Pump Laser Energy Research Articles

Comparative study of the multiple wavelength lasing of nitrogen ions: the role of vibrational level-dependent photoionization

We report on an optical amplification and energy threshold of the two most prominent emission lines, 391.4 and 427.8 nm, of the cavity-less lasing of nitrogen ions pumped by femtosecond laser pulses. It was found that the two transitions both show optical amplification under a low gas pressure condition, while the 391.4 nm emission is barely amplified under high gas pressure. Moreover, the 427.8 nm emission presents a significant lower pump laser energy threshold and a larger gain factor than the 391.4 nm emission. Numerical simulations based on a three-state coupling model suggest that the smaller ionization Franck–Condon factor from the ground state of N2 to the vibrational level ν = 1 in X2Σ g + state of N2+ favors the formation of population inversion corresponding to the 427.8 nm emission. Meanwhile, the competition between the strong field ionization and excitation induced by the pumping laser requires higher laser intensity to acquire the population inversion for the 391.4 nm radiation, leading to a corresponding larger energy threshold.

Influence of pump laser fluence on ultrafast myoglobin structural dynamics.

High-intensity femtosecond pulses from an X-ray free-electron laser enable pump-probe experiments for the investigation of electronic and nuclear changes during light-induced reactions. On timescales ranging from femtoseconds to milliseconds and for a variety of biological systems, time-resolved serial femtosecond crystallography (TR-SFX) has provided detailed structural data for light-induced isomerization, breakage or formation of chemical bonds and electron transfer1,2. However, all ultrafast TR-SFX studies to date have employed such high pump laser energies that nominally several photons were absorbed per chromophore3-17. As multiphoton absorption may force the protein response into non-physiological pathways, it is of great concern18,19 whether this experimental approach20 allows valid conclusions to be drawn vis-à-vis biologically relevant single-photon-induced reactions18,19. Here we describe ultrafast pump-probe SFX experiments on the photodissociation of carboxymyoglobin, showing that different pump laser fluences yield markedly different results. In particular, the dynamics of structural changes and observed indicators of the mechanistically important coherent oscillations of the Fe-CO bond distance (predicted by recent quantum wavepacket dynamics21) are seen to depend strongly on pump laser energy, in line with quantum chemical analysis. Our results confirm both the feasibility and necessity of performing ultrafast TR-SFX pump-probe experiments in the linear photoexcitation regime. We consider this to be a starting point for reassessing both the design and theinterpretation of ultrafast TR-SFX pump-probe experiments20 such that mechanistically relevant insight emerges.

On‐Chip Non‐Volatile Reconfigurable THz Varifocal Metalens

AbstractImplementation of integrated, nonvolatile, and reconfigurable solutions for on‐chip terahertz (THz) metadevices holds great potential for applications in sensing, integrated circuits, and high‐speed communications. This study demonstrates the non‐volatile reconfigurable dynamic manipulation of THz on‐chip metadevices through optical modulation of Ge2Sb2Te5 (GST) and 2π phase shift of metasurfaces. The approach allows for the simultaneous realization of surface plasmons (SPs) excitation, wavefront shaping, and amplitude modulation in a single device. Using the principles of 2D holography, a reconfigurable multilevel THz SP metalens switch with a maximum extinction ratio of 29.9 dB is presented. The focusing intensity of the metalens can be continuously modulated by varying the pump laser energy. The implementation of the approach is further demonstrated by realizing a switchable THz SP varifocal metalens. Reconfigurable, reversible, and repeated switching is achieved through optical and thermal stimuli, resulting in switching contrast ratios of 7.4 dB and −44.4 dB in the amorphous and crystalline states of GST, respectively. The results demonstrate a promising route toward developing non‐volatile, reconfigurable, and energy‐efficient on‐chip THz integrated metadevices. By enabling the dynamic manipulation of THz waves on a single chip, the approach holds significant potential for advancing the field of terahertz‐integrated photonics.

