Stacking chirped pulse optical parametric amplification

Stacking chirped pulse optical parametric amplification based on a home-built Yb³⁺-doped mode-locked fiber laser and an all-fiber pulse stacker has been demonstrated. Energic 11 mJ shaped pulses with pulse duration of 2.3 ns and a net total gain of higher than 1.1 × 10⁷ at fluctuation less than 2% rms are achieved by optical parametric amplification pumped by a Q-switched Nd:YAG frequency-doubled laser, which provides a simple and efficient amplification scheme for temporally shaped pulses by stacking chirped pulse.     

Short single-mode CO2 laser pulse generation by pulsed Q-switching

A simple method for the generation of short, single-mode CO₂ laser pulses produced by applying two voltage gates (of amplitude 3U_λ/4 and U_λ/4) to an electro-optic Q-switch placed in a three-mirror cavity is proposed. Single, single-mode, well-synchronizable pulses of 3 ns duration and of 3 mJ energy have been experimentally achieved from a TEA CO₂ laser with an intracavity Pockels cell with 3 ns switching time. Using a numerical simulation it is shown that with shorter switching time (≈1 ns) the method enables one to obtain, from such a laser, a single, megawatt pulse of 1 ns duration.     

Single-shot multiple-delay crossed-beam spectral interferometry for measuring extremely complex pulses

We demonstrate a single-shot measurement technique based on spectral interferometry (SI) for measuring the complete intensity and phase vs. time of extremely complex ultrashort laser pulses. Ordinarily, such a method would require an extremely-high-resolution spectrometer, but, by temporally interleaving many SI measurements, each using a different reference-pulse delay, our method overcomes this need. It involves introducing a transverse time delay into the reference pulse by tilting its pulse front transversely to the spectrometer dispersion plane. The tilted reference pulse then gates the unknown pulse by interfering with it at the image plane of a low-resolution imaging spectrometer, yielding an effective increase in the delay range and spectral resolution—by a factor of 30 in our proof-of-principle implementation. Our device achieved a temporal resolution of ~ 130 fs and a temporal range of 120 ps. This simple device has the potential to measure even longer and more complex pulses.     

A Q-switched Nd:YAlO3 laser emitting 1080 and 1342 nm

In this paper, the study of a switchable electro-optic Q-switched Nd:YAlO₃ laser emitting 1080 and 1342 nm wavelength was demonstrated. The two-wavelength lasers were eradiated by a Nd:YAlO₃ crystal pumped by a xenon lamp. Two KD*P Pockels cells were adopted as Q-switches. The output energy of 277.2 mJ at 1080 nm wavelength with a pulse width of 20 ns and that of 190.67 mJ at 1342 nm wavelength with a pulse width of 40 ns was obtained, respectively, in our experiment. By switching on or off the voltages applied to the Pockels cells, the operation of the two-wavelength lasers can be selected in free running mode or Q-switching mode.     

串联式电光开关实现光脉冲宽度大范围可调

为了获得大范围脉宽可调的光脉冲,以连续激光为光源,采用两个外腔调制型电光开关,将该连续激光调制成单脉冲光源.其中两个外腔调制型电光开关采用串联方式工作,两者之间的检偏方向相互垂直,由第一级电光开关实现激光脉冲的快速开启,第二级电光开关实现激光脉冲的快速关闭.通过延时同步机对两个电光开关的动作时间进行控制,从而实现光脉冲宽度大范围可调.实验研究获得了最窄脉冲宽度40 ns,最宽脉冲宽度400 μs的532 nm激光脉冲.     

Selection of CO laser single nanosecond pulse by electro-optic CdTe shutter

To select a single laser pulse from a train of nanosecond pulses emitted by a mode-locked CO laser with wavelengths from ∼5 to 6 μm, an electro-optic shutter based on CdTe Pockels cell was developed. A contrast between the selected pulse and unselected laser emission was equal to 20 and twice as much decreased in a CO laser power amplifier. To increase the contrast, a feasibility of applying a narrow-gap semiconductor as a saturable absorber is discussed.     

串联式电光开关实现光脉冲宽度大范围可调

为了获得大范围脉宽可调的光脉冲,以连续激光为光源,采用两个外腔调制型电光开关,将该连续激光调制成单脉冲光源.其中两个外腔调制型电光开关采用串联方式工作,两者之间的检偏方向相互垂直,由第一级电光开关实现激光脉冲的快速开启,第二级电光开关实现激光脉冲的快速关闭.通过延时同步机对两个电光开关的动作时间进行控制,从而实现光脉冲宽度大范围可调.实验研究获得了最窄脉冲宽度40 ns,最宽脉冲宽度400μs的532 nm激光脉冲.     

