We review the field of femtosecond pulse shaping, in which Fourier synthesis methods are used to generate nearly arbitrarily shaped ultrafast optical wave forms according to user specification. An emphasis is placed on programmable pulse shaping methods based on the use of spatial light modulators. After outlining the fundamental principles of pulse shaping, we then present a detailed discussion of pulse shaping using several different types of spatial light modulators. Finally, new research directions in pulse shaping, and applications of pulse shaping to optical communications, biomedical optical imaging, high power laser amplifiers, quantum control, and laser-electron beam interactions are reviewed.

Femtosecond pulse shaping using spatial light modulators

Exploring dynamics in the far-infrared with terahertz spectroscopy.

https://engineering.purdue.edu/~fsoptics/articles/Ultrafast_optical_pulse_shaping_tutorial-Weiner.pdf

Ultrafast optical pulse shaping: A tutorial review

The principles and most-recent results of high-power THz generation through optical rectification using a tilted optical pulse front are described. Single-cycle THz pulses of multimicrojoule energies are generated at kHz repetition rates, and average THz power levels exceeding 1 mW can be generated at kHz-MHz repetition rates. Applications in nonlinear THz spectroscopy and THz coherent control are discussed.

Generation of high-power terahertz pulses by tilted-pulse-front excitation and their application possibilities

Ultrabroad-bandwidth radiofrequency pulses offer significant applications potential, such as increased data transmission rate and multipath tolerance in wireless communications. Such ultrabroad-bandwidth pulses are inherently difficult to generate with chip-based electronics due to limits in digital-to-analog converter technology and high timing jitter. Photonic means of radiofrequency waveform generation, for example, by spectral shaping and frequency–time mapping, can overcome the bandwidth limit in electronic generation. However, previous bulk optic systems for radiofrequency arbitrary waveform generation do not offer the integration advantage of electronics. Here, we report a chip-scale, fully programmable spectral shaper consisting of cascaded multiple-channel microring resonators, on a silicon photonics platform that is compatible with electronic integrated circuit technology. Using such a spectral shaper, we demonstrate the generation of burst radiofrequency waveforms with programmable time-dependent amplitude, frequency and phase profiles, for frequencies up to 60 GHz. Our demonstration suggests potential for chip-scale photonic generation of ultrabroad-bandwidth arbitrary radiofrequency waveforms.

/pdf/ultrabroad-bandwidth-arbitrary-radiofrequency-waveform-3dl1kp5e7n.pdf

Ultrabroad-bandwidth arbitrary radiofrequency waveform generation with a silicon photonic chip-based spectral shaper

We describe the principles of free-space terahertz waveform synthesis by using a programmable optical pulse shaper to drive a photoconducting dipole antenna We illustrate this technique using several experimental examples, including manipulation of the amplitude and the phase of ultrafast terahertz waveforms as well as generation of ultrafast bit sequences at terahertz frequencies We present a theory which accurately predicts the shapes of the terahertz waveforms produced in our experiments In addition to the controllability of terahertz radiation, we have shown that optical pulse shaping can be used to avoid saturation of the terahertz field at high-peak power and increase generation efficiencies for terahertz radiations at selected, narrow-band frequencies

/pdf/terahertz-waveform-synthesis-via-optical-pulse-shaping-1y5autfl7y.pdf

Terahertz waveform synthesis via optical pulse shaping

We report the use of optical pulse shaping to convert single femtosecond pulses into lower-intensity pulse sequences for excitation of photoconductive dipole antennas, which results in the generation of bursts of tunable narrow-band free-space terahertz radiation. Our experiments demonstrate that the use of such pulse sequences can significantly enhance the spectral amplitude of the narrow-band terahertz radiation by avoiding the saturation effects that occur with single-pulse excitation. Our technique also provides the capability for terahertz wave-form shaping.

/pdf/enhancement-of-narrow-band-terahertz-radiation-from-4zc4rge7b2.pdf

Enhancement of narrow-band terahertz radiation from photoconducting antennas by optical pulse shaping.

Developing Ohmic contact systems or achieving low contact resistance is significant for high‐performance semiconductor devices. This work comprehensively investigates the interfacial properties of CrX2N4 (X = C, Si) based field‐effect transistors (FETs) with different metal (Ag, Au, Cu, Ni, Pd, Pt, Ti, and graphene) electrodes by using electronic structure calculations and quantum transport simulations. It is highlighted that the stronger interlayer coupling allows CrC2N4 to form an n‐type Ohmic contact with Ti electrode in the vertical direction. Furthermore, the absence of tunneling barrier at the CrC2N4–Ti interface greatly improves the electron injection efficiency. On the other hand, the studied metals form Schottky contact with CrC2N4 at the lateral interface due to Fermi level pinning (FLP) effects. Surprisingly, the strong FLP effects restrict the Schottky barrier heights of CrSi2N4‐metal contacts to a narrow range. Where Ag, Au, Ni, Pd, Pt, Ti electrodes and Ag, Ti electrodes form ideal ohmic contact with CrSi2N4 in the vertical and lateral directions, respectively, while the other metals form quasi‐ohmic contact. Ti exhibits the highest contact performance as the electrode in both CrC2N4 and CrSi2N4 based FETs. The findings may provide fundamental understanding for designing high‐performance and energy‐efficient FETs based on CrX2N4.

Efficient Ohmic Contact in Monolayer CrX2N4 (X = C, Si) Based Field‐Effect Transistors

Metal–Semiconductor Contacts In article number 2201056, Baisheng Sa and co-workers report the achievement of Ohmic and quasi-Ohmic contact in CrX2N4 (X = C, Si) contacts, which is due to Fermi level pinning effects. Thereby, channels are provided for electrons to pass through linked field-effect transistors easily. This system is analogous to high-speed trains going through mountain tunnels without climbing the peaks. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/aelm.202370013

Yongqian Liu

Papers

Terahertz waveform synthesis via optical pulse shaping

Enhancement of narrow-band terahertz radiation from photoconducting antennas by optical pulse shaping.

Efficient Ohmic Contact in Monolayer CrX2N4 (X = C, Si) Based Field‐Effect Transistors

Efficient Ohmic Contact in Monolayer CrX 2 N 4 (X = C, Si) Based Field‐Effect Transistors (Adv. Electron. Mater. 3/2023)