Multipass Amplifier Research Articles

Analysis of misaligned optics effects on beam pointing stability in dual-pass optical system

The high-power laser device utilizes a multi-pass amplification system to achieve elevated power laser output. Laser beam is transmitted several times through the amplifier, and the pointing stability is a critical factor affecting the efficiency of the system. Any perturbation of the optics during laser transmission can cause misalignment and further lead to beam pointing errors. Laser beam propagation simulation was conducted using the ray tracing method. Equivalent experiment was performed using a laser with a wavelength of 532 nm, and the centroid position data of the laser beam were collected to characterize the effect of the optics misalignment on laser pointing. A model evaluating the sensitivity of the optics was constructed, and the analysis of how various optics impact pointing accuracy was conducted. Results indicate that, a linear relationship exists between the misalignment of the optic and the pointing shift and angular deviation of the beam when a single optic is misaligned. If multiple optics are misaligned, the shift in centroid position of the laser beam can be calculated by adding up the shifts caused by each misaligned optic. Furthermore, the shift in the centroid position of the laser beam is the linear superposition of the misalignment of each optic.

Compact 20-pass thin-disk multipass amplifier stable against thermal lensing effects and delivering 330 mJ pulses with M2 < 1.17.

We report on an Yb:YAG thin-disk multipass amplifier delivering 100 ns long pulses at a central wavelength of 1030 nm with an energy of 330 mJ at a repetition rate of 100 Hz. The beam quality factor at the maximum energy was measured to be M2 < 1.17. The small signal gain is 21.7, and the gain at 330 mJ was measured to be 6.9. The 20-pass amplifier is designed as a concatenation of stable resonator segments in which the beam is alternately Fourier transformed and relay-imaged back to the disk by a 4f-imaging optical scheme stage. The Fourier transform propagation makes the output beam robust against spherical phase front distortions, while the 4f-stage is used to compensate the thermal lens of the thin-disk and to reduce the footprint of the amplifier.

Suppression of nanosecond prepulses from regenerative amplifier and multipass amplifiers in the SULF-1PW laser

Suppression of nanosecond prepulses from regenerative amplifier and multipass amplifiers in the SULF-1PW laser

Power scaling of LED-pumped alexandrite: The road to high gain multipass amplifiers

Our experiment demonstrates that LED-pumping through luminescent concentrator enables sufficient pump power for viable alexandrite amplifier gain. In 10 passes we obtain a gain of 19 with 10 W output power, for 50 µs pulses at 20 Hz and 760 nm.

Thin-disk multi-pass amplifier for kilowatt-class ultrafast lasers

Abstract We report on an improved ytterbium-doped yttrium aluminum garnet thin-disk multi-pass amplifier for kilowatt-level ultrafast lasers, showcasing excellent beam quality. At a repetition rate of 800 kHz, the 6.8 ps, 276 W seed laser is amplified up to an average power of 1075 W, corresponding to a pulse energy of 1.34 mJ. The 36-pass amplifier is designed as a compact mirror array in which the beam alternately propagates between the mirrors and the disk by a quasi-collimated state. We adopted a quasi-collimated propagation to confine stray and diffracted light by the slight curvature of the disk, which enables us to achieve an outstanding extraction efficiency of up to 57% with excellent beam quality in stable laser operation at high power. The beam quality at 1075 W was measured to be M2 &lt; 1.51. Furthermore, stability testing was demonstrated with a root-mean-square power fluctuation of less than 1.67% for 10 min.

Development of a tunable, narrow, and ultraviolet Ce:LiCAF crystal multipass laser amplifier for environmental application

In this paper, the authors present results on the development of both an oscillator and a 4-pass amplifier of ultraviolet and narrow linewidth pulses using a Ce:LiCAF crystal. By using a grating at one end of the laser cavity, the output laser wavelength of the laser can be tuned from 285 nm to 296 nm with a maximum output power of 8 mW at 288.5 nm. Moreover, amplification in a 4-pass amplifier of the Ce:LiCAF laser was investigated theoretically and experimentally. From the results, 49.0 mW amplified pulses can be obtained using a 4-pass amplifier with 7.0 mW power and 3.6 ns pulse duration at 288.5 nm injection, corresponding to an amplifier gain of 7. Furthermore, the angular scattering intensity of some common single-particle aerosols such as black carbon, brown carbon, and polluted water has been studied using the Ce:LiCAF laser. This result can serve as the basis for the multipass laser amplifier’s environmental application, particularly in identifying atmospheric particles.

