Chirped Pulse Research Articles

Supercontinuum generation by saturated second-order nonlinear interactions

We propose a new approach to supercontinuum generation and carrier-envelope-offset detection based on saturated second-order nonlinear interactions in dispersion-engineered nanowaveguides. The technique developed here broadens the interacting harmonics by forming stable bifurcations of the pulse envelopes due to an interplay between phase-mismatch and pump depletion. We first present an intuitive heuristic model for spectral broadening by second-harmonic generation of femtosecond pulses and show that this model agrees well with experiments. Then, having established strong agreement between theory and experiment, we develop scaling laws that determine the energy required to generate an octave of bandwidth as a function of input pulse duration, device length, and input pulse chirp. These scaling laws suggest that future realization based on this approach could enable supercontinuum generation with orders of magnitude less energy than current state-of-the-art devices.

Monolithic tapered Yb-doped fiber chirped pulse amplifier delivering 126 μJ and 207 MW femtosecond laser with near diffraction-limited beam quality

In this work, a high-energy and high peak power chirped pulse amplification system with near diffraction-limited beam quality based on tapered confined-doped fiber (TCF) is experimentally demonstrated. The TCF has a core numerical aperture of 0.07 with core/cladding diameter of 35/250 µm at the thin end and 56/400 μm at the thick end. With a backward-pumping configuration, a maximum single pulse energy of 177.9 μJ at a repetition rate of 504 kHz is realized, corresponding to an average power of 89.7 W. Through partially compensating for the accumulated nonlinear phase during the amplification process via adjusting the high order dispersion of the stretching chirped fiber Bragg grating, the duration of the amplified pulse is compressed to 401 fs with a pulse energy of 126.3 μJ and a peak power of 207 MW, which to the best of our knowledge represents the highest peak power ever reported from a monolithic ultrafast fiber laser. At the highest energy, the polarization extinction ratio and the M2 factor were respectively measured to be ~ 19 dB and 1.20. In addition, the corresponding intensity noise properties as well as the short- and long-term stability were also examined, verifying a stable operation of the system. It is believed that the demonstrated laser source could find important applications in, for example, advanced manufacturing and photomedicine.Graphical

Spectral peak recovery in parametrically amplified THz-repetition-rate bursts.

Multi-photon resonant spectroscopies require tunable narrowband excitation to deliver spectral selectivity and, simultaneously, high temporal intensity to drive a nonlinear-optical process. These contradictory requirements are achievable with bursts of ultrashort pulses, which provides both high intensity and tunable narrowband peaks in the frequency domain arising from spectral interference. However, femtosecond pulse bursts need special attention during their amplification [Optica7, 1758 (2020)10.1364/OPTICA.403184], which requires spectral peak suppression to increase the energy safely extractable from a chirped-pulse amplifier (CPA). Here, we present a method combining safe laser CPA, relying on spectral scrambling, with a parametric frequency converter that automatically restores the desired spectral peak structure and delivers narrow linewidths for bursts of ultrashort pulses at microjoule energies. The shown results pave the way to new high-energy ultrafast laser sources with controllable spectral selectivity.

Evolutionary optimization and long-term stabilization of a white-light seeded two-stage OPCPA seed laser.

Ultrafast laser systems, such as optical parametric chirped pulse amplifiers (OPCPA), are complex tools. Optimizing laser performance for a given application is often plagued by intricate couplings between different output parameters, making simultaneous control of multiple pulse properties difficult. Here, we experimentally demonstrate an autonomous tuning procedure of a white-light seeded two-stage OPCPA using an evolutionary strategy to reliably reach an optimized working point. We use the data collected during the tuning procedure to calibrate a performance model of the laser system, which we then apply to stabilize the intricately coupled laser output energy and spectrum simultaneously. Our approach ensures reliable day-to-day operation at optimized working points without manual tuning. We demonstrate shot-to-shot energy stability of <0.18 % rms, in combination with <25 pm rms wavelength stability and <0.2 % rms bandwidth stability during multi-day operation.