KrF激光脉冲整形研究

 实验研究了脉冲堆积法对KrF激光的整形能力。利用受激布里渊散射(SBS)压缩脉冲获得了脉宽为3~5 ns的短脉冲，用4束激光堆积获得了脉宽为10~15 ns、平顶宽度为5~10 ns的整形脉冲。利用实测SBS脉冲数据，对脉冲堆积法进行了数值模拟，模拟的脉冲宽度为12.7 ns，平顶宽度为7.7 ns，该结果与实验相符。对脉冲堆积法的任意整形能力进行了模拟，讨论了脉冲宽度变化对整形的影响，发现脉宽变化在5%以内时，对整形脉冲的影响较小。对整形脉冲的放大进行了定性研究，结果表明：平顶脉冲通过放大器后，前沿部分放大较多，由于饱和作用，后沿放大较少；如果前端整形脉冲前沿为斜坡状，放大后可以得到近平顶的脉冲。     

Generation of 1.5-12 ns width-tunable 532 nm pulses by adopting laser-induced plasma shutter technique

The pulse-shaping technique has found widespread applications in nonlinear optics and material processing. Experimental research on laser-induced plasma shutter to control the 532 nm pulse width is conducted. The impacts of the total pulse output energy on pulse compression are investigated, and a useful conclusion can be drawn that there exists an optimal value of pulse energy at which the shortest output pulse of 3.23 ns can be obtained without a device for delay-time. Once the device for delay-time is employed to change the optical differences between two laser paths, the pulse width can be further shortened to 1.51 ns. In short, the 1.5-12 ns width-tunable 532 nm laser pulses have been obtained by adopting the laser-induced plasma shutter technique.     

Two-color laser desorption of nanostructured MgO thin films

Neutral magnesium atom emission from nanostructured MgO thin films is induced using two-color nanosecond laser excitation. We find that combined vis/UV excitation, for single-color pulse energies below the desorption threshold, induces neutral Mg-atom emission with hyperthermal kinetic energies in the range of 0.1-0.2 eV. The observed metal atom emission is consistent with a mechanism involving rapid electron transfer to three-coordinated Mg surface sites. The two-color Mg-atom signal is significant only for parallel laser polarizations and temporally overlapped laser pulses indicating that intermediate excited states are short-lived compared to the 5 ns laser pulse duration.     

Synchronous dual-wavelength operation of a self-injection-seeded narrow-linewidth flash-lamp-pumped Q-switched Ti:Al2O3 laser

Perfect synchronization of two different wavelength oscillations that are tunable within a range of 770-820nm is obtained from a self-injection-seeded Q-switched flash-lamp-pumped Ti:Al(2)O(3)laser. In spite of a significant time difference (as much as 2 mus) between the two seed pulses generated in the master oscillator, a common Pockels cell switch synchronizes the two injection-seeded Q-switched pulses growing from spatially separated slave oscillators in a common laser rod within a delay time of <3ns , depending on the combination of the two wavelengths. A sum output energy of ~41mJ/pulse was obtained for a pair of 780- and 810-nm pulses with a typical pulse width of ~30ns (FWHM).     

Efficient generation of third harmonic radiation in air filaments: A revisit

In this paper we revisit the third harmonic generation from a femtosecond laser filament in air and its significant enhancement (~ 100 times) with a intercepting pump pulse, which has been reported very recently. The enhanced third harmonic is studied as a function of the pulse polarization, time delay between the pump and signal pulses, laser pulse energy, etc. We provide an explanation for the enhancement of third harmonic based on a quenching of interference effects present near filamentation threshold. Simulations based on a two-color propagation code reproduce well the experimental observations and confirm our interpretation.     

Voltage-on-Type RTP Pockels Cell for <Emphasis Type="Italic">Q</Emphasis>-switch of an Er:YAG Laser at 1,617 nm

We report a resonantly diode-pumped electro-optic Q-switched Er:YAG laser operating at 1,617 nm using a voltage-on-type rubidium titanyl phosphate (RTP) Pockels cell as the modulator. The Er:YAG laser operates at a very stable Q-switching mode with a per pulse energy yield of 1.5 mJ and a pulse duration of 114 ns at 1 kHz PRF under an incident pump power of 21.6 W.     

Photonic generation of ultrawideband signals by exploiting gain saturation of dark pump pulse with double undershoots in a highly nonlinear fiber

We have proposed and theoretically demonstrated an alternative photonic scheme to generate ultrawideband (UWB) doublet pulses based on gain saturation effect in one piece of highly nonlinear fiber (HNLF). A flexible format swap between UWB doublet and monocycle pulses can be successfully realized by properly tuning the optical tunable delay line (ODL). Moreover, the key parameters for UWB pulse, including the center frequency (Fc), 10 dB bandwidth (BW_10dB), and fractional bandwidth (FBW), are also investigated with Fc being Einstein shift when the doublet pulse transforms into the monocycle pulse. Finally, our proposed scheme exhibits good performance that the obtained UWB pulse can have a FBW of > 100% at the Fc of ~ 7 GHz and UWB-over-fiber technology is also implemented without dispersion management.     

Slow and fast light based on SBS with the spectrum tailoring

In this paper, slow and fast light of a signal pulse of nanosecond duration are achieved in the same experimental device by using band-pass filters to tailor the spectra of spontaneous Brillouin scattering (SPBS) coming from 50 km single-mode optical fibers (SMF) as the pump light. The phase matching condition of slow and fast light is satisfied by changing wavelengths of band-pass filters .In our experiment, we obtain the tunable delay time for various signal pulses range from 1 ns to 20 ns. By increasing the power of the pump field to 16 mW, a 1 ns signal pulse is delayed 1.5 ns and is advanced 1.0 ns respectively, while the signal pulse almost has no distortion. The experiment has demonstrated that larger relative pulse delay of slow and fast light can be obtained in the same experimental setup when pump power is lower.     

