Self-referenced spectral interferometry is a widely used technique due to the advantages of spectral interference. However, the inherent nature of its self-referencing confines its measurements predominantly to pulses nearing the Fourier-transform limit. In this study, we introduce an improved self-referenced spectral interferometry method capable of characterizing large, chirped pulses. Based on this method, we successfully characterized a pulse with a duration of 87 fs, exceedingly twice the Fourier-transform-limited pulse width and obtained a temporal profile consistent with that measured using frequency-resolved optical gating.
To achieve multi-petawatt pulses, the generation of high-temporal-contrast few-cycle seed pulses with the central wavelength of 910 nm is the first step. In this research, high-performance seed pulses with a spectrum ranging from 800 nm to 1050 nm and pulse energy of 86 μJ are generated based on the filtered multi-plate spectral broadening and spectral filtering from a Yb-based femtosecond laser system. With self-phase modulation (SPM) induced spectral broadening, the input with relatively narrow spectrum bandwidth is broadened widely, which enables the final output pulse be compressed from full width at half maximum (FWHM) of 190 fs to 11.2 fs and a compression ratio of about 18 after dispersion compensation. The experiments show that the temporal contrast of the final output pulse is improved by at least four orders of magnitude through spectral filtering and new spectral components generated by third-order nonlinear processes such as SPM and self-focusing. Furthermore, taking advantage of single beam and self-focusing process, the final output has high energy stability and spectrum stability. Based on the merits above, together with its simplicity and robustness, this method proposed is expected to be used for the seed pulse generation of 10s-100s petawatt (PW) level laser system in the future.
Novel multicolor concentric annular ultrafast vector beams (MUCAU-VB) are generated simply by using cascaded four- wave mixing (CFWM) in a glass plate pumped by two intense vector femtosecond pulses. A proof-of-principle experiment shows that up to 10 frequency up-conversion concentric annular radially polarized sidebands are obtained simultaneously based on CFWM process, where the spectra range of the first 7 order sidebands extending from 545 nm to 725 nm. The results prove the polarization transfer property from the pump beam to the signal beams even in the CFWM, a third-order optical parametric process. The pulse duration of the first order sideband is measured to be 74 fs which is according with those of two input beams. Furthermore, the multicolor concentric annular ultrafast laser beams can be modulated externally using a controllable light modulator such as space light modulator. Due to the space separated property, color lights in different rings can be modulated to different polarized states respectively. Multicolor concentric ultrafast vector beams with uniform or nonuniform polarized structures can be generated. These novel MUCAU vector beams, which are manipulated in temporal, spectral, spatial domain and polarization state simultaneously, are expected to apply in wide fields, such as manipulating particles and multicolor pump-probe experiments.
In order to achieve global optimization in conventional optical imaging systems, complex optical design is required to eliminate various aberrations simultaneously. Imaging through scattering media can be achieved by the speckle autocorrelation method based on optical memory effect in a single-shot non-invasive way. By adding a scattering medium to the imaging system, multi-aberrations can be eliminated simultaneously. As an example, in a simple optical imaging system with spatially incoherent illumination, a ground glass plate is placed between the lens and the camera as a scattering medium. Finally, multi-aberrations such as spherical aberration, coma aberration and chromatic aberration are eliminated at the same time. Therefore, scattering media can be used as a tool to optimize optical imaging systems.
Light sheet fluorescence microscopy (LSFM) utilizes a light sheet to optically section samples, giving it the advantages of high signal-to-noise ratio, low phototoxicity and rapid three-dimensional imaging, which is an ideal tool for long-time microscopic observation of living samples. However, due to the inherent characteristics of Gaussian light sheet, there is a contradiction between the field of view and depth resolution of LSFM. In life science research, high depth resolution is necessary to resolve fine structures of biological systems such as neurons. However, in order to maintain a large field of view, the thickness of Gaussian light sheet is limited. Here, we propose a depth resolution enhancement method for LSFM. The incorporation of light field imaging into LSFM allows the acquirement of light field information within the Gaussian light sheet. By using the light field back projection (LFBP) reconstruction algorithm and depth estimation algorithm, it is possible to obtain the depth information in a light sheet, so as to improve the depth resolution. We built a light field light sheet fluorescence microscope (LFLSFM), and demonstrated it by fluorescent microsphere experiments. The proposed method can achieve a depth resolution of 0.5um when the thickness of the light sheet is kept at 6um to ensure a large field of view. Therefore, the method has potentialities in visualizing neural network of tissues and organs such as mouse brain.
