Chirped Pulse Amplification Laser Research Articles

Experimental research and application of pulse clean technique based on cross polarized wave generation

Cross polarized wave (XPW) generation technique is used to improve the contrast of the output pulses from a 800 nm Ti: sapphire femtosecond (fs) laser. The measured temporal contrast of the cleaned pulse is 1011 (limited by the dynamic range of the third-order auto-correlator), which is 3 orders of magnitude higher than the temporal contrast ratio of the initial pulse. The efficiency of XPW is 22%. And the bandwidth of the cleaned pulse is broadened after the XPW nonlinear process. Through the dispersion compensation using double chirped mirrors and fused silica plate, the 25 fs pulse duration is achieved. With the cleaned pulse used as the seed of a TW-level Ti: sapphire chirped-pulse amplification laser system, the 250 mJ/50 fs pulses corresponding to 5 TW peak power are obtained. And the 1011 temporal contrast is demonstrated on the time scale of hundreds of picoseconds before the main femtosecond pulse.

Hundred mJ, sub-picoseconds, high temporal contrast OPCPA/Yb:YAG ceramic thin disk hybrid laser system

The authors have demonstrated an optical parametric chirped-pulse amplification (OPCPA)/Yb:YAG ceramic thin disk hybrid laser system having hundred mJ level pulse energy sub-picosecond pulse duration with high temporal contrast. At an input chirped-pulse energy of 3.8 mJ from an OPCPA preamplifier an output energy of 130 mJ has been generated from multipass diode-pumped Yb:YAG ceramic thin disk amplifier. A recompressed pulse duration of 450 fs with a contrast level of less than 7.2×10−9 at −150 ps before the main pulse has been obtained. The contrast level is the highest value achieved in Yb:YAG chirped-pulse amplification (CPA) laser system at 100 mJ level.

Carrier envelope phase stabilization of a Yb:KGW laser amplifier

In this paper we report on the active stabilization of the carrier envelope phase (CEP) of a Yb:KGW chirped pulse amplifier laser system seeded by a Yb-doped solid-state Kerr-lens mode-locked oscillator. The regenerative amplifier delivers 180 fs CEP stable pulses of 30 μJ-1 mJ energy at a repetition rate tunable from 1 to 200 kHz. The bandwidth of the feedback loop was extended by a factor of 5 using a specially designed high-pass filter, which resulted in a dramatic decrease of CEP jitter below 0.45 rad after the amplifier.

Prepulse suppression in a multi-10-TW diode-pumped Yb:glass laser

We describe a novel method to improve the temporal intensity contrast (TIC) between the main pulse and prepulses in a high-power chirped-pulse amplification (CPA) laser system. Pre- and post-pulses originating from the limited extinction ratio of the polarization gating equipment are suppressed by carefully adjusting the round-trip times of the regenerative amplifiers (RAs) with respect to the oscillator. As a result, leaking pulses from earlier or later round-trips in the RAs are hidden below the temporal shape of the main pulse. The synchronization can easily be controlled by a contrast measurement on a picosecond time scale using a third-order cross-correlator that enables a sub-mm precise adjustment of the cavity lengths. Finally, a method based on spectral interference is introduced that can be used for a fine-adjustment of the cavity lengths for the daily operation, making this new method easy to implement into existing laser systems.

Demonstration of a compact 100 Hz, 01 J, diode-pumped picosecond laser

We have demonstrated an all-diode-pumped Yb:YAG chirped pulse amplification laser that produces 100 mJ pulses of 5 ps duration at 100 Hz repetition rate. The compact laser system combines a room-temperature Yb:YAG regenerative amplifier for increased bandwidth and a cryogenically cooled Yb:YAG four-pass amplifier for improved heat dissipation and increased efficiency. The optical efficiency of this amplifier is higher than that of other diode-pumped systems of comparable energy.

High power all-fiber structured supercontinuum source with variable spectral coverage

An all-fiber structured supercontinuum source based on chirped pulse amplification (CPA) technology and the use of nonlinear photonic crystal fiber was constructed. By experimentally varying fiber stretcher length in CPA laser source, we can change the spectral coverage and therefore the percentage of visible light in the produced supercontinuum at output of nonlinear photonic crystal fiber, while the average supercontinuum power always keeps at watts of level. The all-fiber structured feature and the capability of changing supercontinuum spectral coverage make this CPA system a promising implement for different applications that require different broad band spectrum.

Efficient Spherical Wavefront Correction near the Focus for the 0.89 PW/29.0 fs Ti:Sapphire Laser Beam

We demonstrate a new loop system of the spherical wavefront (SW) correction near the beam focus to effectively improve the focusability of 0.89 PW/29.0 fs Ti:sapphire chirped pulse amplification laser. After wavefront correction, the Strehl ratio is improved to reach 0.91, and the focal spot size using the f/4 off-axis parabola is reduced to 6.34 × 6.94 μm2 (corresponding to 1.63 × 1.78 times diffraction limitation). With full peak power of 0.89 PW, the peak intensity of 2.59 × 1021 W/cm2 is obtained. The experimental results show that the SW correction scheme near the beam focus is comparatively simple, economic and high-efficient.