HF02-12 WATT'S IN A NAME? - THE PEOPLE THAT FOCUSED LASER LITHOTRIPSY

You have accessJournal of UrologyCME1 Apr 2023HF02-12 WATT'S IN A NAME? - THE PEOPLE THAT FOCUSED LASER LITHOTRIPSY Sami E Majdalany, David Leavitt, and Naveen Kachroo Sami E MajdalanySami E Majdalany More articles by this author , David LeavittDavid Leavitt More articles by this author , and Naveen KachrooNaveen Kachroo More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003242.12AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Laser applications have been a significant development in urology, revolutionizing urinary stone disease treatment. We sought to examine the pivotal figures associated with laser lithotripsy and understand their contributions to the evolution of this technology. METHODS: A comprehensive literature review was performed using PubMed database, Google Scholar, and texts regarding the discovery, initial trials and advancements in laser lithotripsy. RESULTS: In 1957, Gordon Gould debuted an optical device, Light Amplification for the Stimulated Emission of Radiation (LASER). Theodore Maiman laid the cornerstone for laser lithotripsy in 1960, in a pivotal Nature publication utilizing a ruby crystal medium, the foundation for the first in vitro destruction of urinary calculi by William Mulvaney and Carl Beck, using 50-300J of energy. In 1962, FJ McClung and Robert Hellwarth used ‘Q-switching’ where an attenuator stores energy in a medium until a maximum level was reached. This insight allowed J.E. Geusic in 1964 to develop the first commercially available solid-state laser medium and laser – Neodymium-doped-YAG (Nd: YAG). In 1983, Graham Watson, applied a laser pulse technique demonstrating fragmentation capability of Nd:YAG. Q-switching did not generate adequate energy, so Watson used a flashlamp to pump laser energy in short pulses highlighting calculi fragmentation with minimal energy, whilst using small laser fiber sizes – leading to the creation of the ubiquitous 200μm laser fiber. The lack of power from Nd:YAG to fragment all stone types, propagated the development of holmium (Ho:YAG) laser by the Wellman Center for Photo Medicine at Massachusetts General Hospital – providing a range of laser settings for frequency (Hertz), energy (Joule), and ultimately power (Watt). Although not associated with the invention of laser lithotripsy, these eponyms are the fundamental units of laser. James Prescott Joule, an English physicist, determined the first law of thermodynamics; the conservation of energy. In 1852, he collaboratively created the ‘Joule-Thompson effect’, significantly contributing to the refrigeration industry. Heinrich Hertz, a German physicist, proved the existence of electromagnetic waves. James Watt. a Scottish engineer, invented horsepower in the 18th century and his modification of the steam engine transformed the Industrial revolution. CONCLUSIONS: Laser lithotripsy is constantly improving our management of urinary calculi, fundamentally built upon decades of innovative and collaborative minds. No matter the ‘Watts’ in our arsenal, we must remember the ‘who’ behind them. Source of Funding: None © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e254 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Sami E Majdalany More articles by this author David Leavitt More articles by this author Naveen Kachroo More articles by this author Expand All Advertisement PDF downloadLoading ...

Terahertz beam array generated by focusing two-color-laser pulses into air with a microlens array

Terahertz (THz) radiation from a plasma filament array generated by focusing two-color laser pulses into the ambient air with a microlens array combining a lens is investigated. We observed a linear dependence of far-field collected THz radiation on the number of filaments and separated THz bunches that are less than 1 mm in diameter. These results indicate that the individual plasma filaments contribute incoherently to the entire THz output, which is demonstrated further with our simulation. Furthermore, the dependence of THz output on laser energy shows that the total energy of the THz beam array has not yet reached its saturation point under the conditions of current pump laser energy in our lab, indicating that it is still possible to further improve the THz output by further increasing the pump laser energy. This THz beam array may possibly be used in micro- or sub-millimeter multi-samples for THz imaging or as a stimuli array source for more scientific research in the future.