Single-shot, high-repetition rate carrier-envelope-phase detection of ultrashort laser pulses.

We propose a single-shot, high-repetition rate measurement scheme of the carrier-envelope phase offset of ultrashort laser pulses. The spectral fringes resulting from f-2f nonlinear interferometry, encoding the carrier-envelope-phase, are evaluated completely optically via an optical Fourier transform. For demonstration, the carrier-envelope-phase of a 200 kHz, few-cycle optical parametric chirped-pulse amplification (OPCPA) laser system was measured employing an interferometer as a periodic optical filter. The proposed method shows excellent agreement with simultaneous measurement of the spectral fringes by a fast line-scan camera.

Sub-picosecond tunable mid-infrared light source for driving high-efficiency optical rectification.

Optical rectification (OR) is a popular way to generate coherent terahertz radiation. Here, we develop a sub-picosecond mid-infrared (mid-IR) light source with a tailored wavelength and pulse duration for enhancing the OR efficiency. Numerical simulations for a LiNbO3-based OR with tilted pulse-front excitation are first conducted to determine the optimal parameters of pump wavelength and pulse duration, demonstrating that the OR efficiency pumped by 4-µm sub-picosecond (0.5-0.6 ps) pulses is approximately twice the value with 0.8-µm pump at the same conditions. Guided by the simulation results, we build a BaGa4Se7-based optical parametric chirped-pulse amplification system with 1030-nm thin-disk pump and broadband mid-IR seeds. The output performances of >200-µJ pulse energy, ∼600-fs pulse duration and 1-kHz pulse repetition rate are achieved in a spectral range tunable from 3.5 to 5 µm. The large energy scalability and high parameter tunability make the light source attractive to high-efficiency OR in various materials.

Near-infrared spectroscopy of low-transmittance samples by a high-power time-stretch spectrometer using an arrayed waveguide grating (AWG)

Although time-stretch spectroscopy is an emerging ultrafast spectroscopic technique, the applications in industrial fields have been limited due to the low output power caused by undesirable nonlinear effects occurred in a long optical fiber used for pulse chirping. Here, we developed a high-power time-stretch near infrared (NIR) spectrometer utilizing arrayed waveguide gratings (AWGs). The combination of AWGs and short optical fibers allowed large amounts of chromatic dispersion to be applied to broadband supercontinuum pulses without the power limitation imposed by employing the long optical fiber. With the proposed configuration, we achieved chirped pulses with the output power of 60 mW in the 900–1300 nm wavelength region, which is about 10 times higher than conventional time-stretch spectrometers using long optical fibers. With the developed spectrometer, the NIR absorption spectra of a standard material and liquid samples were observed with high accuracy and precision within sub-millisecond measurement time even with four orders of magnitude optical attenuation by a neutral density filter. We also confirmed the quantitative spectral analysis capability of the developed spectrometer for highly scattering samples of an oil emulsion. The qualitative comparison of the measurement precision between the developed spectrometer and the previous time-stretch spectrometer was also conducted.

Research on the control method of the structural stability of the precision tiled-grating

In a chirped pulse amplification device, tiled grating is a key component for compressing ultrashort pulse laser. The control system of the grating tiling device is essential for maintaining the stability of the array grating. In this study, a proportional-integral-derivative algorithm based on the latch compensation method and four-point center difference method is proposed for a truss-type 2 × 1 grating tiling device. Numerical analyses show that this method avoids the saturation loss in the stability control process of the array grating, effectively suppresses noise interference, and ensures the stability of the array grating. The prototype experiment shows that the use of this control algorithm can significantly improve the convergence speed and stability of the grating tiling device. Specifically, compared with a mechanism without a control algorithm, the time to reach the reference position for the first time is reduced by 39.1%, and the stability of the grating device is improved by 58.5%.

