Pulse Stretcher Research Articles

A 110-TW multiple-beam laser system with a 5-TW wavelength-tunable auxiliary beam for versatile control of laser-plasma interaction

A Ti:sapphire laser system has been constructed with two synchronized main beams of 110 TW and 13 TW, and a 5-TW wavelength-tunable synchronized auxiliary beam for versatile control of laser-plasma interaction. The first main beam provides 3.3-J, 30-fs, 810-nm pulses, and the second 450-mJ, 34-fs, 805-nm pulses. The auxiliary beam comes from amplified spectral windows selected from a supercontinuum of high spatial coherence and provides 38-fs pulses with tunable wavelengths (870–920 nm). The two main beams can be focused down to M 2 = 1.2 and 1.1, with 77 and 81 % energy enclosed in the focal spots, respectively. The energy fluctuations are 1.1 and 1.8 %, and the pointing fluctuations are 4.5 and 4.8 μrad, respectively. By using a preamplifier and saturable absorber before the pulse stretcher to suppress amplified spontaneous emission, the temporal contrast of the 110-TW main beam reaches $$4 \times 10^{-10}$$ at the −100-ps timescale. Even though the auxiliary beam is generated from a highly nonlinear process, by confining the supercontinuum generation in a single self-trapping filament, a spatial coherence close to the main beams can be achieved. It can be focused down to M 2 = 1.3, with 72 % energy enclosed in the focal spot. The energy fluctuation is 2.6 %, and the pointing fluctuation is 4.7 μrad. The versatility of synchronized multiple-beams with tunable wavelengths, good energy and pointing stability, and the spatiotemporal quality of the laser system has been essential to our experiments in high-harmonic generation, extreme-UV lasers, and laser-wakefield accelerators in which precision control of laser-plasma interaction is facilitated by a concerted sequence of driving pulses.

Elimination of the chirp of narrowband terahertz pulses generated by chirped pulse beating using a tandem grating pair laser pulse stretcher.

We study the elimination of the chirp of narrowband terahertz pulses generated by chirped laser pulse beating using a laser pulse stretcher with two grating pairs that cancel out the third-order spectral phase. First, we show that positively chirped terahertz pulses can be generated using a pulse stretcher with a grating pair and internal lenses. We then combine this with a second grating pair, the spectral phase of which has the opposite sign to that of the first one. By varying the separation of the second grating pair, we experimentally verify that the chirp of the generated terahertz pulses can be eliminated.

Theoretical and experimental studies on a compact stretcher with large spectral bandwidth and high transmission efficiency

To ensure safe and effective amplification for the chirped pulse amplification laser facility, many factors such as pulse spectral width, pulse duration, grating parameters and incidence angle parameter are considered carefully in the design of the pulse stretcher. A compact four pass Offner stretcher design is given out. Experiment results show that the stretcher has broad spectral width, large stretching ratio and high transmission efficiency. By comparison, the calculated result of the dispersion effect on the pulse duration is completely consistent with the experiment result.

Fiber-based pulse stretcher for narrowband terahertz pulse generation with a chirped-pulse beating method

We theoretically show that it is possible to generate chirp-free terahertz (THz) pulses with a chirped-pulse beating method by using an optical fiber as a pulse stretcher. Proper choices of the core radius and the dopant fraction of the core material of a step-index single-mode optical fiber eliminate the third-order spectral phase of the fiber, thus giving the pump laser pulse a purely linear chirp. We also show that even a standard commercial single-mode optical fiber can give THz pulses of lower chirp than the lower limit for a grating pair. We perform experiments to verify our theory.

Phase noise suppression for a high-power optical frequency comb

We demonstrate a high-power frequency comb consisting of a Ti:sapphire bulk seed laser and a large-mode-area Yb-fiber power amplifier. An all-fiber pulse stretcher was carefully designed to suppress the amplitude-to-phase noise in the fiber amplifier. Near-Fourier-limited pulses were obtained with an average power of up to 30 W and a pulse duration of 178 fs. The free-running carrier–envelope-phase frequency was optimized to have a linewidth of 52 kHz, which was further phase-locked to a narrow linewidth of 1.8 mHz with an integrated phase noise of 0.78 rad.

An eye-safe, high-repetition rate single-mode femtosecond chirped pulse amplification system at 1560 nm

In this work we demonstrate a high-power, high-repetition rate chirped pulse amplification system operating at 1560 nm center wavelength. The system consists of a mode-locked Er-fiber oscillator, a grating-based pulse stretcher, a two-stage amplifier and a grating compressor. The system provides over 2.5 W of average output power with nearly transform limited, linearly polarized 390 fs pulses and 12.6 nJ pulse energy at 200 MHz repetition rate. The whole design is based on single-mode fibers, which allows excellent beam quality to be maintained.

