Zhe Guang

Complete characterization of a spatiotemporally complex pulse by an improved single-frame pulse-measurement technique

We further develop a simple device, called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram (STRIPED FISH), for measuring the complete spatiotemporal intensity and phase, I(x,y,t) and ϕ(x,y,t), respectively, of an arbitrary ultrashort pulse on a single camera frame (and hence, on a single shot). We have increased the measurable bandwidth, eliminated most aberrations, and improved the uniformity of the multiple holograms in the device. We demonstrate these improvements by making single-camera-frame measurements of spatiotemporally complex subpicosecond crossed and chirped pulses from a Ti:sapphire oscillator. In order to display the massive resulting data files—pairs of four-dimensional intensity-and-phase data—we also develop a method for generating intuitive movies of the measured pulses. With these improvements, this device and its resulting movies should be able to perform and intuitively display true single-shot spatiotemporal measurements of most current ultrashort pulses.

Numerical simulations of holographic spatiospectral traces of spatiotemporally distorted ultrashort laser pulses.

We simulate traces for a catalog of spatiotemporally complex pulses measured using a single-shot complete spatiotemporal pulse-measurement technique we recently developed, called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram (STRIPED FISH). The only such technique ever developed to our knowledge, STRIPED FISH measures the complete spatiotemporal intensity I(x,y,t) and phase ϕ(x,y,t) of an arbitrary laser pulse using an experimentally recorded trace consisting of multiple digital holograms, one for each frequency present in the pulse. To understand the effects of various spatiotemporal distortions on the STRIPED FISH trace, we numerically investigate STRIPED FISH trace features for a catalog of pulses, including the spatially and temporally transform-limited pulse, temporal and spatial double pulses, spherically focusing and diverging pulses, self-phase modulated and self-focusing pulses, spatiotemporally coupled pulses, and pulses with complex structures. As a practical example, we also analyze an experimentally recorded trace of a focusing pulse with spatial chirp. Overall, we find that, from STRIPED FISHs informative trace, significant spatiotemporal characteristics of the unknown pulse can be immediately recognized from the camera frame. This, coupled with its simple pulse-retrieval algorithm, makes STRIPED FISH an excellent technique for measuring and monitoring ultrafast laser sources.

Measurement of the ultrafast lighthouse effect using a complete spatiotemporal pulse-characterization technique

Three of the four spatiotemporal pulse amplitude couplings—spatial chirp, angular dispersion, and pulse-front tilt—are well known for their important roles in optics and, especially, in ultrafast optics. The remaining one, only recently identified, corresponds to the pulse arrival time variation with angle and is known as the “ultrafast lighthouse effect.” This effect has important applications in attosecond science, but its characterization has not yet received much attention. In this work, we generate an ultrafast lighthouse and measure it using a recently developed single-frame complete spatiotemporal pulse-characterization technique called STRIPED FISH. We discuss in great detail the measured couplings in different domains and their roles in generating the ultrafast lighthouse effect. In addition, we display the propagation of the measured ultrafast lighthouse with an intuitive movie plot over space and time. We conclude that STRIPED FISH provides a simple and informative approach for measuring the ultrafast lighthouse effect and also other possible spatiotemporal distortions in the pulse, in both the horizontal and vertical dimensions.

Visualizing spatiotemporal pulse propagation: first-order spatiotemporal couplings in laser pulses

Even though a general theory of first-order spatiotemporal couplings exists in the literature, it is often difficult to visualize how these distortions affect laser pulses. In particular, it is difficult to show the spatiotemporal phase of pulses in a meaningful way. Here, we propose a general solution to plotting the electric fields of pulses in three-dimensional space that intuitively shows the effects of spatiotemporal phases. The temporal phase information is color-coded using spectrograms and color response functions, and the beam is propagated to show the spatial phase evolution. Using this plotting technique, we generate two- and three-dimensional images and movies that show the effects of spatiotemporal couplings.

Measuring spatiotemporal intensity-and-phase complexity of multimode fiber output pulses

We demonstrate ultrashort pulse spatiotemporal field measurement for multimode optical fibers, using a singleframe characterization technique, called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram (STRIPED FISH). We measure STRIPED FISH traces and retrieve the pulse field E(x,y,t) or equivalently E(x,y,ω), to generate movies revealing the field structure induced by propagating modes, due to their differences in field spatial distribution, modal propagation velocity and modal dispersion inside the fiber. We launch femtosecond pulses near 800nm from Ti: Sapphire laser to investigate linearly polarized modes LP01, LP11, LP02 and LP21 in multimode fibers.

Unstable multipulsing can be invisible to some ultrashort pulse measurement techniques

Simulations show that variable relative phase of a satellite pulse causes the satellite to wash out of a SPIDER measurement completely. FROG and autocorrelation measurements see satellite pulses but cannot determine their precise properties.

Real-time spatiotemporal measurement of ultrafast fields from multimode optical fibers

Ultrashort pulses emerging from multimode optical fibers are spatiotemporally complex—the multiple fiber modes have different spatial shapes and different propagation velocities and dispersions inside fibers. To measure the complete spatiotemporal field from multimode fibers in real time, we propose and demonstrate a technique for the complete measurement of these pulses using a simple pulse characterization technique, called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram (STRIPED FISH). It yields the complete electric field vs. space and time from multiple digital holograms, simultaneously recorded at different frequencies on a single camera frame.

Spatiotemporal coupling effects in ultrashort pulses and their visualization

The general theory of first-order spatiotemporal distortions provides a very helpful framework for understanding beam couplings in ultrashort pulses. The theory describes both real and imaginary coupling terms between 4 pairs of dimensions. The imaginary coupling terms are difficult to understand and visualize because they are difficult to plot in a meaningful way. In general, plotting the spatiotemporal intensity and phase of pulses in in two and three dimensions is a difficult problem. Our work on pulse visualization provides an unprecedented opportunity to study spatiotemporal couplings in ultrashort pulses. We create movies of pulses as they would appear naturally, with all of their evolving spatial, temporal, and spectral structure readily apparent.

Complete spatiotemporal measurement of ultrashort pulses emerging from multi-mode optical fiber

Using a newly developed technique, we measure the complete spatiotemporal field of ultrashort pulses emerging from dual-mode optical fibers, finding spatiotemporal complexity, introduced by the different spatial modes, having different group velocities and modal dispersions.

Simple single-shot complete spatiotemporal characterization of the intensity and phase of a complex ultrashort pulse

We demonstrate a simple single-shot device, called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram (STRIPED FISH), for completely characterizing the intensity and phase of an arbitrary ultrashort pulse in space and time (x,y,t). Improvements are made on the measurable bandwidth, aberrations eliminations, and the intensity uniformity of the multiple holograms in our device. To demonstrate the capability, we perform single-camera-frame measurements of spatiotemporally complex subpicosecond crossed and chirped double pulses from a Ti:Sapphire oscillator. To display the resulting four-dimensional intensity-and-phase data, we generate intuitive movies of the measured pulses based on our newly-developed method.