Cascaded Amplification and Manipulation of Terahertz Emission by Flexible Spintronic Heterostructures

AbstractSpintronic heterostructures consisting of ferromagnetic (FM) and nonmagnetic (NM) have become increasingly important devices for terahertz (THz) pulse generation, named as spintronic THz emitter (STE). The recycling of the laser pump energy is known to have a key impact on further improvement of the THz emission. Here, an efficient and practical approach to enhance and manipulate THz generation based on a cascaded Pt/CoFe/Ta trilayer fabricated on a flexible polyethylene terephthalate (PET) substrate is shown. Considering the refractive index n of PET is ≈1.61 at 1.55 eV and ≈1.75 at THz frequencies, it is anticipated that the femtosecond (fs) laser pulse propagates with a similar group velocity as the generated THz pulse. Therefore, the cascaded design enables all THz emission from each PET/STE propagating almost in‐phase and yields a 1.55 times amplification compared to a single PET/STE. Two proof‐of‐concept demonstrations are experimentally presented. First one, a metasurface can be assembled with the cascaded PET/STE to manipulate the THz signal. Second one, the cascaded PET/STE is used to perform a spectroscopic measurement of riboflavin. These demonstrations highlight the potential of flexible PET/STE for building blocks of advanced functionalities, such as compact THz emitters, THz spectroscopic, and imaging systems.

Characterization of femtosecond laser-induced grating scattering of a continuous-wave laser light in air.

Nanosecond laser-induced grating scattering/spectroscopy (LIGS) technique has been widely applied for measuring thermodynamic parameters such as temperature and pressure in gaseous and liquid media. Recently, femtosecond (fs) laser was demonstrated to induce the grating and develop the fs-LIGS technique for gas thermometry. In this work, we systematically investigated the fs-LIGS signal generation using 35 fs, 800 nm laser pulses at 1 kHz repetition rate in ambient air by varying the pump laser energies, the probe laser powers and the temporal delays between two pump laser pulses. The stability of single-shot fs-LIGS signal was studied, from which we observed that the signal intensity exhibits a significant fluctuation while the oscillation frequency shows a much better stability. A 4.5% precision of the oscillation frequency was achieved over 100 single-shot signals. By using a previously-developed empirical model, the fs-LIGS signals were fitted using nonlinear least-squares fitting method, by which crucial time constants characterizing the signal decay process were extracted and their dependences on the pump laser energy were studied. From the measured results and theoretical analysis, we found that the appropriate range of the overall pump laser energy for reliable fs-LIGS measurements is approximately located within 80 ∼ 300 μJ. The limitations on the accuracy and precision of the fs-LIGS measurements, the origin of destructive influence of plasma generation on the signal generation as well as the electrostriction contribution were also discussed. Our investigations could contribute to a better understanding of the fs-LIGS process and further applications of the technique in single-shot gas thermometry and pressure measurements in various harsh conditions.

Optical Properties of V2O5 Thin Films on Different Substrates and Femtosecond Laser-Induced Phase Transition Studied by Pump-Probe Method.

Vanadium pentoxide can undergo a reversible phase transition by heating above 260 °C; its non-thermal phase transition, as well as ultrafast dynamical processes, is still not known. Here, femtosecond laser-induced phase transition properties in V2O5 thin films were first explored using femtosecond time-resolved pump–probe spectroscopy. The results show that the phase transient processes occur on a 10−15–10−13 temporal scale. The phase transition and recovery properties are dependent on both the substrates and pump laser energy densities. We propose the oxygen vacancies theory to explain the results, and we provide valuable insights into V2O5 films for potential applications.

Short-pulse broadband stimulated Raman scattering in carbon disulfide via resonance cascading.

