modulated fiber amplifier system. As self-pulsing is originated from the spectral spikes in WNS modulated system, we theoretically analyzed characteristics of these spikes in different phase-modulation modes. It indicates the spectral peak intensity can be reduced by cascaded modulation, for which self-pulsing can be suppressed. The theoretical predictions agree well with the experimental results. At the same time, in order to suppress the mode instability effect, a plum blossom shaped bending mode selection device is used in this high-power narrow linewidth fiber amplifier system. Finally, a 32 GHz cascaded WNSs modulated, over than 2.5 kW linearly polarized all-fiber amplifier with a slope efficiency of 86.7% is demonstrated. The polarization extinction ratio (PER) is measured larger than 14 dB and the beam quality factor M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> maintains lower than 1.3 in the power scaling process.

High brightness 1018 nm monolithic fiber laser with power scaling to >500 W.

We have studied 1018 nm high power monolithic fiber lasers to be used as pump sources for multi-kilowatt (kW)-level in-band master oscillator power amplifier (MOPA) systems. The performance of the cavity in terms of wavelength selectivity, optical efficiency, and robustness against amplified spontaneous emission (ASE)-induced parasitic lasing is analytically investigated with respect to doped fiber length and cavity parameters. Experimentally, we have demonstrated a 1018 nm fiber laser with an output power of 502 W from a 15/130 µm Yb3+-doped double-cladded fiber, enabling, to our knowledge, the highest reported brightness and radiance density as well. The laser cavity has a slope efficiency of ∼76%, ASE suppression of >50dB, and a near-diffraction-limited beam quality of M2∼1.15. Owing to high brightness with a small core size (i.e., high radiant density), the proposed laser is promising to enable high-power in-band pump integration via fused combiners for multi-kW in-band MOPA systems.

Highly customized 1010 nm, ns-pulsed Yb-doped fiber amplifier as a key tool for on-demand single-photon generation.

The development of highly customized technical devices is a decisive feature of technically complex setups, as frequently observed in quantum experiments. This paper describes the development and realization of an Yb-doped all-fiber amplifier system designed for such a special application, more specifically, an on-demand single-photon source based on four-wave mixing with rubidium Rydberg atoms. The laser is capable of generating bandwidth-limited configurable nanosecond pulses up to peak powers of >100 W and with pulse repetition frequencies (PRF) between 50 Hz and 1 MHz at selectable wavelengths (1008-1024 nm). Especially the amplification of the 1010 nm reference seed at the lower edge of the amplification range for Yb-based fibers is challenging and tends to produce amplified spontaneous emission (ASE) at higher wavelengths. To achieve high ASE suppression, particularly at low pulse repetition frequencies, two acousto-optical modulators (AOM) are utilized both for pulse picking and for temporal filtering. The synchronization between pulse repetition frequency and AOM driver signal allows pulse amplitude fluctuations to be kept below 1%, while ASE is suppressed by at least 85 dB (PRF = 1 MHz) and 65 dB (PRF = 1 kHz).

Enabling high repetition rate nonlinear THz science with a kilowatt-class sub-100 fs laser source.

Manipulating the atomic and electronic structure of matter with strong terahertz (THz) fields while probing the response with ultrafast pulses at x-ray free electron lasers (FELs) has offered unique insights into a multitude of physical phenomena in solid state and atomic physics. Recent upgrades of x-ray FEL facilities are pushing to much higher repetition rates, enabling unprecedented signal-to-noise ratio for pump probe experiments. This requires the development of suitable THz pump sources that are able to deliver intense pulses at compatible repetition rates. Here we present a high-power laser-driven THz source based on optical rectification in LiNbO3 using tilted pulse front pumping. Our source is driven by a kilowatt-level Yb:YAG amplifier system operating at 100 kHz repetition rate and employing nonlinear spectral broadening and recompression to achieve sub-100 fs pulses with pulse energies up to 7 mJ that are necessary for high THz conversion efficiency and peak field strength. We demonstrate a maximum of 144 mW average THz power (1.44 μJ pulse energy), consisting of single-cycle pulses centered at 0.6 THz with a peak electric field strength exceeding 150 kV/cm. These high field pulses open up a range of possibilities for nonlinear time-resolved THz experiments at unprecedented rates.

