Blog Post: Physics Career Day

Recently, the UCF Physics department put together their annual physics career day for central Florida high school students. The goal was to inform students what jobs, internships, and college experiences are available for students pursuing a physics major. The day started off with stories from professors and UCF physics graduates. Many of these graduates now work outside of the field of physics, such as improving artificial intelligence with Facebook or building space shuttles at NASA, and explained how a physics degree is very sought after by employers. This is because those with physics degrees have been trained in methods of learning, rather than just covering course material during college. Employers know this, and are very willing to hire employees that can not only think critically but also who learn more in a shorter training time.

As the morning continued into afternoon, the high school students had a chance to step inside and see a few actual operating physics laboratories. Among those was the Chini Ultrafast Lab, with John Beetar performing a demonstration with plasma.


Plasma is arguably the 4th state of matter (solid, liquid, gas, plasma). Essentially, when a gas is heated to extremely high temperatures, it is turned into a plasma. This occurs when thermal energy forces out an electron from a gas atom, leaving a positively charged ion and separate free electron. Due to these free electrons, plasma can carry an electric current, and is used everywhere from neon lights to televisions. In John’s experiment, he focused an infrared beam coming out of a laser on a specific point, giving the energy needed to rip electrons off air particles. This plasma is dangerous, as was shown when it burned a hole in a business card.

This demonstration not only showed high school students the real world application of physics and allowed them to see what experiments can consist of, but they also saw how physics is more than just bookwork; it is a very hands on field with a great future potential.

Blog Post: High Harmonic Generation


In the Chini ultrafast lab, we use ultrafast lasers that produce electromagnetic waves with a certain wavelength. To obtain these wavelengths, we take the ultrashort pulses generated by the laser and put them through a nonlinear process called high harmonic generation. Put simply, high harmonic generation passes electromagnetic pulses with an initial frequency through a material that creates new frequencies that are harmonics of the initial frequency (i.e.; three times, five times, ect.). This results in a new electromagnetic wave being outputted with a different wavelength than it had to begin. Unlike other harmonic generation mechanisms, high harmonic generation produces very high harmonics – typically in the 10’s to even 100’s of orders! This high harmonic generation can be obtained by using either a gas or a solid as the nonlinear material.

First, high harmonic generation can occur in various gases. On an atomic level, high harmonic generation occurs when an electromagnetic pulse penetrates a gas. The pulse interacts with a gas atom by removing an electron from its valence shell. Then, the electron is accelerated while outside the atom, causing it to gain kinetic energy from the electric field generated by the passing electromagnetic pulse [3]. After being accelerated, the electron is forced back into the parent atom, resulting in a deionization of the gas atom. However, due to conservation of energy, the kinetic energy gained by the electron through its acceleration needs to be released somehow, and this is where the new harmonic pulse comes from.

Image result for corkum, p. phys. rev. lett. 71, 1994 (1993). 3 step high harmonic generation

Fig. 1. Visual representation of high harmonic generation three step process in a gas. Quantum tunneling is shown on the far left, followed by electron acceleration from an electric field and recombination of electron and parent ion [1].

Alternatively, high harmonic generation can occur through a solid target through a slightly different process. In a solid, an electron hole pair must be generated. This means that an electron gains energy and jumps to a higher electron shell than the valence shell, leaving a hole in the valence shell and an electron in the conduction band (electron is excited above band gap) [2]. The electron and hole are then rapidly driven further apart by the laser pulse, causing a gain in kinetic and electric potential energy. Then, similar to high harmonic generation in a gas, the electron and hole are accelerated toward each other and combine. When this occurs, a harmonic photon with energy equal to the energy difference between the electron and hole is released, creating a new harmonic.

In the Chini lab, we are using high harmonic generation in solids as a tool to both learn more about the properties of different solid-state materials and develop new laser light sources. I’ll post in the future about what it’s like to work on high harmonic generation experiments, including some of the difficulties that come with researching the relatively new field of solid nonlinear materials.



  1. Corkum, P. Phys. Rev. Lett. 71, 1994 (1993).
  2. Marangos, J. “High Harmonic Generation Solid Progress” 7, 97-98 (2011).
  3. Hecht, J. “High harmonic generation pushes spectroscopy to the cutting edge,”

Student Takes Over Ultrafast News Blog


Hello everyone. My name is William Meldrum-Thush, and I am the new editor of the Chini Ultrafast Research Group news blog. I am currently a senior at Lyman High School taking 6 Advanced Placement courses. Outside of class, I participate in band and tennis as well as clubs such as National Honor Society and Modern Music Masters. My recent scholastic achievements include passing REC’s pre-engineering certification test and being nominated as a National Merit Scholar semifinalist. Some future blog posts include news from the lab, interviews with the graduate and undergraduate researchers, and short articles about the types of research we are conducting. I look forward to transforming this blog into both a learning tool as well as an outlet for updates on the research of the ultrafast lab!