Special issue—ultrafast and ultraintense mid-infrared laser technology
2021, 50(8): 20210456.
doi: 10.3788/IRLA20210456
In recent years, the emergence and rapid development of tunable mid-infrared new-band ultra-intense ultrashort lasers have opened up a parametric space in the field of strong-field physics that has rarely been explored so far, providing new opportunities to explore new physics, new effects and new applications of ultra-intense ultrashort laser-matter interactions. The development trends and research directions of mid-infrared ultra-intense ultrashort lasers in recent years were summarized in this paper. The four research directions of optical parametric amplification, optical parametric chirp pulse amplification, mid-infrared pulse post-compression and new optical field modulation technology in mid-infrared were analyzed in a comprehensive manner, and the future development trend of mid-infrared ultra-intense ultrashort lasers was also prospected.
2021, 50(8): 20210396.
doi: 10.3788/IRLA20210396
In recent decades, ultra-intense ultrashort pulse is an important trend in the development of laser optics. Especially in the mid-infrared (MIR) band, because the mid-infrared wavelength has greater ponderomotive force and its spectral range contains almost all the molecular "fingerprint" resonance peaks, the research of mid-infrared laser is very important in the fields of strong-field physics, mid-infrared spectroscopy, material processing and biomedical research. At present, there are many mature techniques for pulse shaping and amplification, such as different frequency generation (DFG), chirped pulse amplification (CPA), optical parametric amplification (OPA) and optical parametric chirped pulse amplification (OPCPA). Using optical parametric chirped pulse amplification technology with its advantages of high amplification gain, high signal-to-noise ratio and wide gain bandwidth to amplify the pulse in nonlinear crystals with high nonlinear coefficient has become one of the main means to obtain ultra-short and ultra-intense mid-infrared pulse.This paper summarizes the research progress of generating and amplifying MIR few-cycle pulse in 2-20 μm based on OPCPA , and its applications in strong-field physics, molecular spectrum detection and biomedicine are briefly described.
2021, 50(8): 20210346.
doi: 10.3788/IRLA20210346
There is a absorption peak of water molecular and a transmission window of atmosphere in the 2 μm spectral range, which has important application in space communication, remote sensing detection, environmental monitoring, laser guidance, infrared countermeasure, surgical operation and so on. With the development of Tm-doped and Tm, Ho co-doped laser host materials and mode-locked technologies, ultrashort pulse all solid state oscillator at 2 μm has become one of the research hotspots of laser technology in recent years. In this paper, the Tm-doped laser host materials and the mode-locked technologies in the 2 μm spectral range were systematically analyzed, the latest development of ultrashort pulse all-solid-state Tm-doped oscillators at home and abroad was summarized, and the representative experiments were analyzed and introduced. Finally its development prospect was summaried.
2021, 50(8): 20210355.
doi: 10.3788/IRLA20210355
High-power 2 μm lasers with few-cycle pulse duration have enabled diverse and important applications ranging from nonlinear frequency conversion, laser spectroscopy to medicine. Soliton self-compression is an effective scheme to deliver such pulses, which is driven by a high-power 2 μm laser source with relatively longer pulse duration. In this work, the soliton self-compression process was realized in a large-mode-area photonic crystal fiber(PCF) driven by a mode-locked Ho:YAG thin-disk oscillator, which delivered three-cycle laser pulses at the center wavelength of 2 μm with an average power of 10.2 W. The pulse duration and spectrum of the pulses were measured by a frequency-resolved optical gating(FROG) apparatus, matching well with the simulation results.
