Few-cycle 1.9-μm pulse generation via collinear spectrum synthesis in multiple-crystal OPA

Light-field synthesizer based on multidimensional solitary states in hollow-core fibers

Few-cycle, long-wavelength sources for generating isolated attosecond soft x ray pulses typically rely upon complex laser architectures. Here, we demonstrate a comparatively simple setup for generating sub-two-cycle pulses in the short-wave infrared based on multidimensional solitary states in an N₂O-filled hollow-core fiber and a two-channel light-field synthesizer. Due to the temporal phase imprinted by the rotational nonlinearity of the molecular gas, the redshifted (from 1.03 to 1.36 µm central wavelength) supercontinuum pulses generated from a Yb-doped laser amplifier are compressed from 280 to 7 fs using only bulk materials for dispersion compensation.

Efficient Generation of Spectrum-Manipulated Few-Cycle Laser Pulses through Cascaded Dual-Chirped OPA

The cascaded dual-chirped optical parametric amplification (DC-OPA) is presented for efficient generation of few-cycle infrared (IR) laser pulses. The input pulses are strategically chirped to optimize the phase-matching bandwidth in each nonlinear crystal, and four regions of the signal spectrum are amplified in cascaded crystals with different cutting angles, enabling flexible manipulation of the output spectrum. Broadband gain and high conversion efficiency are simultaneously achieved owing to the cascaded-crystal arrangement, the signal pulse duration of 4.2 cycles is obtained with 11.7-mJ pulse energy, corresponding to a conversion efficiency of 39.0%. The proposed scheme offers a robust and simple approach to pushing the phase-matching bandwidth limits introduced by the nonlinear crystal, which manifests great prospect in various researches involving ultrafast optics and strong-field physics.

Broadband mid-infrared coherent light source from fiber-laser-pumped difference frequency generators based on cascaded crystals

We present difference frequency generators (DFGs) using cascaded PPLN crystals, each with a distinct poling-period, as the parametric gain medium. We show that the phase-matching bandwidth of cascaded crystals is the combination of that of each individual crystal. In the non-phase-matched section of cascaded crystals, there exists periodic backward and forward frequency-conversion processes. Nonetheless, we demonstrate that such a periodic back-conversion process would not compromise the parametric gain bandwidth of cascaded nonlinear crystals. By using two PPLN crystals with poling periods of 31 µm and 29 µm, we experimentally obtained mid-infrared light sources having instantaneous-bandwidth covering 2.8-3.9 µm, which was roughly twice as much as that from a system based on a single crystal. Moreover, our numerical results show that light sources with an instantaneous-bandwidth covering 2.5-5 µm could be obtained by cascading more crystals. This scheme represents a promising technical route to transform conventional DFGs into a device capable of generating spatially-coherent light emission with very broad instantaneous-bandwidth.

Broad-bandwidth high-temporal-contrast carrier-envelope-phase-stabilized laser seed for 100 PW lasers

We demonstrate in this Letter the generation of carrier-envelope-phase (CEP)-stabilized laser pulses at 910 nm with simultaneously high-temporal-contrast, broad spectral bandwidths and few-cycle pulse durations. Through combining the techniques of cascaded optical parametric amplification (OPA) and second-harmonic generation (SHG) in the laser setup, a pulse temporal contrast as high as ${ \gt }{{10}^{12}}$>10¹² has been obtained at the laser output. During the OPA and SHG processes, both the pulse chirp and gain bandwidth are perfectly optimized, leading to the generation of 170 µJ pulses with ${ \gt }{200}\;{\rm nm}$>200nm bandwidth and ${\sim}{15}\;{\rm fs}$∼15fs pulse duration. Moreover, the CEP of the laser is stabilized passively to a noise level of less than 340 mrad. This high-quality pulsed light source, as the seed laser of the deuterated potassium dihydrogen phosphate (DKDP)-based 100 PW system, will be integrated into the Station of Extreme Light facility in the near future.

All-optical measurement of high-order fractional molecular echoes by high-order harmonic generation

An all-optical measurement of high-order fractional molecular echoes is demonstrated by using high-order harmonic generation (HHG). Excited by a pair of time-delayed short laser pulses, the signatures of full and high order fractional (1/2 and 1/3) alignment echoes are observed in the HHG signals measured from CO ₂ molecules at various time delays of the probe pulse. By increasing the time delay of the pump pulses, much higher order fractional (1/4) alignment echo is also observed in N ₂O molecules. With an analytic model based on the impulsive approximation, the spatiotemporal dynamics of the echo process are retrieved from the experiment. Compared to the typical molecular alignment revivals, high-order fractional molecular echoes are demonstrated to dephase more rapidly, which will open a new route towards the ultrashort-time measurement. The proposed HHG method paves an efficient way for accessing the high-order fractional echoes in molecules.

High-power and high-efficiency short wavelength operation of a Tm:YLF laser at 1.83 μm

A high-power and high-efficiency diode-end-pumped Tm:YLF laser at 1.83 μm is demonstrated for the first time, to our best knowledge. To make the laser operate at 1.83 μm, a simple way of controlling the transmittance of the output coupler is used, and the criteria of the transmittance of the output coupler at the emission peaks of Tm:YLF are theoretically analyzed, which are verified by experimental results. Based on the theoretical analysis, laser oscillation at only 1.83 μm is realized. Maximum output power at 1833 nm is 8.5 W with corresponding slope efficiency of 53.4% regarding absorbed pump power. In addition, tunability of this laser from 1827 nm to 1837 nm is obtained. Laser beam quality at 1833 nm is measured to be 1.4 at maximum output power. The achieved laser performance represents considerable improvement compared to any other bulk laser emitting around 1.83 μm.