Compression grating alignment by far-field monitoring

Slight non-parallelism of the gratings in the compressor of a chirped-pulse amplification laser system produces angular chirp which results in a significant reduction of the focused intensity due to elongation of the pulse duration and enlargement of the focal spot. The effect of three-dimensional relative misalignment angles between two gratings on the far-field pattern of the pulses propagating through them is investigated by ray tracing. The far-field pattern provides two-dimensional information of the uncompensated angular dispersion directly. A simple and intuitive alignment procedure to achieve parallelism of the compression gratings by far-field monitoring is demonstrated experimentally, while the alignment precision is found to be the same as the methods proposed previously.

Contrast enhancement in a Ti:sapphire chirped-pulse amplification laser system with a noncollinear femtosecond optical-parametric amplifier

We experimentally demonstrated the contrast enhancement in a Ti:sapphire chirped-pulse amplification (CPA) laser with a noncollinear femtosecond optical-parametric amplifier. A total gain of 3.4 × 10(4) and pulse energy of 26 μJ were achieved. With the clean high-energy seeding pulse, the contrast ratio of the main amplified laser pulse to the amplified spontaneous emission in the Ti: sapphire CPA laser system was improved to around 10(10) within the time scale of hundreds of picoseconds.

Ultrafast temporal pulse shaping via phase-sensitive three-wave mixing

It is well-known that the process of optical parametric amplification (OPA) can be sensitive to the phases of the incident waves. In OPA realized by three-wave mixing, injection of all three waves into the same mode with appropriate phase relationship results in amplification of the signal phase, with an associated deamplification of the signal energy. Prospects for the use of this technique in the temporal domain for shaping ultrashort laser pulses are analyzed using a numerical model. Several representative pulse shaping capabilities of this technique are identified, which can significantly augment the performance of common passive pulse shaping methods operating in the Fourier domain. It is found that the use of phase-sensitive OPA shows a potential for significant compression of approximately 100 fs pulses, steepening of the rise time of ultrashort pulses, and production of pulse doublets and pulse trains. It is also shown that the group velocity mismatch can assist the shaping process. Such pulse shaping capabilities are found to be within reach of this technique in common nonlinear optical crystals pumped by pulses available from compact femtosecond chirped-pulse amplification laser systems.

2.4-Joule chirped pulse operation by a laser-diode-pumped slab laser for pumping non-collinear OPCPA

We present a diode-pumped chirped pulse amplification (CPA) system that generates multi-joule energy at a central wavelength of 1054 nm at a repetition rate of 10 Hz. The purpose of this laser is to serve as a pump source for non-collinear optical parametric chirped pulse amplification (NOPCPA). A Nd-doped glass slab with zigzag optical path was used as the gain medium of the main amplifier in this system to obtain multi-joule output with repeatable operation. The Nd:glass zigzag slab amplifier system consists of four-pass pre-amplification and four-pass power amplification. The seed pulse that is fed to the main amplifier was generated by a mode-locked fiber oscillator emitting at a 1053 nm central wavelength. The oscillator output was pulse-stretched to 2.7 ns duration with a 4.5 nm spectral bandwidth and amplified to 100 μJ by optical parametric amplification by use of type-I BBO crystals. After the main amplification, 2.4 J of energy in 3.7 nm of spectral bandwidth at 1 Hz repetition rate was obtained. This spectral bandwidth corresponds to a transform-limited pulse duration of 440 fs. This result indicates that our CPA laser is capable of delivering multi-joule pump light after pulse compression and frequency doubling for 30-TW NOPCPA system.

Short-wavelength soft-x-ray laser pumped in double-pulse single-beam non-normal incidence

We demonstrated a $7.36$ nm Ni-like samarium soft-x-ray laser, pumped by $36$ J of a neodymium:glass chirped-pulse amplification laser. Double-pulse single-beam non-normal-incidence pumping was applied for efficient soft-x-ray laser generation. In this case, the applied technique included a single-optic focusing geometry for large beam diameters, a single-pass grating compressor, traveling-wave tuning capability, and an optimized high-energy laser double pulse. This scheme has the potential for even shorter-wavelength soft-x-ray laser pumping.

High temporal and spatial quality petawatt-class Ti:sapphire chirped-pulse amplification laser system

Optical parametric chirped-pulse amplification (OPCPA) operation with low gain by seeding with high-energy, clean pulses is shown to significantly improve the contrast to better than 10(-10) to 10(-11) in a high-intensity Ti:sapphire laser system that is based on chirped-pulse amplification. In addition to the high-contrast broadband, high-energy output from the final amplifier is achieved with a flat-topped spatial profile of filling factor near 77%. This is the result of pump beam spatial profile homogenization with diffractive optical elements. Final pulse energies exceed 30 J, indicating capability for reaching peak powers in excess of 500 TW.