High-energy PW laser pulses provide unprecedented extreme conditions which are key tools for exploring frontier fundamental researches. Recently, a new limitation from traditional grating-based pulse compressor appeared during achieve high-energy tens and hundreds PW laser pulses because the damage threshold and maximum size of diffraction gratings are not high or large enough to satisfy the requirement. Here, we propose feasible grating-based pulse compressors that can compress high-energy 100 PW laser pulse with a single beam. It contains two schemes, one is multistep pulse compressor that including pre-compressor, main compressor and post compressor, while the other is asymmetric four-grating compressor that replaces the pre-compressor and main compressor. The proposed novel grating-based pulse compressors increase the maximum bearable input and output pulse energies through modifying their spatiotemporal properties, and the introduced smoothing beam with spatial dispersion can be automatically compensated at the focal plane by using the spatiotemporal focusing technique. In this paper, we use Matlab to theoretically verify the possibility of the new grating-based pulse compressors. The simulation results are extremely consistent with our expectations that the two schemes can effectively smooth the beam by inducing spatial dispersion and effectively achieve 100 PW laser pulse. This creative optical design will simplify the high-energy compressor, improve the stability of PW laser system and ultimately increase the output laser energy, which allows us to explore more frontier fundamental researches.
Full characterization of few-cycle laser pulses is necessary for laser application. FROG is one of the most widely used full characterization techniques so far, and SRSI is another fresh one with attractive capacity. An all-reflective transient-grating based self-referenced spectral interferometry (AR-TG-SRSI) method is proposed for the single-shot characterization of few-cycle near Fourier transform-limited (FTL) laser pulses with a spectral range from UV to mid-IR. What’s more, a simple device FASI is built, which combines the FROG method and the SRSI method based on the same third-order TG effect in a single device. Pulses centered at 800 nm and 1800 nm were characterized by these two devices to verify their capacity. The two devices can characterize few-cycle pulses with a broad spectral range. And can characterize pulse by using the SRSI mode for well-compressed pulses. While, for complete pulses that own large chirp, the TG-FROG mode of the FASI device can also do the work.
Intense broadband optical-vortex pulses are expected to introduce new phenomena in nonlinear optical physics. We experimentally demonstrate the acquirement of about 500μJ, 220nm bandwidth (650nm – 870nm), and 16fs vortex ultrashort pulses by using a hollow fiber compressor. The Gaussian beam from a Ti:sapphire laser system at 800nm/50fs is transformed into vortex beam by using a spiral phase plate (SPP) firstly. Then, the narrowband optical vortex beam is spectrally broadened based on SPM in a 50-cm long hollow core fiber (HCF) filled with Ar at 0.5 bar, which is dispersion compensated using chirped mirrors. The total pulse energy transform efficiency is up to 56%. It is also found that orbital angular momentum (OAM) can be transferred to the newly generated spectral components by SPM effect..
An all-reflective transient-grating based self-referenced spectral interferometry (TG-SRSI) device is proposed. Except for a thin transparent Kerr medium used for self-referenced pulse generation, no transmitted material used in the device, which enables few-cycle pulses characterization with center wavelength from ultraviolet to near infrared. An 800 nm/8.1 fs and an 1800 nm/14.3fs pulse are characterized successfully using this device which proves its ability
Using 9 fs UV laser pulses, laser induced ultrafast dynamics in fused silica is investigated in the present study. The free
carrier dynamics under few-cycle UV laser excitation far below laser damage threshold in the fused silica was studied.
After laser excitation, free carrier in the conductive band is found to turn into self-trapped excitons within about 300fs. It
is possible that the trapped exciton will result in the incubation effect under the condition of ultrafast high-frequency
pulsed UV laser exposure.
A high-efficiency narrow-band 2000 nm Tm:YAG ceramic laser that combines the advantages of in-band pumping at 1617 nm and volume Bragg grating for wavelength selection was demonstrated. Using an output coupler with 10% transmission, a maximum output power of 1.64 W was obtained at 1999.9 nm under 4.56 W of incident pump power, corresponding to a slope efficiency of 50% with respect to the incident pump power. To the best of our knowledge, this is the highest slope efficiency achieved for 2000 nm Tm:YAG lasers so far.
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