AOM fourfold pass for efficient Q-switching and stable high peak power laser pulses

We report on a scheme for efficient acousto-optical Q-switching. A flash lamp pumped Nd:YAG oscillator with an acousto-optic modulator (AOM) fourfold pass configuration is presented. The setup combines two important advantages: enhancement of the diffraction efficiency by additional AOM passes and a compact oscillator design in spite of an extension of the optical path length. A flash lamp pumped oscillator with an average output power of 7 W and a beam quality of M² = 1.2 is developed. The system operates with a 100 Hz repetition rate for the flash lamps. In each pumping pulse a pulse train of 1 up to 40 Q-switched laser pulses is generated. The pulse duration is from 15 to 120 ns. In comparison to a former setup (AOM double pass) the AOM fourfold pass configuration allows single pulses with energy above 20 mJ and a pulse peak power of more than 1 MW. In addition, the beam profile is improved due to a better separation of the incident and diffracted beam caused by the AOM. The laser is dedicated as master oscillator in a master oscillator power amplifier (MOPA) system where pulse peak powers in the MW range should be achieved.     

Ultraviolet laser microstructuring of silicon and the effect of laser pulse duration on the surface morphology

The study of the laser pulse duration effect on the silicon micro-spikes morphology is presented. The microcones were produced by ultraviolet (248 nm) laser irradiation of doped Si wafers in SF₆ environment. The laser pulse duration was adjusted at 450 fs, 5 ps and 15 ns. We have analyzed the statistical nature of the spikes’ morphological characteristics, such as periodicity and apex angle by exploiting image processing techniques, on SEM images of the irradiated samples. The correlation of the quantitative morphological characteristics with the laser parameters (pulse duration, laser fluence and number of pulses) provides new insight on the physical mechanisms, which are involved on the formation of Si microcones.     

Specialty Yb fiber amplifier for microchip Nd laser: Towards ∼1-mJ/1-ns output at kHz-range repetition rate

We demonstrate and optimize, for a mJ/ns release at the wavelength 1.064 μm, the operation of a compact laser system designed in the form of a hybrid, active-passive, Q-switched Nd³⁺:YAG/Cr⁴⁺:YAG microchip laser seeding an Yb-doped specialty multi-port fiber amplifier. As the result of the amplifier optimization, ∼1 mJ, ∼1 ns, almost single-mode pulses at a 1-10-kHz repetition rate are achieved, given by a gain factor of ∼19 dB for an 11-μJ input from the microchip laser. Meanwhile, a lower pulse energy, ∼120 μJ, but a much higher gain (∼25 dB) are eligible for the less powerful (0.35 μJ) input pulses.     

Effect of pulse repetition rate and number of pulses in the analysis of polypropylene and high density polyethylene by nanosecond infrared laser induced breakdown spectroscopy

Pulse repetition rates and the number of laser pulses are among the most important parameters that do affect the analysis of solid materials by laser induced breakdown spectroscopy, and the knowledge of their effects is of fundamental importance for suggesting analytical strategies when dealing with laser ablation processes of polymers. In this contribution, the influence of these parameters in the ablated mass and in the features of craters was evaluated in polypropylene and high density polyethylene plates containing pigment-based PbCrO₄. Surface characterization and craters profile were carried out by perfilometry and scanning electron microscopy. Area, volume and profile of craters were obtained using Taylor Map software. A laser induced breakdown spectroscopy system consisted of a Q-Switched Nd:YAG laser (1064 nm, 5 ns) and an Echelle spectrometer equipped with ICCD detector were used. The evaluated operating conditions consisted of 10, 25 and 50 laser pulses at 1, 5 and 10 Hz, 250 mJ/pulse (85 J cm⁻²), 2 μs delay time and 6 μs integration time gate. Differences in the topographical features among craters of both polymers were observed. The decrease in the repetition rate resulted in irregular craters and formation of edges, especially in polypropylene sample. The differences in the topographical features and ablated masses were attributed to the influence of the degree of crystallinity, crystalline melting temperature and glass transition temperature in the ablation process of the high density polyethylene and polypropylene. It was also observed that the intensities of chromium and lead emission signals obtained at 10 Hz were two times higher than at 5 Hz by keeping the number of laser pulses constant.     

Generation of high average power 1 kHz shaped THz pulses via optical rectification

Generation of near single-cycle THz pulses from lithium niobate with 3.3 μJ energy, 3.3 mW average power, 1.2 THz central frequency and 4 MW peak power was demonstrated by tilting the intensity front of the pump pulses from a 1 kHz Ti:sapphire laser. THz pulse intensity as high as 200 MW/cm² was achieved. The energy conversion efficiency was 7 × 10⁻⁴. The capability of the present scheme to generate high energy shaped THz pulses was also demonstrated by using a sequence of optical pump pulses.