2021, 50(8): 20210352.
doi: 10.3788/IRLA20210352
Femtosecond laser sources operating at around 2 μm spectral range support a plethora of applications, especially in high-resolution molecule spectroscopy, synthesis of mid-infrared optical frequency combs, and broadband mid-infrared sources. Cr:ZnS/ZnSe with broad emission bands is an ideal material to support femtosecond pulse generation at around 2 μm spectral range. Femtosecond mode-locked lasers with all-normal dispersion have recently attracted great attention due to their short pulse duration and large output pulse peak power. An operation of femtosecond Kerr-lens mode-locked laser was demonstrated in Cr: ZnS with all-normal dispersion. The laser system delivered stable mode-locked pulses with pump power of 5.1 W, spectral range from 2.0 to 2.7 μm, average power of 660 mW, duration of 37 fs. It is the first time to realize the operation of femtosecond mode-locked solid laser with all-normal dispersion in Cr: ZnS, which have potential applications in high-resolution molecule spectroscopy and generation of broadband mid-infrared sources.
2021, 50(8): 20210368.
doi: 10.3788/IRLA20210368
The mid-IR femtosecond sources based on difference-frequency generation exhibit many attractive features such as wide wavelength tuning range (6-20 μm), wide coverage range (the entire “fingerprint” region), and low system complexity. Ultrafast fiber laser driven mid-IR fs sources have higher system stability for using less spatial light path only in difference-frequency part. In this article, the different fiber nonlinear frequency conversion techniques in difference-frequency generation were reviewed. The methods improving mid-IR pulse power in different-frequency generation process were introduced in detail.
2021, 50(8): 20210350.
doi: 10.3788/IRLA20210350
Since the first use of Kerr lens mode-locked Ti: sapphire laser pumped RTA optical parametric oscillator to achieve mid-infrared femtosecond laser in 1994, with the continuous emergence of high-power near-infrared pump sources and various high-quality nonlinear crystals, the mid-infrared femtosecond optical parametric oscillator had made considerable progress in terms of average power, pulse width, and tuning range in the past two decades, providing diverse application tools for basic scientific research, biomedicine, and national defense security. Mid-infrared femtosecond optical parametric oscillators were divided into two types in this paper: wavelength tunable output type and broadband-spectrum output type. The research progress of these two types of 2-5 µm mid-infrared femtosecond optical parametric oscillators at home and abroad were reviewed respectively. Finally, the further development trend was discussed. In view of the outlook, high-power, high-beam quality mid-infrared femtosecond optical parametric oscillators and high-energy mid-infrared femtosecond optical parametric oscillators are two important development directions.
2021, 50(8): 20210341.
doi: 10.3788/IRLA20210341
Ultrafast doubly resonant optical parametric oscillators (DRO) are widely used in the generation of mid-infrared broadband optical combs and mid-infrared ultrashort pulses. Because the signal and idler lights both oscillate in the optical cavity, DROs exhibit many different features against singly resonant optical parametric oscillators (SRO). One typical feature is the cavity length detuning in degenerate DRO. The DRO would work in non-degenerate, near-degenerate, and totally degenerately states with cavity length detuning. In order to analyze the effect of cavity length detuning on the work state of degeneracy DRO, the cavity length detuning characteristics of DRO pumped with low dispersion femtosecond laser were systematically studied and summarized based on numerical simulation and usual pumping condition. The production reason of the correlation characteristic was analyzed in theory.
2021, 50(8): 20210314.
doi: 10.3788/IRLA20210314
A mid-infrared (MIR) difference-frequency generation(DFG) technique based on the synchronous pulse induction was proposed and implemented, where a high-speed photodiode detector was used to convert the pump optical pulse into an ultrashort electrical signal for driving a high-bandwidth amplitude modulator on a tunable continuous-wave laser, thus leading to the stable timing synchronization between the dual-color pulses. The nonlinear DFG process with synchronous pulse induction was utilized to effectively reduce the pump threshold for the optical parametric down-conversion. Consequently, watt-level MIR ultrashort pulses could be generated with a maximum pump conversion efficiency up to 60%. The central wavelength could be tuned from 3000 to 3175 nm. Thanks to the all-polarization-maintaining fiber architecture, the instability(STD/MEAN) of the average power was as low as 0.07% in one hour, exhibiting a superior long-term stability. Additionally, the optical-electrical-optical conversion was used to implement the high-precision pulse synchronization with the presented scheme, which eliminated the requirement for the complex feedback circuit. The system was thus featured with simple structure, plug-in operation, and strong robustness, which would pave the way to promoting the MIR light source in field applications.