Cascaded stimulated Raman scattering (SRS) of carbon disulfide (CS2) was investigated by a pulsed Nd:YAG laser with a wavelength of 532 nm. The fourth-order Stokes and second-order anti-Stokes lines were generated when the pump laser energy was about 1.909 mJ in one sample cell (C1) only. However, the same result was obtained in the second sample cell (C2) with a pump energy of 0.883 mJ. At the same time, the fifth-order Stokes line was produced in C2 when the pump energy increased to 1.208 mJ, and the coherent radiation wavelength ranged from 498 to 644 nm. The result was attributed to the resonance enhancement effect, where the frequency difference between the pump laser and the Stokes light emitted from the working medium (CS2) self-matched with the vibrational energy level of C=S, which resulted in the generation of the cascaded broadband SRS. The anti-Stokes SRS was attributed to four-wave mixing. Simultaneously, the pulse durations of the Stokes and anti-Stokes were compressed to about 380 ps by SRS and laser-induced breakdown. The resonance effect not only reduced the threshold, but it also generated broadband and short-pulse SRS.

Study of the effect of temperature on thermophysical properties of ethyl myristate by dual-beam thermal lens technique

One of the components of biodiesels is ethyl myristate and the study and measurement of its thermal parameters are of great importance. The dual-beam laser thermal lens spectroscopy is used for accurate measurement of thermophysical parameters of ethyl myristate. First, to check the accuracy of our optical setup, thermal lens characteristic time, thermal diffusivity and thermal conductivity of carbon disulfide and benzene were measured at 298 K. There was a reasonable agreement between the measured values and the reference values. Then, the effect of temperature changes on thermal diffusivity and thermal conductivity values of ethyl myristate was studied. The results showed that with increasing temperature from 285 to 358 K, thermal diffusivity decreases from 8.75 to 7.45 × 10−8 m2/s, and thermal conductivity from 0.155 to 0.1432 W/mK. It was also shown that by changing in pump laser energy in the range of 0.06–0.12 joules, both thermal diffusivity and thermal conductivity of ethyl myristate are almost constant.

Silicon Nanoantenna Mix Arrays for a Trifecta of Quantum Emitter Enhancements.

Dielectric nanostructures have demonstrated optical antenna effects due to Mie resonances. Previous work has exhibited enhancements in absorption, emission rates and directionality with practical limitations. In this paper, we present a Si mix antenna array to achieve a trifecta enhancement of ∼1200-fold with a Purcell factor of ∼47. The antenna design incorporates ∼10 nm gaps, within which fluorescent molecules strongly absorb the pump laser energy through a resonant mode. In the emission process, the antenna array increases the radiative decay rates of the fluorescence molecules via a Purcell effect and provides directional emission through a separate mode. This work could lead to novel CMOS-compatible platforms to enhance fluorescence for biological and chemical applications.

Heat transfer and thermoregulation within single cells revealed by transient plasmonic imaging

Summary Cells, as the basic unit of life, undergo continuous heat transfer and dissipation during their metabolism, which is related not only to fundamental cellular functions but also massive applications. Unfortunately, thus far, we still know little about the heat transfer properties at the cellular or subcellular levels. Here, we demonstrated a transient microscopic method to measure the heat transfer in single cells. The thermal conductivity of different regions within a single cell shows a wide heterogeneity, and heat transfer in the region near the cell membrane is more active than the central region. However, the median values of thermal conductivity between different individual cells are quite close. A cellular-level heat regulation that responds to environmental temperature is observed in warm-blooded humans and chickens rather than in cold-blooded bullfrogs. According to the temperature-dependent cell metabolism, we proposed a hypothesis for cellular control of heat dissipation, which might be the cellular-level foundation of body thermoregulation.

