Generation, optimization, and application of ultrashort femtosecond pulse in mode-locked fiber lasers

A digital micromirror device (DMD) modulates laser intensity through computer control of the device. We experimentally investigate the performance of the modulation property of a DMD and optimize the modulation procedure through image correction. Furthermore, Laguerre-Gaussian (LG) beams with different topological charges are generated by projecting a series of forklike gratings onto the DMD. We measure the field distribution with and without correction, the energy of LG beams with different topological charges, and the polarization property in sequence. Experimental results demonstrate that it is possible to generate LG beams with a DMD that allows the use of a high-intensity laser with proper correction to the input images, and that the polarization state of the LG beam differs from that of the input beam.

Experimental generation of Laguerre-Gaussian beam using digital micromirror device

We have set up a novel system for shaping the Gaussian laser beams into super-Gaussian beams. The digital micro-mirror device (DMD) is able to modulate the laser light spatially through binary-amplitude modulation mechanism. With DMD, the irradiance of the laser beam can be redistributed flexibly and various beams with different intensity distribution can be produced. A super-Gaussian beam has been successfully shaped from the Gaussian beam with the use of DMD. This technique will be widely applied in lithography, quantum emulation and holographic optical tweezers which require precise control of beam profile.

Shaping super-Gaussian beam through digital micro-mirror device

A symmetric Airy beam (SAB) autofocuses during free space propagation. Such autofocusing SAB is useful in optical manipulation and biomedical imaging. However, its inherently limited autofocusing property may degrade the performance of the SAB in those applications. To enhance the autofocus, a symmetric apodization mask was proposed to regulate the SAB. In combination with the even cubic phase that shapes the SAB, this even exponential function mask with an adjustable parameter regulates the contribution of different frequency spectral components to the SAB. The propagation properties of this new amplitude modulated SAB (AMSAB) were investigated both theoretically and experimentally. Simulation shows that the energy distribution and autofocusing property of an AMSAB can be adjusted by the exponential amplitude modulation. Especially, the beam energy will be more concentrated in the central lobe once the even cubic phase is modulated by the mask with a higher proportion of high-frequency spectral components. Consequently, the autofocusing property and axial gradient force of AMSABs are efficiently enhanced. The experimental generation and characterization for AMSABs were implemented by modulating the collimated beam with a phase-only spatial light modulator. The experimental results well supported the theoretical predictions. With the ability to enhance the autofocus, the proposed exponential apodization modulation will make SAB more powerful in various applications, including optical trapping, fluorescence imaging and particle acceleration.

https://iopscience.iop.org/article/10.1088/2040-8978/18/7/075301/pdf

Dynamic enhancement of autofocusing property for symmetric Airy beam with exponential amplitude modulation

In this book, Applications of Monte Carlo Method in Science and Engineering, we further expose the broad range of applications of Monte Carlo simulation in the fields of Quantum Physics, Statistical Physics, Reliability, Medical Physics, Polycrystalline Materials, Ising Model, Chemistry, Agriculture, Food Processing, X-ray Imaging, Electron Dynamics in Doped Semiconductors, Metallurgy, Remote Sensing and much more diverse topics. The book chapters included in this volume clearly reflect the current scientific importance of Monte Carlo techniques in various fields of research.

/pdf/application-of-monte-carlo-simulation-in-optical-tweezers-1xj36qs1ps.pdf

Application of Monte Carlo Simulation in Optical Tweezers

Optical frequency comb (OFC) is a new type of high-quality laser source. The visible and near-infrared OFCs have become mature, and it has been widely used in optical frequency metrology, time/frequency transfer, precision laser spectroscopy and other fields. Since the mid and far-infrared spectral regions contain a large number of baseband absorption lines for molecules and the absorption intensities are several orders of magnitude higher than those in the visible and near-infrared spectral region, one has made great efforts to develop the mid and far-infrared OFCs in recent years. Although a variety of approaches to achieving infrared OFCs directly have been proposed, the method of difference frequency generation (DFG) infrared OFC based on the optical rectification technique is still more efficient. DFG infrared OFCs with widely tuning ability have been demonstrated based on fiber lasers so far. However, how to obtain the broadband spectrum for a DFG infrared OFC with widely tuning ability still needs to be solved. In this paper we report a fiber-type DFG infrared OFC by using the femtosecond pulses from a mode-locked erbium-doped fiber laser as the fundamental light. Based on the self-developed mode-locked fiber laser oscillator with repetition rate locked, the two-color fundamental pulse trains with the central wavelengths of 1.5 and 2.0 m are respectively achieved after the chirped pulse fiber amplification and all-fiber supercontinuum (SC) generation techniques have been utilized. With a time-domain synchronous detection system based on the intensity autocorrelation principle, the accurate synchronization with the fundamental two-color pulses is obtained by optimizing the OFS compensated fiber length and adjusting a tunable optical delay line. Finally, by using the optical rectification technique, a fiber-type DFG infrared OFC is successfully generated with the help of a suitable designed GaSe nonlinear crystal. Our experimental results also show that the spectral location of the DFG infrared OFC can be tuned by controlling the spectral shape of the SC combined with the adjustment of the phase-matching for the nonlinear crystal. The measured tuning range of the DFG infrared OFC is from 6 to 10 m, and the maximum spectral width is 1.3 m. This fiber-type DFG infrared OFC may play an important role in the molecular spectroscopy, the atmospheric environmental monitoring, and other fields.

Fiber-type difference frequency generation infrared optical frequency comb based on the femtosecond pulses generated by a mode-locked fiber laser

A phase plate was fabricated on a quartz crystal using ion beam etching technique with a predesigned angular phase mask, which can modulate the phase of light illuminating the phase plate by 0 and π rad. Analyzed the field distribution of the diffracted light by angular diffraction theory, which shows the resulting beam is a superposition of two Laguerre-Gaussian(LG) beams with opposite topological charges. Illuminating the phase plate using the expanded beam with diameter 4 mm generates the superposition of two LG beams with the same radian index p =0 and opposite angular index l =20 and l =-20 By increasing the aperture of the illuminating beam, LG beam with higher p index can be acquired, while the l index remains opposite.

Experimental generation of Laguerre-Gaussian beam using angular diffraction of binary phase plate

High-precision measurement of terahertz frequency using an unstabilized femtosecond laser

Aberrations in holographic array optical tweezers corrected with Zernike polynomials

Output pulse compressibility of the chirped pulse fiber amplification based on the dissipative solitons

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