Femtosecond fiber CPA system based on picosecond master oscillator and power amplifier with CCC fiber

Results of numerical and experimental investigations of the simple fiber CPA system seeded by nearly bandwidth-limited pulses from the picosecond oscillator are presented. We utilized self-phase modulation in a stretcher fiber to broaden the pulse spectrum and dispersion of the fiber to stretch pulses in time. During amplification in the ytterbium-doped CCC fiber, gain-shaping and self-phase modulation effects were observed, which improved pulse compression with a bulk diffraction grating compressor. After compression with spectral filtering, pulses with the duration of 400 fs and energy as high as 50 µJ were achieved, and the output beam quality was nearly diffraction-limited.

Chirped pulse amplification of a femtosecond Er-doped fiber laser mode-locked by a graphene saturable absorber

In this work we demonstrate for the first time, to our knowledge, a chirped pulse amplification (CPA) setup utilizing a graphene mode-locked femtosecond fiber laser as a seed source. The system consists of a mode-locked Er-fiber oscillator operating at 1560 nm wavelength, a grating-based pulse stretcher, two-stage amplifier and a grating compressor. The presented setup allows the amplification of the seed up to 1 W of average power (1000 times amplification) with linearly polarized 810 fs pulses and 20 nJ pulse energy at a 55 MHz repetition rate. The whole design is based on single-mode fibers, which allows one to maintain excellent beam quality, with M2 less than 1.17.

Amplification Characterization of Dissipative Soliton and Stretched Pulse Produced by Yb-Doped Fiber Laser Oscillator

Amplification Characterization of Dissipative Soliton and Stretched Pulse Produced by Yb-Doped Fiber Laser Oscillator

Effect of doped fiber length on the stretch pulses of a mode-locked erbium-doped fiber laser

A passively self-starting mode-locked fiber ring laser is demonstrated using a highly concentrated Erbium doped fiber (EDF) with a saturable absorber. The effect of EDF length on the performance of the laser is investigated. Stable stretched pulses are obtained at wavelength region of 1560nm with a repetition rate ranging from 10.1 to 12.1 MHz and a pulse width stretching from 0.52 to 0.75 ps as the EDF length is reduced from 4.5 to 1.5 m. The repetition rate goes higher as the cavity length decreases when a shorter EDF is used but the pulse width reduces as the EDF length increases since the total group velocity dispersion (GVD) in the cavity is close to zero. The article is published in the original.

Temporal contrast degradation at the focus of ultrafast pulses from high-frequency spectral phase modulation

The impact of high-frequency spectral phase modulation on the temporal contrast of ultrafast pulses is evaluated. Expressions are derived for the low-intensity pedestal produced by optical component surface roughness within pulse stretchers and compressors. Phase noise, added across the near-field of a spectrally dispersed beam, produces space–time coupling in the far-field or focal plane. The pedestal is swept across an area in the focal plane many times the size of the diffraction-limited spot. Simulations are performed for generic stretchers and compressors that show fundamentally different forms of temporal contrast degradation at focus.

Grism compressor for carrier-envelope phase-stable millijoule-energy chirped pulse amplifier lasers featuring bulk material stretcher

We demonstrate compression of amplified carrier-envelope phase (CEP)-stable laser pulses using paired transmission gratings and high-index prisms, or grisms, with chromatic dispersion matching that of a bulk material pulse stretcher. Grisms enable the use of larger bulk stretching factors and thereby higher energy pulses with lower B-integral in a compact amplifier design suitable for long-term CEP control.

Investigation of tunable stretcher for ultrashort pulses based on silica wires with subwavelength-diameters

A new type of tunable stretcher for ultra-short pulses is presented based on silica wires with subwavelength-diameters. Through proper design of the diameters of wires and the refractive indices of surrounding environment, we obtain large second-order dispersion and small higher-order dispersion, which are beneficial for pulses broadening around the operation wavelength. Analysis proves that 5-cm of such wires can broaden over 180 times for ultra-short pulses with 30-fs pulse-width. Tunable stretching ratio of stretcher is obtained by changing refractive indices of surrounding environment.

Sensor Data Transmission Overlay on Gigabit Passive Optical Networks

We propose and experimentally demonstrate overlaying an independent channel on a gigabit passive optical network (GPON). This has application to carry data collected from wireless sensor networks used for environmental monitoring on a public network. The overlaid channel, which utilizes highly stretched pulses to carry the low-rate sensor data, is unnoticeable in the presence of ordinary data channels. This overlaid channel can provide security for the sensor data because of its ultralow signal amplitude. Our experiment demonstrates that the GPON transmission experiences minimal performance degradation from the overlaid channel, indicating the feasibility of our approach. A cost-effective system architecture is proposed, and theoretical analysis shows the effect of the sensor data signal on the GPON data transmission performance.

Compact direct space-to-time pulse shaping with a phase-only spatial light modulator

A very compact and innovative pulse shaper is proposed and demonstrated. The standard architecture for pulse shaping that is composed of diffraction gratings associated with an amplitude-phase spatial light modulator (SLM) is replaced by a single phase-only SLM. It acts as a pulse stretcher and as an amplitude and phase modulator at the same time. Preliminary experiments demonstrate the accurate control of amplitude and phase of shaped pulses.