Investigation of high-energy extracavity Raman laser oscillator and single-pass Raman generator based on potassium gadolinium tungstate (KGW) crystal

Herein, a high-energy all-solid-state extracavity Raman oscillator and a high-energy single-pass Raman generator based on potassium gadolinium tungstate (KGW) crystal are theoretically and experimentally investigated. First, a high-energy 1064 nm nanosecond laser system with a maximum output energy of 7.03 J at a repetition rate of 1 Hz is built as the pumping source for stimulated Raman scattering (SRS). Then, the output spectra and energy of multiorder Stokes lasers from 1.16 to 1.49 μm are gradually detected as the 1064 nm pumping laser energy increases for both Raman laser structures. For the extracavity Raman oscillator, under a pumping energy of 1.8 J, three-order Stokes lasers with a maximum energy of 448 mJ are obtained when the electric field direction of the pumping laser is parallel to the Ng optical axis of the KGW crystal (E∥Ng). Moreover, to obtain a higher output of the Raman laser without damaging the cavity mirrors, a single-pass Raman generator is studied for comparison purposes. As the 1064 nm pumping laser energy of 2.8 J is injected, the measured maximum output energy of a two-order Stokes laser is ~ 676 mJ for the E∥Ng condition; this is the highest Stokes energy output of the nanosecond solid-state Raman lasers to the best of our knowledge.

Synthesis and optical properties of 1-naphthol rhodamine for deep red laser dyes

In this study, we synthesized two asymmetric rhodamine laser dyes based on 1-naphthol (Dye-1 and Dye-2) and investigated their photophysical and laser performances. It was found that the fluorescence emission wavelengths of the two dyes are successfully extended to the deep red region. Compared with Dye-1, the esterification product Dye-2 displays a redshift of ∼8 nm in the maximum absorption wavelength (λabs) and fluorescence emission wavelength (λem). In aprotic solvents, both λabs and λem of Dye-2 red-shift with the increase of solvent polarity, while its fluorescence quantum yield always decreases with the increase of solvent polarity, no matter in protic solvents or aprotic solvents. The results of laser tests indicated that both Dye-1 and Dye-2 have wide laser tuning range and strong laser conversion efficiency in the red region. The laser conversion efficiency is closely relative to the dye concentration and linearly increases with the increase of pump laser energy.

Femtosecond pump-probe studies of atomic hydrogen superfluorescence in flames

We investigate the excited-state dynamics of hydrogen (H) atoms in flames by using a femtosecond (fs) pump-probe scheme and measuring directional emission signals. An approximately 100-fs pump pulse at 205.1 nm excites H atoms through a two-photon process (n = 3 ←← n = 1), which is followed by detection of the forward emission signals induced by a broadband fs probe pulse near 656 nm. Above a certain threshold, we observe a quadratic dependence of the emission signal on the pump laser energy. Moreover, the linewidth of the forward emission signal varies with the probe delay and the probe laser energy. This behavior can be explained in terms of superradiance. We perform a theoretical analysis and compare the experimental results with the theory, and conclude that, within the conditions of our experiment, the behavior of the atomic system involves atomic coherence, which is produced non-adiabatically and corresponds to a superradiant process. Variations in the duration of the gain time window and lifetime of the excited-state H atoms in flames are explored at different flame conditions (i.e., equivalence ratio and heights above the burner). The fs pump-probe technique demonstrated here can also be extended to characterize the time-resolved population dynamics and the corresponding collisional energy transfer rates for energy levels involved in laser-induced fluorescence detection of H atoms in flames relevant to practical combustion applications.

Photoinduced carrier dynamics in bulk ZnTe using optical-pump terahertz-probe spectroscopy

We have utilized optical-pump terahertz-probe spectroscopy to analyze the relaxation process of photoinduced nonequilibrium carriers in bulk ZnTe with a crystal orientation of ⟨ 110 ⟩ . The experimental results showed that the concentration of nonequilibrium carriers increases with the increase in the energy of pump laser. When the pump energy calculated by a single exponential fitting function reached 63 μJ, the concentration of nonequilibrium carriers attained saturation. In addition, for low pump energy, the relaxation time did not change with increasing pump energy. On the contrary, when the pump energy was high, the relaxation time increased in proportion to the pump laser energy.