SNR Model for Generalized Droop With Constant Output Power Amplifier Systems and Experimental Measurements

Submarine optical transmission systems are commonly operated with constant output power amplifiers. The Gaussian Noise (GN) model of propagation was generally developed in the context of constant gain amplification and accounts for amplified spontaneous emission (ASE) noise and nonlinear interference (NLI) noise. Recently, new models have been proposed and developed to predict signal-to-noise ratio (SNR) models for systems with constant output power amplification that account for the phenomenon known as signal droop, or more broadly, generalized droop (GD). Here we describe a GD model within the context of noises as generated in the GN model, and then further including other distributed noise generation such as might occur for crosstalk in multicore optical fibers. The model results in simple expressions for SNR, signal power, and noise powers as a function of the number of identical spans. We provide numerical modeling confirmation of the analytical model for different formats, and experimental transmission data that is fully consistent with the model.

Development of all-fiber coherent beam combining optical system toward higher output of the fiber laser

In this paper, the authors report that they have developed a low-noise and high gain all-fiber using a coherent beam combining (CBC) system. The CBC optical amplifier system has a feature in which only correlated signal light is combined; however, amplified spontaneous emission (ASE) is not added. Hence, the combined output power increases about twice the signal output power. On the other hand, the power of ASE does not change compared to a conventional amplifier. Thus, the gain and the noise figure can be improved compared to the conventional amplifier. In this research, because the excitation wavelength of erbium doped fiber amplifier is 1480 nm, the minimum value of the theoretical noise figure is 5 dB. As an example, the optical amplifier system proposed in this paper had the small-signal gain of 37.25 dB and the noise figure of 5.60 dB, whereas the conventional optical amplifier system had the small-signal gain of 34.26 dB and the noise figure of 7.44 dB. As a result, we successfully decreased the noise figure by 1.84 dB and increased the small-signal gain by 2.99 dB by using the all-fiber CBC optical amplifier system.

Applying Odor Preconcentrator for Enhancing Human Olfaction: Feasibility Study

Introduction The human sense of smell plays important roles in various scenes in everyday life although we are unconscious of the importance in most cases. For example, olfaction provides an alert that lets us notice dangers or risks such as a fire and rotten food. Savory food smells and comfort flower fragrances make our lives richer. However, it is known that the human olfaction deteriorates with our age [1]. There is no device that can improve the deteriorated olfaction whereas impaired vision can be improved using eyeglasses and a hearing aids can improve our audition. The aim of this research project is to develop an olfactory amplifier for humans [2,3]. In chemical analysis, preconcentrators are frequently used to analyze faint chemical substances [4]. We propose to apply this technique to enhance the sensitivity of human olfaction. In the proposed olfactory amplifier system, airborne odor molecules are collected into adsorbent, as in the preconcentrator. When a sufficient amount of odor molecules are collected, the adsorbent is heated to a high temperature to thermally desorb the collected molecules in a short time. The concentrated odors are thus generated. Here we report our new device made with a monolithic silica adsorbent. Results of odor concentration experiments and a sensory test are presented to show that the device can generate a concentrated smell from a faint smell. Method The schematic diagram of our new device that uses a disc-shaped monolithic silica (MonoTrap DSC18, GL Science) as an adsorbent is shown in Figure 1. The cross section of the device is shown in Figure 2. The diameter and thickness of the monolithic silica disk are 10 mm and 1 mm, respectively. This adsorbent is housed in a flow cell which was made by putting a rubber sheet with a hole in the middle between an acrylic plate and a printed circuit board. A meander heater made on the printed circuit board is used for thermally desorbing the collected odor molecules from the monolithic silica disk. Five stainless tubes are attached to the flow cell. Air is sent into the flow cell through the center tube, and is exhausted from the four outer tubes.In the odor concentration experiment, 1.2 ppm 1-butanol vapor packed in a sampling bag was sent into the flow cell at a flow rate of 0.8 L/min for 10 min. The collected gas was desorbed by heating up the monolithic silica to 200 degrees centigrade. Clean air was sent to the flow cell at a flow rate of 20 mL/min to take the concentrated gas out from the flow cell. The concentration of the butanol gas presented from the device was measured using a semiconductor gas sensor (TGS2620, Figaro Engineering) In the sensory test, we prepared liquid apple flavor consisting of nine components. The flavor was diluted by 100 times using liquid paraffin. Eight subjects participated in the sensory test. Each subject was asked to sniff the diluted apple flavor and compare the smell with the smell of the concentrated vapor presented from the odor amplifier device. Results and Discussions Figure 3 shows the response curve of the gas sensor which was exposed to the vapor coming out from the odor amplifier device. The sensor response is defined as the ratio of the sensor resistance in gas to that in air. Its value decreases with the gas concentration. At 20 s from the start of recording the sensor response, the heating was turned on. The pump was activated after 4 s delay from the activation of the heater. The concentration factor calculated from the maximum butanol concentration detected by the gas sensor was 13.1. When the delay was reduced to 0 s, the concentration factor was slightly decreased. Table 1 shows the result of the sensory test. All subjects answered that the vapor presented from the amplifier device had a stronger smell and that the difference in the smell intensity was significant. Seven out of eight subjects even told us that they perceived no smell from the diluted liquid apple flavor. This resulted in their answers to the third question: most subjects told us that the original and concentrated smells were different because they were unable to perceive the original smell. These results show that a sufficient odor amplification effect can be obtained by a concentration factor of approximately 10. Future work will be addressed to enable quicker presentation of concentrated odors. This work was supported in part by JSPS KAKENHI Grant Numbers 19K14947 and 19H02103, and Research Grant from the Okawa Foundation for Information and Telecommunications.