Propagation and amplification law of undetermined stray light and influence of signal-to-noise ratio in a multipass amplifier system

Multipass amplifier systems in areas such as high-energy-density physics and astrophysics play an important role, but the undetermined stray light caused by defects seriously influencing the output signal-to-noise ratio (SNR) and even resulting in the failure of the main pulse bombardment. In this study, the modulation of nondeterministic stray light caused by the defects in the optical paths of different components in a multipass amplifier system was examined, and a Mie scattering model of multi-crack defects established. Using ray-tracing simulation, the spatial and temporal distribution of stray light was analysed, and experimental verification was conducted. The law of energy amplification for nondeterministic stray light caused by component defect modulation and an empirical formula for the signal to noise ratio of the pre-pulse system were established. This study provides a reference for the accurate troubleshooting of components, optical path defects and an important theoretical basis for the processing and correction of system components.

Demonstration of multi-pass amplification of 46.9 nm laser pumped by capillary discharge

Using a plane–plane resonator composed of silicon carbide mirrors, we achieve for the first time multi-pass amplification of a 46.9 nm laser pumped by capillary discharge. In terms of the temporal characteristics, for an initial argon pressure of 17 Pa, triple-pass amplification of the laser is obtained at a delay time between the pre-pulse and the main pulse currents of 40 µs, and quadruple-pass amplification is obtained at a delay time of 50 µs. The experimental results show that the gain duration of the plasma column is more than 6 ns. In terms of spatial characteristics, the spot of the output laser has a reduced full width at half maximum divergence compared with that from a laser without a resonator.

Measurement of gain-saturation properties of a Q-switched Nd:YAG laser oscillator with a three-pass amplifier and corresponding beam diagnosis

Here, a homemade Q-switched Nd: YAG laser oscillator alongside a three-pass amplifier has been designed and fabricated. The oscillator operates nearly in the fundamental mode and the spot size/phase front curvature is determined by making use of ABCD law regarding the thermal lensing effect. To scale-up the pulse energy in a compact volume, a three-pass amplifier arrangement is coupled to the oscillator. The systematical measurements to obtain the small-signal gain and saturation properties are carried out in terms of various pumping energies. Simultaneously, the output beam from the oscillator and triple-pass amplifier are well diagnosed to determine output energy, pulse duration, spectral width, M2 factor and the radius of curvature. Despite the oscillator pulse giving out 60 mJ, 13 ns however, the output pulse of 800 mJ, 1 Hz, 9 ns at 1064 nm with FWHM 0.024 nm and beam quality factor M2= 2.21 are determined in favor of multi-pass amplifier. Scaling up the pulse energy up to 800 mJ it is shown that the output beam alters its phase front from the initial planar wave to the spherical curvature during the propagation through a multi-pass amplifier due to the elevation of a radial temperature gradient. Eventually, the novelty of this manuscript arises from the effect of energy scale-up on the gain and saturation in laser amplifier and their correlation with the output beam properties.

Dynamics of many-body fragmentation of carbon dioxide dimer tetravalent ions produced by intense femtosecond laser fields