基于XeF(C-A)放大器的混合(固态/气态)超高功率飞秒激光系统

A terawatt hybrid laser(THL-100) system on the basis of a starting complex and a final amplifier with gaseous optically driven active media on XeF(C-A) molecules is presented.The starting complex manufactured consists of a Ti: sapphire master oscillator pumped by femtosecond pulses from a continuous laser pumped by(Verdy-8) at a wavelength of 532 nm,a femtosecond pulse stretcher,regenerative and multipass amplifiers pumped by a pulsed laser at a wavelength of 532 nm,a diffraction grating compressor and a second harmonic generator(KDP).The complex has the following output parameters of the laser beam: pulse duration is 50 fs,the energy of radiation at the second harmonic(475 nm) is 5 mJ.The complex can operate in a single pulse mode and a frequency of 10 Hz. The XeF(C-A) amplifier consists of a two high-voltage pulsed generator(linear transformer),a vacuum diode with six cold explosive-emission cathodes,a electron beam injection system,a Xe filled gas chamber-converter and a laser cell.The high-voltage generator consists of 12 transformer stages,and each of them involves eight capacitors(one is C=40 nF) and spark gaps.The capacitors can be charged up to voltage of 100 kV.E-beam in vacuum diode has the parameters in total current of 300 kA,peak voltage of 550 kV,pulse duration of e-beam power about 150 ns(FWHM).The total energies of the six 100 cm ×12 cm e-beams which pass through the foil into the Xe converter are 6-7 kJ in the 150-160 ns pulse(FWHM).Pump energy cascade processes lead rapidly to the formation of Xe*2,which radiates a fraction of the deposited energy in the continuum at(172 ± 5) nm.This VUV radiation is transmitted through CaF2 windows into the laser cell containing the mixture of XeF2 vapour and N2 buffer gas.VUV radiation makes photolysis of XeF2 molecules form XeF* excimer molecules.The active medium of the amplifier pumped by VUV radiation has 24 cm aperture and 110 cm length.The results of numerical modeling of the output parameters and first experimental results are presented in this paper.According to the modeling of the XeF(C-A) amplifier parameters and the first measurement of gain,it is shown that the maxmum output energy is 2-3 J,which means that the peak power has been up to 40-60 TW in a 50 fs pulse.Furthermore,It is very important that this laser system can provide a high temporal contrast up to 109-1010.

Generation of synchronized signal and pump pulses for an optical parametric chirped pulse amplification based multi-terawatt Nd:glass laser system

Synchronized signal (650 ps) and pump (1.3 ns) pulses were generated using 4-pass geometry in a grating pair based pulse stretcher unit. The pump pulse has been further amplified in a high gain regenerative amplifier. This amplified pulse was used as the pump in an optical parametric chirped pulse amplification based Nd:glass laser system. As the chirped signal pulse and the pump pulse originated from the same oscillator, the time jitter between the pump pulse and the signal pulse can be <50 ps.

Formation of metal nanoparticles of various sizes in plasma plumes produced by Ti:sapphire laser pulses

In this paper, an experimental study on generation of nanoparticle various sizes using Ti:sapphire laser pulses, is reported. Nanoparticle formation in plasma plumes of metals like silver and copper, expanding in vacuum, has been studied using stretched pulses of 300 ps duration [subnanoseconds (sub-ns)] from a Ti:sapphire laser. It has been compared with the nanoparticle formation (of the same materials) when compressed pulses of 45 fs duration were used under similar focusing conditions. Nanoparticle formation is observed at intensities as high as 2×1016 W/cm2. The structural analysis of the nanoparticle deposition on a silicon substrate showed that, using 45 fs pulses, smaller nanoparticles of average size ∼20 nm were generated, whereas on using the sub-ns pulses, larger particles were produced. Also, the visible light transmission and reflection from the nanoparticle film of Ag on glass substrate showed surface plasmon resonance (SPR). The SPR curves of the films of nanoparticles deposited by femtosecond pulses were always broader and reflection/transmission was always smaller when compared with the films formed using the sub-ns pulses, indicating smaller size particle formation by ultrashort pulses. Thus, it has been demonstrated that variation in the laser pulse duration of laser offers a simple tool for varying the size of the nanoparticles generated in plasma plumes.

Chirped-pulse amplification with narrowband pulses

We demonstrate a compact hyperdispersion stretcher and compressor pair that permit chirped-pulse amplification in Nd:YAG. We generate 750 mJ, 0.2 nm FWHM, 10 Hz pulses recompressed to an 8 ps near-transform-limited duration. The dispersion-matched pulse compressor and stretcher impart a chirp of 7300 ps/nm, in a 3 m x 1 m footprint.

Distortionless large-ratio stretcher for ultra-short pulses using photonic crystal fiber

A large-ratio stretcher for ultra-short pulses is proposed based on photonic crystal fiber (PCF). Through proper design of the PCF structure, we obtain over 300-nm wavelength range with flattened dispersion characteristics. Analysis indicates that 1-km of such fiber can broaden over 10,000 times for ultra-short pulses with <100-fs pulse-width. Distortion due to dispersion and nonlinearity is negligible.