High-power DUV picosecond pulse laser with a gain-switched-LD-seeded MOPA and large CLBO crystal.

We report the generation of a 266 nm deep ultraviolet (DUV) picosecond pulse with an average output power of 14 W by the fourth-harmonic generation (FHG) from two consecutive frequency-doubling stages of a 1064 nm pulse based on a gain-switched-laser-diode (LD)-seeded hybrid fiber/solid-state master oscillator and power amplifier (MOPA) system. Through the gain-switched operation of a narrow-spectral-linewidth distributed-feedback laser diode and by using a Yb-doped fiber and a two-stage ${\rm Nd}:{{\rm YVO}_4}$Nd:YVO4 solid-state amplifier, we achieved an average power of 46.5 W near the Fourier transform limit for a 13 ps pulse with a repetition rate of 200 kHz. The narrow linewidth pulse characteristics enabled highly efficient frequency conversion, and the efficiency of conversion from 532 to 266 nm was 54%, and from 1064 to 266 nm was 31%. The beam quality factor ${M^2}$M2 of the generated DUV pulse was below 1.2. The highly efficient FHG process resulted in appeasing thermal stress caused by nonlinear absorption in the crystal, and more than 5000 h of continuous operation were achieved without any power down or beam profile degradation.

Noise-like pulse generation around 1.3-µm based on cascaded Raman scattering.

Based on cascaded Raman scattering, near-infrared (NIR) noise-like pulses (NLPs) were successfully demonstrated using a Yb-doped fiber amplifier system. Through a nonlinear fiber amplifier using a germanium-zirconia-silica Yb3+-doped single mode fiber as a gain fiber, the fourth-order Stokes wave (4th-SW) can be excited to extend the emission peak of approximately 1.2-µm and a 3-dB bandwidth of approximately 130 nm. To further shift the wavelength more efficiently toward 1.3 µm, filtered NLPs with an emission peak at 1075 nm were adopted as seeded pulses to excite the fifth-order Stokes wave (5th-SW) because of the better conversion efficiency of stimulated Raman scattering without gain competition with Yb-doped fiber. The generated NIR NLPs were shown to be an excellent light source for the photoluminescence emission from three photon absorption of perovskite to illustrate the red shift of the emission peak owing to the reabsorption effect.

Ultrafast thin-disk multi-pass amplifier system providing 1.9 kW of average output power and pulse energies in the 10 mJ range at 1 ps of pulse duration for glass-cleaving applications.

An ultrafast Yb-doped thin-disk multi-pass laser amplifier system with flexible parameters for material processing is reported. We can generate bursts consisting of four pulses at a distance of 20 ns and a total energy of 46.7 mJ at a repetition rate of 25 kHz. In single-pulse operation, 1.5 kW of average output is achieved at 400 kHz when optimizing for a beam quality of M2 = 1.5. Alignment for maximum output power provides 1.9 kW at the same repetition rate. All results are obtained without chirped-pulse amplification in the multi-pass set-up. The application potential of the system is demonstrated exploring its performance in materials processing of dielectrics. Cleaving of 3.8-mm-thick SCHOTT borofloat glass with a velocity of 1200 mm/s is demonstrated with 300 W of input power. Single-pass modification of 30 mm borosilicate glass is enabled with a Bessel beam at 1 kW of average power delivered by four-pulse bursts of an energy of 30 mJ.