We study experimentally the three-body Coulomb explosion dynamics of carbon dioxide dimer &lt;inline-formula&gt;&lt;tex-math id="M5"&gt;\begin{document}${\rm{(CO_2)}}_{2}^{4+}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M5.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M5.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; ions produced by intense femtosecond laser field. The three-dimensional momentum vectors as well as kinetic energy are measured for the correlated fragmental ions in a cold-target recoil-ion momentum spectrometer (COLTRIMS). Carbon dioxide dimer is produced during the supersonic expansion of &lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}${\rm{(CO_2)_2}}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M6.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M6.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; gas from a 30 μm nozzle with 10 bar backing pressure. The linearly polarized laser pulses with a pulse duration (full width at half maximum of the peak intensity) of 25 fs, a central wavelength of 790 nm, a repetition rate of 10 kHz, and peak laser intensities on the order of &lt;inline-formula&gt;&lt;tex-math id="M8"&gt;\begin{document}${\rm{8 \times10^{14}}}\;{\rm{W/cm^2}}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M8.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M8.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; are produced by a femtosecond Ti:sapphire multipass amplification system. We concentrate on the three-particle breakup channel &lt;inline-formula&gt;&lt;tex-math id="M10"&gt;\begin{document}${\rm{(CO_2)_2^{4+}}} \rightarrow {\rm{CO}}_{2}^{2+}+{\rm{CO^+}}+ {\rm{O^+}}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M10.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M10.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. The two-particle breakup channels, &lt;inline-formula&gt;&lt;tex-math id="M15"&gt;\begin{document}${\rm{(CO_2)_2^{4+}}} \rightarrow {\rm{CO}}_{2}^{2+}+ {\rm{CO_{2}}^{2+}}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M15.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M15.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and &lt;inline-formula&gt;&lt;tex-math id="M19"&gt;\begin{document}${\rm{CO_2^{2+}}\rightarrow CO^++O^+}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M19.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M19.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, are selected as well for reference. The fragmental ions are guided by a homogenous electric field of 60 V/cm toward microchannel plates position-sensitive detector. The time of flight (TOF) and position of the fragmental ions are recorded to reconstruct their three-dimensional momenta. By designing some constraints to filter the experimental data, we select the data from different dissociative channels. The results demonstrate that the three-body Coulomb explosion of &lt;inline-formula&gt;&lt;tex-math id="M20"&gt;\begin{document}${\rm{(CO_2)}}_{2}^{4+}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M20.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M20.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; ions break into &lt;inline-formula&gt;&lt;tex-math id="M21"&gt;\begin{document}${\rm{CO}}_{2}^{2+}+{\rm{CO}}^++{\rm{O}}^+$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M21.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M21.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; through two mechanisms: sequential fragmentation and non-sequential fragmentation, in which the sequential fragmentation channel is dominant. These three fragmental ions are produced almost instantaneously in a single dynamic process for the non-sequential fragmentation channel but stepwise for the sequential fragmentation. In the first step, the weak van der Waals bond breaks, &lt;inline-formula&gt;&lt;tex-math id="M22"&gt;\begin{document}${\rm{(CO_2)}}_{2}^{4+}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M22.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M22.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; dissociates into two &lt;inline-formula&gt;&lt;tex-math id="M23"&gt;\begin{document}${\rm{CO}}_{2}^{2+}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M23.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M23.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; ions; and then one of the C=O covalent bonds of &lt;inline-formula&gt;&lt;tex-math id="M24"&gt;\begin{document}${\rm{CO}}_{2}^{2+}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M24.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M24.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; breaks up, the &lt;inline-formula&gt;&lt;tex-math id="M25"&gt;\begin{document}${\rm{CO}}_{2}^{2+}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M25.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M25.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; ion breaks into &lt;inline-formula&gt;&lt;tex-math id="M26"&gt;\begin{document}${\rm{CO^+}}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M26.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M26.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and &lt;inline-formula&gt;&lt;tex-math id="M27"&gt;\begin{document}${\rm{O^+}}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M27.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M27.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. The time interval between the two steps is longer than the rotational period of the intermediate &lt;inline-formula&gt;&lt;tex-math id="M28"&gt;\begin{document}${\rm{CO}}_{2}^{2+}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M28.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M28.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; ions, which is demonstrated by the circle structure exhibited in the Newton diagram. We find that the sequential fragmentation channel plays a dominant role in the three-body Coulomb explosion of &lt;inline-formula&gt;&lt;tex-math id="M29"&gt;\begin{document}${\rm{(CO_2)}}_{2}^{4+}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M29.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="18-20230699_M29.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; ions in comparison of the event ratio of the two fragmentation channels.