417 W, 2.38 mJ Innoslab amplifier compressible to a high pulse quality of 406 fs.

We demonstrate a 417 W, 175 kHz Innoslab chirped pulse amplification laser compressible to short and clean 406 fs pulse duration. A spectral bandwidth (full width at half maximum, FWHM) of ∼3 nm was maintained at full pump power, and the pulses exhibited good pulse quality in a wide tunable pulse energy range from 1.7 mJ to a maximum of 2.38 mJ. At the maximum output power, the compressed pulses were nearly pedestal free. The comprehensive effects of residual high-order dispersion from the front end, the gain shaping effects of the amplifier, and the slight mismatch of third-order dispersion (TOD) between the stretcher (CFBG) and the gating compressor, along with the small nonlinear phase shift accumulated in the amplifier, could have facilitated the high pulse quality. To the best of our knowledge, this is the shortest pulse duration from the Innoslab amplifiers at hundreds of watts average power in the millijoule energy regime.

Compact chirped fiber Bragg gratings for single-photon generation from quantum dots

A scalable source of single photons is a key constituent of an efficient quantum photonic architecture. To realize this, it is beneficial to have an ensemble of quantum emitters that can be collectively excited with high efficiency. Semiconductor quantum dots hold great potential in this context due to their excellent photophysical properties. Spectral variability of quantum dots is commonly regarded as a drawback introduced by the fabrication method. However, this is beneficial to realize a frequency-multiplexed single-photon platform. Chirped pulse excitation, relying on the so-called adiabatic rapid passage, is the most efficient scheme to excite a quantum dot ensemble due to its immunity to individual quantum dot parameters. Yet, the existing methods of generating chirped laser pulses to excite a quantum emitter are bulky, lossy, and mechanically unstable, which severely hampers the prospects of a quantum dot photon source. Here, we present a compact, robust, and high-efficiency alternative for chirped pulse excitation of solid-state quantum emitters. Our simple plug-and-play module consists of chirped fiber Bragg gratings, fabricated via femtosecond inscription, to provide high values of dispersion in the near-infrared spectral range, where the quantum dots emit. We characterize and benchmark the performance of our method via chirped excitation of a GaAs quantum dot, establishing high-fidelity single-photon generation. Our highly versatile chirping module coupled to a photon source is a significant milestone toward realizing practical quantum photonic devices.

Tracking of Gaussian pulse release length inside mode-locked semiconductor laser amplifier

The behavior of the optical pulse release was investigated during chirped pulses amplification, which consisted of two chirped fiber Bragg grating and one semiconductor optical amplifier (SOA). This occurred when the pulse width, &amp;lt;&amp;lt; carrier lifetime , as well as the effect of the length parameter on the shape and spectrum of the electric field, intensity, and phase of amplified pulses, were taken into consideration. The purpose of this research is to investigate the effect of release length on the temporal electric field laser amplifier while simultaneously generating optical pulses with the help of a mode-locked laser system semiconductor. In the scenario where τp and τc are taken into account, we discovered that the length of the release has a significant impact on the modes of the phase and the electric field.

Generation of 35 fs, 20 μJ, GHz pulse burst by hybrid fiber amplification technique.

We have proposed and demonstrated the generation of a high-energy, ultrashort pulse duration, GHz pulse burst polarization-maintaining fiber amplification system that utilizes both chirped-pulse amplification and self-similar amplification techniques. Such hybrid fiber amplification system produces 22 μJ-energy bursts of 200 pulses with a 1.02-GHz intra-burst pulse repetition rate and a 1-MHz inter-burst repetition rate. The center wavelength of the amplified compressed pulse is 1065 nm, with a 3 dB spectral bandwidth of 65 nm. The pulse duration of optimal compression is ∼35 fs, which represents the shortest pulse duration reported to date for any multi-microjoule class amplification system with a repetition rate at the GHz level. At the same time, only common double-cladding Yb3+-doped fiber is used as the gain fiber, without any large-mode-area Yb3+-doped photonic crystal fiber, makes the system compact and reliable by the simple fusion operation.