Preliminary results on non-linear effects in Au-ion-doped glass materials irradiated by femtosecond laser pulses

Our research was motivated by the specific properties of noble-metal nanoparticles and their wide applications. The resonance frequency for noble-metal nanostructures is in the near-UV and visible spectral ranges, where most of the commercially-available lasers oscillate. This makes these materials attractive candidates for studying their properties in view of efficient applications. We investigated filaments formation in Au-ion-doped glass materials, transparent in the visible range, during irradiation by femtosecond laser pulses. Second harmonic generation in the media was observed as well. This proved the formation of polycrystalline structures inside the media after femtosecond laser radiation. Further, self-phase modulation and continuum were observed. Thus, the nonlinearity of the media is higher than that of glass not doped with noble-metal particles. The nonlinear effects in the samples were investigated in terms of the laser beam parameters. The laser energy applied was between 10 – 40 μJ. The wavelengths used were in the range 240 – 2600 nm, as generated by an optical parametric amplifier system (TOPAS). The regenerative Ti:Sapphire amplified laser system emits at a central wavelength of 800 nm with a pulse duration of 35 fs and 1-kHz repetition rate.

Dual Wavelength Chirped Pulse Regenerative Amplifier Based on Yb&lt;sup&gt;3+&lt;/sup&gt;:LuAlO&lt;sub&gt;3&lt;/sub&gt; Crystal for Terahertz Applications

Compact diode-pumped chirped pulse regenerative amplifier systems with pulse repetition rate of hundreds kilohertz based on Yb 3+ -doped crystals are of practical importance for wide range of applications such as materials processing, medicine, scientific research, etc. The aim of this work was to study the Yb 3+ :LuAlO crystal based dual wavelength chirped pulse regenerative amplifier. Perovskite-like aluminate crystals have unique spectroscopic properties that allowed to use amplifier active element gain spectrum as an amplitude filter for amplified pulse spectrum and even obtained dual wavelength amplification without any additional components. In our work a simple way to obtain dual-wavelength operation of chirped pulse regenerative amplifier by using the active medium gain spectrum as an amplitude filter for the formation of the amplified pulses spectrum demonstrated for the first time to our knowledge. Maximum output power of 5.4 W of chirped pulses (3.8 W after compression) and optical-to-optical efficiency of 22.5 % have been obtained for Yb:LuAP E//b-polarization at 200 kHz repetition rate. Compressed amplified pulse duration was about 708 fs while separate spectral components durations were 643 fs and 536 fs at 1018.3 nm and 1041.1 nm central wavelengths, respectively. Performed investigations show high potential of Yb 3+ :LuAP crystals as active elements of compact diode pumped chirped pulse regenerative amplifiers

30 W single-frequency continuous-wave master oscillator power amplifier laser at 1342 nm.

We present a power-scalable high-power single-frequency continuous-wave 1342 nm master oscillator power amplifier (MOPA) system that consists of a polarized single-frequency 1342 nm LD seed laser, a Raman fiber preamplifier, and a three-stage ${\rm Nd}:{{\rm YVO}_4}$Nd:YVO4 power amplifier. The single-frequency output power of 30 W at 1342 nm is achieved with the beam quality factors ${{\rm M}^{2\:}} = {1}.{26}$M2=1.26, and the power stability for 1 h is better than ${\pm }\;{0}.{5}\% $±0.5%.

Classification of the temperature-dependent gain of an erbium-doped fiber amplifier by using data mining methods

In this study, the experimental results of an erbium-doped fiber amplifier (EDFA) system designed and experimentally installed in the C-band were classified by using data mining methods. The non-linearity of the EDFA gain with temperature is a problem for EDFA designers. For this reason, the wavelength range to be used in the design, the temperature values and change in the input power values of signals coming to the design are not linear with respect to the output power. Data mining method based on different models are proposed to solve this problem. The data set used contains four variables: temperature, wavelength, input power, and output power. The success results of at WEKA software (Waikato environment for knowledge analysis) were compared with 6 different algorithms. As a result of the analysis made, the C4.5 algorithm, which is the decision tree classification technique, obtained 98.4 % close results in experimental results. When the results are evaluated, data mining algorithms can be constructed and validated using larger data sets. This will help the fiber optic data to be quickly understood and easy to design for optical designers in practical applications.

High energy, high brightness picosecond master oscillator power amplifier with output power 65.5 W.