Theoretical and experimental study of ultraviolet broadband laser amplification using Ce:LiCAF crystal

Trivalent cerium ion-doped lithium calcium aluminum fluoride (Ce:LiCAF) crystals have been demonstrated as efficient amplification gain media in the ultraviolet (UV) wavelength region. However, spectral characteristics in the multipass amplification process have not yet been studied theoretically and experimentally. This work investigates the spectral effects, including gain narrowing and spectral shifting using the chromatic Frantz–Nodvik model to simulate the amplification of broadband nanosecond UV pulses from a Ce:LiCAF crystal. From the simulation results, 5.5 mJ amplified pulses can be obtained using a 4-pass amplifier with seed pulses having 0.7 mJ pulse energy, 3 ns pulse duration and 288.5 nm peak wavelength. These values are in good agreement with experimental results. Seed pulses with peak wavelength of 290.0 nm and linewidth of 2.0 nm could be shifted to 289.8 nm peak wavelength and narrowed to 1.9 nm linewidth after 4-pass amplification. Accounting for the spectral effects will enable a more accurate prediction of the amplified pulses’ characteristics, thereby aiding the applications of high-power UV lasers.

Experimental analysis on CPA-free thin-disk multipass amplifiers operated in a helium-rich atmosphere

We present an experimental investigation on the benefits of helium as an atmospheric gas in CPA-free thin-disk multipass amplifiers (TDMPAs) for the amplification to average powers exceeding 1 kW and pulse peak powers reaching 5 GW. Both the performance of the amplifier and the properties of the amplified sub-400 fs laser pulses centred at a wavelength of 1030 nm are compared for different helium concentrations in air, outlining and quantifying the benefits of a helium-rich atmosphere. The amplification of 100 µJ pulses in an atmosphere with 60% helium instead of air led to a maximum increase in efficiency from 24% to 29%. This translated into an increase of average output power and pulse energy of 34 W (i.e +19%) and 0.34 mJ (i.e. +19%) respectively. At the same time an improvement of the beam quality from M2 = 1.18 to M2 = 1.14 was achieved. For the amplification of 10 µJ pulses to over 1 kW of average power an atmosphere with 33% helium led to an improved beam pointing stability by a factor of 2. Moreover, the beam propagation factor M2 improved by 0.1, and the power stability improved by approximately 10%.

Suppressing scattering-induced nanosecond pre-pulses in Ti:sapphire multi-pass amplifiers.

In this Letter, we experimentally investigate a new kind of nanosecond pre-pulse, which originates from the bidirectional scattering of crystals in traditional Ti:sapphire multi-pass amplifiers. The experimental results demonstrate that the intensity of scattering-induced pre-pulses is very sensitive to the scattering angle, and the delay time between the pre-pulse and the main pulse is an integer multiple of the light path in each pass of the amplifier. An optimized multi-pass amplifier configuration is proposed, for what is believed to be the first time, to suppress the scattering-induced pre-pulses. The contrast ratio between pre-pulses and the main pulse is enhanced by more than two orders of magnitude, reaching a level of 10-10. This novel multi-pass amplifier configuration is very simple and economical, and provides an effective solution for the temporal contrast enhancement in the nanosecond range.

LED-pumped Cr:LiSAF laser system operating at 100 Hz based on a multipass amplifier.

The LED-pumping technology is used for the first time, to the best of our knowledge, to develop a complete master oscillator power amplifier (MOPA) system including a multipass amplifier. A pumping head using an original slab architecture is developed integrating a Cr:LiSAF slab pumped by 2112 blue LEDs via a Ce:YAG luminescent concentrator. The slab configuration enables the reaching of a large number of passes-up to 22-together with access to efficient cooling, allowing for a repetition rate scale up. For 22 passes, the amplifier delivers pulses with energy up to 2.4 mJ at 10-Hz repetition rate with a gain of 4.36 at 825 nm. A complete study of the MOPA is described, concluding in nearly constant performances versus the repetition rate, up to 100 Hz.