Amplified spontaneous emission contrast of CPA laser

The influence on the level of amplified spontaneous emission (ASE) contrast resulting from the different seed pulse energies has been experimentally studied in a 10-TW-level femtosecond Ti:sapphire chirped pulse amplification laser. It is found that, with the seed pulse energy increasing, the ASE pedestal is suppressed more efficiently, and the ASE contrast is improved with a saturable tendency. The measurement of ~2×10-8 ASE contrast in the range of more than 50 ps before the main pulse is achieved in the laser.

Enhancement of contrast ratio in chirped pulse amplified laser system by cross-polarized wave generation

This paper reports our experimental research on the laser contrast ratio enhancement in the XL-Ⅲ (eXtreme Light Ⅲ) facility with the technology of cross-polarized wave (XPW) generation. Based on the theoretical analysis of the relerant principles, we introduced an XPW filter in the facility, which was upgraded with a double chirped pulse amplification (DCPA) scheme. Under optimized system design and alignment, we measured the conversion efficiency from fundamental wave to cross-polarized wave to be higher than 10%. The pre-pulses in nanosecond scale were deeply suppressed and the contrast ratio in picosecond scale was enhanced from 10-5 to 10-7. Our results show the XPW generation provides an effective technique to improve the contrast ratio of a Chirped-pulse amplification laser system, which is a key issue in ultrahigh intensity laser-matter researches.

Demonstration of SubmicroJoule, Spatially Coherent Soft-X-ray Laser Pumped by 0.1 Hertz, 10 Joule, Picosecond Laser

We have demonstrated a spatially coherent 13.9 nm laser with submicroJoule output energy using a double-target geometry with a new driver system. The new driver was a chirped-pulse amplification laser with zigzag slab Nd:glass power amplifiers providing two beams with an energy of 10 J and picosecond duration at a shot rate of 0.1 Hz. The obtained 13.9 nm laser pulse with 1010 coherent photons will enable us to carry out single-shot pump-probe observation of nonperiodic ultrafast phenomena.

Carrier-envelope phase stabilization and control of 1 kHz, 6 mJ, 30 fs laser pulses from a Ti:sapphire regenerative amplifier

Carrier-envelope (CE) phase stabilization of a two-stage chirped pulse amplifier laser system with regenerative amplification as the preamplifier is demonstrated. The CE phase stability of this laser system is found to have a 90 mrad rms error averaged over 50 laser shots for a locking period of 4.5 h. The CE phase locking was confirmed unambiguously by experimental observation of the 2pi periodicity of the high-order harmonic spectrum generated by double optical gating.

Adaptive acousto-optic technique for femtosecond laser pulse shaping

We discuss the theoretical and experimental investigation of acousto-optic dispersive tunable filters, based on quasi-collinear geometry of light-sound interaction in a tellurium dioxide single crystal. The geometry uses the effect of strong acoustic anisotropy in the paratellurite as well as peculiarities of acoustic wave reflections at the free boundary of the crystal. A mathematical concept for determination of optical, electrical, and constructional parameters of the filters is developed. Different experimental acousto-optic filters intended for femtosecond pulse shaping are designed and tested. Preliminary experiments are performed in a subpetawatt optical parametric chirped pulse amplification laser system. The experimental data conform completely with the predicted data.

Evaluation of Femtosecond Laser-Induced Breakdown Spectroscopy for Analysis of Animal Tissues

The aim of this work was to evaluate the performance of femtosecond laser-induced breakdown spectroscopy (fs-LIBS) for the determination of elements in animal tissues. Sample pellets were prepared from certified reference materials, such as liver, kidney, muscle, hepatopancreas, and oyster, after cryogenic grinding assisted homogenization. Individual samples were placed in a two-axis computer-controlled translation stage that moved in the plane orthogonal to a beam originating from a Ti:Sapphire chirped-pulse amplification (CPA) laser system operating at 800 nm and producing a train of 840 microJ and 40 fs pulses at 90 Hz. The plasma emission was coupled into the optical fiber of a high-resolution intensified charge-coupled device (ICCD)-echelle spectrometer. Time-resolved characteristics of the laser-produced plasmas showed that the best results were obtained with delay times between 80 and 120 ns. Data obtained indicate both that it is a matrix-independent sampling process and that fs-LIBS can be used for the determination of Ca, Cu, Fe, K, Mg, Na, and P, but efforts must be made to obtain more appropriate detection limits for Al, Sr, and Zn.

The Nonlinear Ellipse Rotation in BK7 Glass Plate and its Application

The intensity-dependent nonlinear ellipse rotation of high-energy femtosecond pulse in BK7 glass plate is researched experimentally. The polarization, spectrum and shape of the femtosecond pulse were studied in this process. Based on this scheme, we develop a pulse temporal cleaner, which has been used in our femtosecond chirped pulse amplification (CPA) laser to provide a contrast ratio improvement of 2 orders of magnitude for the milli-joule level fs input pulses. The total transmission efficiency of the cleaner reaches 16.7%.