In this article, it is demonstrated the generation of high pulse energy, high beam quality and high brightness mode-locked picosecond pulses from a compact Nd:YVO4 master oscillator power amplifier system. This system mainly consisted of a SESAM mode-locked picosecond seed generator and four-stage multi-pass amplifiers. A pulse picker was adopted prior to power amplifiers to efficiently reduce the pulse repetition rate. The maximum average output power of 65.5 W was obtained with a repetition rate of 496.85 kHz and a pulse duration of 16.9 ps, corresponding to a maximum pulse energy of 131.83 µJ and a peak power of 7.8 MW. While simultaneously, the output beam quality factors along the x axis and the y axis were measured to be Mx 2=1.36 and My 2=1.32, respectively, therefore, a brightness as high as 3.22 × 109 W·cm-2·Sr was achieved. As far as we all know, this is the highest brightness for a picosecond pulsed Nd:YVO4 MOPA laser at 1064 nm.

Design, construction and characterization of a single unit external cavity diode laser coupled tapered amplifier system for atomic physics

In atomic physics experiments, external cavity diode lasers (ECDLs) are often coupled with tapered amplifiers (TPAs) to provide a highly tunable laser source that also has relatively high output power. Usually these systems are mounted on separate baseplates in separate housings, and when the coupling optics are taken into account, the entire system can take up a large amount of optical table space. Here we report the design, construction, coupling and characterization of an ECDL-TPA system where the ECDL, TPA and coupling optics are mounted on a single, enclosable baseplate. During design and construction, thermal management had a strong influence on the final design, therefore thermal measurements and discussion is emphasized. We report that the output power and frequency was stable over the measurement period. The system is composed of commercially available optical components, and readily machined mounting parts. The system exhibits the possibility of further miniaturization for space-limited applications, and portability.

Development of a photoinduced fragmentation ion trap for infrared multiple photon dissociation spectroscopy.

Methods for isomer discrimination by mass spectroscopy are of increasing interest. Here we describe the development of a three-dimensional ion trap for infrared multiple photon dissociation (IRMPD) spectroscopy that enables the acquisition of the infrared spectrum of selected ions in the gas phase. This system is suitable for the study of a myriad of chemical systems, including isomer mixtures. A modified three-dimensional ion trap was coupled to a CO2 laser and an optical parametric oscillator/optical parametric amplifier (OPO/OPA) system operating in the range 2300 to 4000 cm-1 . Density functional theory vibrational frequency calculations were carried out to support spectral assignments. Detailed descriptions of the interface between the laser and the mass spectrometer, the hardware to control the laser systems, the automated system for IRMPD spectrum acquisition and data management are presented. The optimization of the crystal position of the OPO/OPA system to maximize the spectroscopic response under low-power laser radiation is also discussed. OPO/OPA and CO2 laser-assisted dissociation of gas-phase ions was successfully achieved. The system was validated by acquiring the IRMPD spectra of model species and comparing with literature data. Two isomeric alkaloids of high economic importance were characterized to demonstrate the potential of this technique, which is now available as an open IRMPD spectroscopy facility in Brazil.

High Efficiency Half Bridge Class-D Audio Amplifier System With Front-End Symmetric Bipolar Outputs LLC Converter

A high efficiency half bridge class-D audio amplifier (HB-CDAA) system with symmetric bipolar outputs LLC converter as front-end power supply is proposed and studied in this article. Symmetric bipolar outputs LLC converter provides symmetric bipolar outputs for the HB-CDAA system. The operation modes of class-D amplifier system with front-end bipolar outputs LLC converter in an audio frequency cycle are analyzed, and the effects of HB-CDAA on the operation of its front-end bipolar outputs LLC converter in a switching cycle are studied. It is found that class-D audio amplifier produces voltage pumping on bipolar output voltages in both positive and negative audio frequency cycle, which seriously affects the operation and the efficiency of its front-end bipolar outputs LLC converter and class-D amplifier. Soft switching of bipolar outputs LLC converter can be realized both in the positive and negative audio frequency cycle, which improves efficiency of the proposed HB-CDAA system. A 100 W prototype is built and experimental results show that front-end bipolar outputs LLC converter can provide symmetric bipolar outputs, and realize soft switching. The experimental results also show that voltage pumping on bipolar outputs seriously affects efficiency of the LLC converter. Efficiency of the LLC converter will increase with the decrease of voltage pumping.