From design to realization of high diffraction efficiency Littrow configuration diffraction gratings based on multilayer dielectric mirrors patterned with electron beam lithography

Diffraction efficiency (DE) and laser-induced damage threshold of Chirped pulse amplification (CPA) system diffraction gratings (DGs) are one of the main limiting factors for the anticipated progress of high peak power lasers. Optimization of a high reflectivity dielectric multilayer ZrO2/SiO2 stack mirror with a DG etched in the top SiO2 layer was carried out employing the Rigorous coupled wave analysis method. Two families of solutions possessing DE > 0.99 over the bandwidth of the 1030 nm wavelength ultrashort laser and withstanding different fabrication margins were identified for the Littrow configuration. DGs were produced and verified experimentally. Structures permitting variation in both the depth of the DG and filling factor without loss in DE were obtained for the 690 nm thick SiO2 layer. While the 770 nm thick layer permitted separation of the two parameters requiring either rigorous control of the DG depth or filling factor. DG realization technology was proposed employing electron beam lithography and inductively coupled plasma reactive ion etching. Measurements of the fabricated structures demonstrated 0.91 DE for the first diffraction order over the 60 nm bandwidth and under a 6° mounting error from the Littrow configuration. Spectral angular reflectance DE simulations and respective measurements indicated quantitative agreement. The work provides an integrated overview of high DE periodic structure numerical optimization and manufacturing roadmap which could be applied for the high-peak-power laser CPA system development.

High power optical frequency comb with 10-19 frequency instability.

Optical frequency combs with more than 10 W have paved the way for extreme ultraviolet combs generation by interaction with inert gases, leading to extreme nonlinear spectroscopy and the ultraviolet nuclear clock. Recently, the demand for an ultra-long-distance time and frequency space transfer via optical dual-comb proposes a new challenge for high power frequency comb in respect of power scaling and optical frequency stability. Here we present a frequency comb based on fiber chirped pulse amplification (CPA), which can offer more than 20 W output power. We further characterize the amplifier branch noise contribution by comparing two methods of locking to an optical reference and measure the out-of-loop frequency instability by heterodyning two identical high-power combs. Thanks to the low noise CPA, reasonable locking method, and optical path-controlled amplifiers, the out-of-loop beat note between two combs demonstrates the unprecedented frequency stability of 4.35 × 10-17 at 1s and 6.54 × 10-19 at 1000 s.

High-order harmonic generation of ZnO crystals in chirped and static electric fields

High harmonic generation in ZnO crystals under chirped single-color field and static electric field are investigated by solving the semiconductor Bloch equation (SBE). It is found that when the chirp pulse is introduced, the interference structure becomes obvious while the harmonic cutoff is not extended. Furthermore, the harmonic efficiency is improved when the static electric field is included. These phenomena are demonstrated by the classical recollision model in real space affected by the waveform of laser field and inversion symmetry. Specifically, the electron motion in k-space shows that the change of waveform and the destruction of the symmetry of the laser field lead to the incomplete X-structure of the crystal-momentum-resolved (k-resolved) inter-band harmonic spectrum. Furthermore, a pre-acceleration process in the solid four-step model is confirmed.

Chirped-Pulse Amplification in an Echo-Enabled Harmonic-Generation Free-Electron Laser

The field of ultrafast science has experienced significant growth over the last decade, largely attributed to advancements in optical and laser technologies such as chirped-pulse amplification and high-harmonic generation. The distinctive characteristics of intense ultrafast free-electron lasers (FELs) have introduced novel prospects for investigating molecular dynamics, as well as providing an opportunity to gain deeper insights into nonlinear processes in materials. Therefore, high-power ultrafast FELs can be widely used for both fundamental research and practical applications. This study presents a novel approach for producing high-power femtosecond FEL pulses, utilizing chirped-pulse amplification in echo-enabled harmonic generation. Chirped seed pulses are employed to induce frequency-chirped energy modulation in the electron beam. The generated FEL pulse, which inherits the chirped frequency, can be compressed through the gratings in the off-plane mount geometry to provide ultraintense ultrafast pulses. The numerical modeling results indicate that peak power exceeding 20 GW and a pulse duration in the order of several femtoseconds can be achieved.

