Li-Jin Chen

Bio: Li-Jin Chen is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Laser & Optical fiber. The author has an hindex of 19, co-authored 76 publications receiving 1530 citations. Previous affiliations of Li-Jin Chen include National Taiwan University.

High-energy pulse synthesis with sub-cycle waveform control for strong-field physics

Abstract: Over the last decade, control of atomic-scale electronic motion by non-perturbative optical fields has broken tremendous new ground with the advent of phase-controlled high-energy few-cycle pulse sources1. The development of close to single-cycle, carrier-envelope phase controlled, high-energy optical pulses has already led to isolated attosecond EUV pulse generation2, expanding ultrafast spectroscopy to attosecond resolution1. However, further investigation and control of these physical processes requires sub-cycle waveform shaping, which has not been achievable to date. Here, we present a light source, using coherent wavelength multiplexing, that enables sub-cycle waveform shaping with a two-octave-spanning spectrum and a pulse energy of 15 µJ. It offers full phase control and allows generation of any optical waveform supported by the amplified spectrum. Both energy and bandwidth scale linearly with the number of sub-modules, so the peak power scales quadratically. The demonstrated system is the prototype of a class of novel optical tools for attosecond control of strong-field physics experiments. Researchers present a waveform synthesis scheme that coherently multiplexes the outputs from two broadband optical parametric chirped-pulse amplifiers. The technique provides control at the sub-cycle scale and generates high-energy ultrashort waveforms for use in strong-field physics experiments.

Low-loss subwavelength plastic fiber for terahertz waveguiding.

Abstract: We report a simple subwavelength-diameter plastic wire, similar to an optical fiber, for guiding a terahertz wave with a low attenuation constant. With a large wavelength-to-fiber-core ratio, the fractional power delivered inside the lossy core is reduced, thus lowering the effective fiber attenuation constant. In our experiment we adopt a polyethylene fiber with a 200 µm diameter for guiding terahertz waves in the frequency range near 0.3 THz in which the attenuation constant is reduced to of the order of or less than 0.01 cm−1. Direct free-space coupling efficiency as high as 20% can be achieved by use of an off-axis parabolic mirror. Furthermore, all the plastic wires are readily available, with no need for complex or expensive fabrication.

Optical arbitrary waveform generation

Abstract: Advances in technology for optical arbitrary waveform generation will be described. Combs spanning two octaves, from 500nm to 2µm, based on GHz modelocked Ti:sapphire and erbium-fiber lasers, have been carrier-envelope stabilized and frequency referenced.

Highly efficient Cherenkov radiation in photonic crystal fibers for broadband visible wavelength generation

Abstract: We investigate the dependence of Cherenkov radiation (CR) on pump pulse parameters and its evolution along the propagation distance. Using a Ti:sapphire laser emitting 10fs pulses as the pump source, we demonstrate highly efficient (>40%), broadband (>50nm) CR in the visible-wavelength range with a threshold energy less than 100pJ and a tuning range over 100nm.

Calibration of an Astrophysical Spectrograph Below 1 m/s Using a Laser Frequency Comb

Abstract: We deployed two wavelength calibrators based on laser frequency combs (“astro-combs”) at an astronomical telescope. One astro-comb operated over a 100 nm band in the deep red (∼ 800 nm) and a second operated over a 20 nm band in the blue (∼ 400 nm). We used these red and blue astro-combs to calibrate a high-resolution astrophysical spectrograph integrated with a 1.5 m telescope, and demonstrated calibration precision and stability sufficient to enable detection of changes in stellar radial velocity < 1 m/s.

Imaging with terahertz radiation

Abstract: Within the last several years, the field of terahertz science and technology has changed dramatically. Many new advances in the technology for generation, manipulation, and detection of terahertz radiation have revolutionized the field. Much of this interest has been inspired by the promise of valuable new applications for terahertz imaging and sensing. Among a long list of proposed uses, one finds compelling needs such as security screening and quality control, as well as whimsical notions such as counting the almonds in a bar of chocolate. This list has grown in parallel with the development of new technologies and new paradigms for imaging and sensing. Many of these proposed applications exploit the unique capabilities of terahertz radiation to penetrate common packaging materials and provide spectroscopic information about the materials within. Several of the techniques used for terahertz imaging have been borrowed from other, more well established fields such as x-ray computed tomography and synthetic aperture radar. Others have been developed exclusively for the terahertz field, and have no analogies in other portions of the spectrum. This review provides a comprehensive description of the various techniques which have been employed for terahertz image formation, as well as discussing numerous examples which illustrate the many exciting potential uses for these emerging technologies.

Fiber-optic fluorescence imaging.

Abstract: Optical fibers guide light between separate locations and enable new types of fluorescence imaging. Fiber-optic fluorescence imaging systems include portable handheld microscopes, flexible endoscopes well suited for imaging within hollow tissue cavities and microendoscopes that allow minimally invasive high-resolution imaging deep within tissue. A challenge in the creation of such devices is the design and integration of miniaturized optical and mechanical components. Until recently, fiber-based fluorescence imaging was mainly limited to epifluorescence and scanning confocal modalities. Two new classes of photonic crystal fiber facilitate ultrashort pulse delivery for fiber-optic two-photon fluorescence imaging. An upcoming generation of fluorescence imaging devices will be based on microfabricated device components.

Roadmap on structured light

Abstract: Structured light refers to the generation and application of custom light fields. As the tools and technology to create and detect structured light have evolved, steadily the applications have begun to emerge. This roadmap touches on the key fields within structured light from the perspective of experts in those areas, providing insight into the current state and the challenges their respective fields face. Collectively the roadmap outlines the venerable nature of structured light research and the exciting prospects for the future that are yet to be realized.