2021, 50(8): 20210436.
doi: 10.3788/IRLA20210436
Due to the wide applications, rare earth ions Tm3+/ Ho3+ doped mid-infrared 2 μm ultrafast laser has become one of the hot research topics in the laser field in the past decade. In this paper, the development progress of mode-locking techniques at 2 μm was firstly reviewed, including active mode-locking techniques and passive mode-locking techniques based on the effects of saturation absorption, Kerr lens, nonlinear polarization rotation, nonlinear optical loop mirror, nonlinear multimode interference. Secondly, the development on Tm3+/ Ho3+ doped solid and fiber mode-locked laser pulse compressions was reviewed from the sides of the laser gain media and dispersion management techniques. Thirdly, the technical routes of realizing Tm3+/ Ho3+ high-power and high-energy ultrafast lasers were summarized. Finally, the development trends for 2 μm ultrafast lasers were concluded and outlooked.
2021, 50(8): 20210336.
doi: 10.3788/IRLA20210336
3 μm wavelength laser is an ideal laser source for high precision laser surgery, and can be an effective pump source for mid-infrared optical parametric oscillations. The mid-infrared laser in 2.7-3 μm band can be obtained by laser diode (LD) directly pumping Er3+-doped crystal, which has advantages of low cost, compact and simple structure. The Er3+doping concentration is generally high to solve the laser self-termination. However, high concentration causes strong light absorption and up-conversion, which could enhance the thermal effect of laser crystal and hinder the improvement of laser output power. The characteristic fluorite structure of low phonon energy CaF2 crystals makes trivalent rare earth ions easily form “clusters”. A laser gain medium with high thermal conductivity can be obtained by lightly doping Er3+ into the CaF2 crystal. In this work, high quality 1.3at.%Er3+: CaF2 laser crystals were successfully grown by temperature gradient method, diode pumped continuous-wave Er3+: CaF2 laser with maximum output power of 2.2 W was achieved, this is the highest output power in the LD end pumped lightly doping crystals. Furthermore, we demonstrated the 2.8 μm laser continuous-wave performance pumped by 1532 nm LD. The research of the LD direct pumped high power laser is expected to promote the development of the long-wavelength mid-infrared laser towards the direction of compact structure and low cost.
2021, 50(8): 20210349.
doi: 10.3788/IRLA20210349
A LD pumped passively Q-switched and Q-switched mode-locked Tm, Ho: LLF laser using graphene oxide as saturable absorber was reported. Using output mirrors with transmittance of 3%, 5% and 9%, the continuous operation characteristics of Tm, Ho: LLF laser were studied. The experimental and simulation results show that the output mirror with 9% transmittance has the best output characteristics. When the maximum pump power is 20 W, the CW output power is as high as 1793 mW. Then, the Q-switched and Q-switched mode-locked characteristics of Tm, Ho: LLF laser were studied by using graphene oxide as saturable absorber under OC with 9%. The experimental results show that when the pump power of 790 nm LD is less than 7.26 W, the laser is in a simple Q-switched state. When the power is greater than 7.26 W, the laser operation enters into a stable Q-switched mode-locked state. When the maximum pump power is 20 W, the maximum output power is 1052 mW, the repetition rate of mode-locked is 53.19 MHz, and the corresponding average single pulse energy is 19.77 nJ. This average single pulse energy is currently the highest level of a 2 μm mode-locked laser. At the same time, it is confirmed that graphene oxide is a promising two-dimensional mode-locked material in high-energy mode-locked lasers.