Performance analysis and application study of a laser enhancement cavity for photo-neutralization of Negative Ion Beams

Photo-neutralization of negative ion beams is now regarded as a promising concept to enhance plasma heating system efficiency of negative ion based neutral beam injection in large fusion experiments. In this work we describe a photoneutralization scheme currently under test at Consorzio RFX based on the trapping of the second harmonic of a Nd:YAG laser in a closed loop optical cavity. In this work the system performances are analyzed with respect to optical layout and optical losses, in order to identify an optimal configuration, as well as to validate a simple numerical model. The latter is developed to assess the photo-neutralization degree achievable once the system is applied to the NIO1 negative ion beam facility in Padova. In particular, the study defines the requirements of pumping laser energy and repetition rate. A parallel analysis, regarding the application of a resonating enhancement cavity to NIO1, is presented and a comparison between the two approaches is discussed.

Simultaneous generation of controllable double white light lasers by focusing an intense femtosecond laser pulse in air

We report on a simultaneous generation of double white light lasers through filamentation by focusing a femtosecond laser pulse. The appearance of the two white light lasers can be controlled by tilting the focusing lens. The spectral bandwidth and the pulse energy of the double white light lasers were controlled by tuning laser filamenting pulse energy and polarization. Two white light lasers with pulse energies of 1.54 mJ and 1.84 mJ, respectively, were generated with the pump laser energy of 7.43 mJ. Besides being beneficial in understanding the multiple white light lasers generation process through multiple filamentation and its control, the results are also valuable for white light laser-based applications.

Intense sub-terahertz radiation from wide-bandgap semiconductor based large-aperture photoconductive antennas pumped by UV lasers

The characteristics of terahertz (THz) radiation generated from large-aperture photoconductive antennas (LAPCAs) were investigated. The antennas were fabricated using different wide-bandgap semiconductor crystals (ZnSe, GaN, 6H–SiC, 4H–SiC and β–Ga2O3) as the substrate. We used an amplified sub-picosecond KrF excimer laser for illumination of the LAPCAs. THz emission scaling was studied as a function of the bias field and the pump laser energy. It was found that the radiated THz energy scales quadratically as a function of the bias field and sub-linearly as a function of the optical fluence for most of the substrates. Further, we demonstrate that SiC, and especially 4H–SiC LAPCAs offer the best THz generation performances. In order to generate intense THz radiation, we fabricated both 6H- and 4H–SiC LAPCAs with an interdigitated structure. From the field autocorrelation trace, it was found that the spectra lie in the sub-THz regime, extending up to 400 GHz, with a peak frequency at 50 GHz, making the bridge between the microwaves band and the THz band. The maximum generated THz energy was 11 μJ, which is to date the highest THz energy measured from LAPCA sources, with a corresponding peak electric field of 115 kV cm−1 and a corresponding ponderomotive potential of 60 eV. Nonlinear THz experiments were performed using these energetic THz pulses, and open aperture Z-scan experiments in an n-doped InGaAs layer revealed a transmission enhancement of 1.7. It was also shown that in order to have efficient THz generation, the energy contrast of the laser must be kept high.

Development of a Short Pulse Broadband and Narrow Linewidth Ultraviolet Laser Using Ce:LiCAF Crystal

We report the successful development of an all-solid state laser based on a Czochralski method-grown cerium-doped lithium calcium aluminum fluoride (Ce3+:LiCaAlF6 or Ce:LiCAF) crystal as the gain medium. Results for the broadband, narrow linewidth and short pulse laser emission are obtained by pumping the crystal with 7 ns pulses from the fourth harmonics (266 nm) of a Nd:YAG laser operating at 10 Hz. The effects of output coupler reflectivity, resonator length and pump energy on the laser pulse duration were explored. With broadband configuration, a maximum output pulse energy of 3.4 mJ and a slope efficiency of about 33% were achieved. By optimizing the parameters of the resonator and pump laser energy, 450 ps UV laser pulses were generated from resonator transient conditions of low-Q and short resonator under a near threshold pump energy. With narrow linewidth configuration, where the end mirror is replaced by a grating, tunability from 281 nm to 299 nm is also achieved with a linewidth of about 0.2 nm.