Thin-disk multipass amplifier delivering sub-400 fs pulses with excellent beam quality at an average power of 1 kW

We present an improved multipass amplifier design, enabling the amplification of ultrashort pulses with excellent beam quality to more than 1 kW of average output power. 260 fs short pulses at an average power of 105 W and a repetition rate of 1 MHz were directly amplified up to an average power of 1033 W. The pulse duration at this power level was measured to be 388 fs assuming a Gaussian temporal shape. This corresponds to a peak power of 2.5 GW. The power stability was measured to be 0.16% RMS over a duration of more than two hours at a sampling rate of 2 Hz. High beam quality is proven with measured values of M x 2 = 1 .16 in the horizontal and M y 2 = 1 .19 in the vertical plane according to ISO Standard 11146.

Design and Thermal Effect Analysis of LD Pumped Er,Yb∶glass Slab Multi-pass Amplifier

Design and Thermal Effect Analysis of LD Pumped Er,Yb∶glass Slab Multi-pass Amplifier

High-power ultrafast thin-disk multipass amplifiers for efficient laser-based manufacturing

Abstract Thin-disk multipass amplifiers represent one of the most powerful approaches to scale the average and peak powers of ultrafast laser systems. The present paper presents the amplification of picosecond and femtosecond pulses to average powers exceeding 2 and 1 kW, respectively. Second-harmonic generation in lithium-triborate crystals with powers higher than 1.4 kW and 400 W at a wavelength of 515 nm with picosecond and femtosecond pulse durations, respectively, are also reported. Furthermore, third-harmonic generation was demonstrated with output powers exceeding 250 W at a wavelength of 343 nm. Finally, processing of silicon, metals, and polycrystalline diamond with fs pulses at an average power of 1 kW is presented to demonstrate removal rates that are improved by orders of magnitude as compared to state-of-the-art techniques.

Azimuthally polarized picosecond vector beam with 1.7 kW of average output power.

We report on a thin-disk multipass amplifier delivering azimuthally polarized, 7.8 ps short, laser pulses at an average power and with pulse energies of up to 1.7 kW and 5.8 mJ, respectively. High polarization purity was achieved by compensating for the arbitrary linear phase shifts that are introduced by tilted optical elements.

Spectral polarization-encoding of broadband laser pulses by optical rotatory dispersion and its applications in spectral manipulation* *Project supported by the National Natural Science Foundation of China (Grant Nos. 92050203, 62075138, 61827815, and 61775142) and Shenzhen Fundamental Research Project (Grant Nos. JCYJ20190808164007485, JCYJ20190808121817100, JSGG20191231144201722, and JCYJ20190808115601653).

We propose a kind of spectral polarization-encoding (SPE) for broadband light pulses, which is realized by inducing optical rotatory dispersion (ORD), and decoded by compensating ORD. Combining with polarization-sensitive devices, SPE can not only work to control polarization-dependent transmission for central wavelength or bandwidth-tunable filtering, but also can be used for broadband regenerative or multi-pass amplification with a polarization-dependent gain medium to improve output bandwidth. SPE is entirely passive thus very simple to be designed and aligned. By using an ORD crystal with a good transmission beyond 3-μm mid-infrared region, e.g., AgGaS2, SPE promises to be applied for the wavelength tuning lasers in mid-infrared region, where the tunning devices are rather under developed compared with those in visible and near-infrared region.

Generation of super strong longitudinal electric field via vector superposition of linearly polarized laser beams

Radially polarized laser beams, which could generate longitudinal electric fields (LEF) in the far field after being focused have drawn increasing interest in wide fields. However, it is difficult to boost a radially polarized laser pulse to high peak power due to its spatially inhomogeneous polarization distribution. Here, we propose a vector superposition approach, firstly partition a linearly polarized beam into two parts in the near field, secondly modulate their polarization direction separately using the electro-optical effect and finally focus them using a high numerical aperture lens, thereby generating the LEF in the far field owing to vector superposition. This approach can amplify a laser pulse to the required peak power by using traditional schemes of the linearly polarized seed-pulse generation and multi-pass amplification, thereby efficiently scaling the LEF to the required magnitude. The simulation results support the theory in concluding that the approach would be a competent way to achieve super strong LEF in the far field of a laser beam.