Detection of ethynylbenzene in TMC-1 and the interstellar search for 1,2-diethynylbenzene

Aims. We investigate the outcome of an electrical discharge of naphthalene and search for the resulting products in the Taurus Molecular Cloud (TMC-1). Methods. Using chirped pulse Fourier transform microwave spectroscopy paired with an electric discharge source, we investigated products resulting from the naphthalene discharge. Quantum chemical calculations were used to help assign species and investigate potential reaction pathways relevant to the interstellar medium. These products were searched for in TMC-1 using the QUIJOTE line survey, covering 31.0-50.3 GHz. Results. We confirm the detection of ethynylbenzene in TMC-1, and we also present a new molecular species, 1,2-diethynylbenzene, which could play an important role in the formation of naphthalene. Over ten products have been identified as resulting from the discharge, with only one of these species found in a previous IR-UV discharge study of naphthalene. Conclusions. Ethynylbenzene has definitively been detected in TMC-1, and while we have identified a potentially important species for the formation of naphthalene and an exothermic reaction pathway, there is no current indication of its presence in TMC-1.

Long Range RF- Text based Communication System

Abstract: With the growth of the Internet of Things (IoT) and other wireless applications in recent years the need for long-range and low-power communication systems has increased. This issue can be resolved by application of LoRa (Long Range) technology, which offers a long-range, low-power, and dependable communication system. LoRa is a wireless modulation technique derived from Chirp Spread Spectrum (CSS) technology. It encodes information on radio waves using chirp pulses in a way similar to the communication principles used naturally by dolphins and bats. LoRa modulated transmission is robust against disturbances and can be received across large distances. In this paper a study on long-range RF text-based communication utilizing LoRa module is presented

Visible to Mid-IR Supercontinuum Generation in Cascaded PCF-Germanate Fiber Using Femtosecond Yb-Fiber Pump

Broadband supercontinuum (SC) fiber sources covering the mid-IR range have many significant applications, largely due to their compactness, reliability, and ease of use. However, most of the existing SC fiber sources cannot boast of either high reliability or a wide bandwidth. Thus, supercontinuum sources based on silica fibers are robust, but are not capable of generating SC in the mid-IR range. Sources based on soft glasses (tellurite, chalcogenide, etc.) generate broadband SC in the mid-IR range but are not used commercially, due to the poor mechanical and chemical characteristics of such fibers. In this work, we propose a new approach consisting of cascade generation of a supercontinuum sequentially in a silica photonic crystal fiber (PCF) and a germanate fiber. Using a standard ytterbium chirped-pulse amplification (CPA) laser system for pumping, we have demonstrated a supercontinuum in the range of 450–2950 nm in PCF and germanate fiber firmly connected by a standard fusion splicing technique. Further optimization of the cascade pump will make it possible to create a compact and reliable all-fiber SC source from the visible to mid-IR range.

The microwave spectra of the conformers of n-butyl nitrate

The microwave spectrum of n-butyl nitrate was recorded in the 5 to 20 GHz frequency range using broadband chirp and narrowband pulse excitation molecular jet Fourier transform microwave spectrometers. A quantum chemistry structural analysis yielded thirteen stable conformers. Among them, the five most energetically stable conformers were observed in the experimental spectra. The most stable conformer features a butyl chain with an anti-gauche-anti conformation (AGA) where the γ-carbon atom is about 64° out of the nitrate plane. For this conformer, spectra of all 13C and 15N minor isotopologues could be measured. The conformer with a straight butyl chain (AAA), and three other conformers (GAA, GGA, and AGG) were also observed. Accurate rotational constants, centrifugal distortion constants, and 14N nuclear quadrupole coupling constants could be deduced and compared to the theoretical values.