ADVERTISEMENT

Construction Of An Ultrafast Broadband Infrared Pump For Spectroscopy Measurements

Over the past few decades, time-resolved ultrafast spectroscopy measurements have emerged as new frontiers of condensed matter physics via manipulating and detecting different orders of quantum materials.

By combining some traditional experimental techniques with ultrafast pulse lasers, such as angle-resolved photoemission spectroscopy (ARPES), X-ray diffraction (XRD) and optical spectroscopy, ultrafast pump-probe experiments can provide new insights into the electronic nature of quantum materials. This is done by selectively exciting certain quasiparticles or different degree of freedoms with ”pump” pulses, and subsequently tracking their decay pathways back to the equilibrium state with the ”probe” beam, i.e. time-resolved ARPES/XRD/optical spectroscopy.

ADVERTISEMENT

For strongly correlated materials, whose electronic, spin and orbital degrees of freedom are usually coupled and acting on multiple energy scales, infrared optical spectroscopy is a traditional and powerful tool for exploring the electronic properties, e.g. band gaps, single particle and collective excitations. Using commercial ultrafast lasers, which are often designed to generate narrowband pulses in NIR range (∼800 nm, ∼1.5 eV), an ultrafast 800 nm optical pump- 800 nm optical probe spectroscopy system can be constructed.

However, the energy of NIR pulses is completely overwhelmed, for the low-energy excitations in strongly correlated materials, such as superconducting energy gap, Josephson plasma resonances, and specific lattice vibrations, always extend from gigahertz to mid-infrared (MIR) frequencies. So if one wants to selectively control the low-energy excitations in strongly correlated materials without deliver- ing excess energy to other excitation pathways, it is a must to find a way to lower the energy scale of pump pulses. Thanks to recent developments in nonlinear optics, ultrafast laser pulses ranging from MIR to terahertz (THz) frequencies can be generated using non-linear materials, such as ZnTe, GaSe, and LiNbO3 crystals.

Researchers at Peking University recently constructed a tunable ultrafast broadband optical (wavelengths of 0.4μm–15μm, ∼80meV–3eV ) pump, THz (∼0.25–2.5 THz, ∼1meV–10meV) probe spectroscopy system in reflection geometry, which can provide a powerful tool for manipulating and detecting different orders in strongly correlated materials.

A two-output optical parametric amplifier (OPA), pumped with an amplified Ti:sapphire laser system producing 800 nm, 35 fs pulses at a 1 kHz repetition rate, is used for pump pulse generation. The signal and idler beams of the OPA can be used as NIR pump pulses directly. To obtain the MIR pump pulses, two signal beams are used for difference frequency generation (DFG) collinearly on a 1-mm-thick z-cut GaSe crystal. By tuning the frequency of the two signal beams and the orientation of the GaSe crystal to meet the phase-matching conditions, MIR pulses with tunable polarization ranging from 3 to 15 μm can be generated. The THz probe pulses are generated by 800 nm pulses using a 1-mm-thick (110) ZnTe crystal and the THz profile was detected via electro-optic sampling. Samples sit at the end of a cold finger in a helium continuous-flow cryostat, which is capable of reaching a base pressure as low as 2×10−5 Pa and a temperature of 4 K.

ADVERTISEMENT

As an application of the ultrafast spectroscopy system, they performed near and mid-infrared pump, c-axis terahertz probe measurement on a superconducting single crystal La1.905Ba0.095CuO4 with Tc=32 K. A very sharp Josephson plasma edge develops near 18 cm−1 (∼0.54 THz) can be clearly seen in the reflectivity along c-axis below Tc, which indicates a Josephson plasma resonance mode. Using the tunable ultrafast broadband optical pump THz probe spectroscopy system, they observe the redshift of the original Josephson plasma edge and the emergence of a new light-induced edge at a higher energy within a very short time after excited by the strong NIR/MIR pulses (∼1.5 ps). The results imply that the light can induce new Josephson plasmon modes with different coupling strengths below Tc.

The construction of the ultrafast spectroscopy system is described in the article entitled Tunable near- to mid-infrared pump terahertz probe spectroscopy in reflection geometry, published in the journal Frontiers of Physics. This work was led by Nan-Lin Wang from Peking University.

Comments

READ THIS NEXT

CO2 Conversion: Turning Waste Into Value

The world needs more energy. As the population continues to grow and the quality of life improves in developing economies, […]

Attachment Moderates The Relationship Between Child Maltreatment And Dating Violence

Published by Carla Smith Stover, Associate Professor Yale University School of Medicine Child Study Center These findings are described in the […]

What Do Worms / Earthworms Eat?

Earthworms are tube-shaped segmented organisms that fall under the phylum Annelida. Contrary to popular perception, earthworms are not insects or arthropods—they are animals. Earthworms […]

When Policies Are Not Enough To Protect Us From Air Pollution, Pet Companions Might Be The Next Best Solution

Today, a growing number of countries are battling the rise in both air pollution and childhood hypertension. Often when air […]

An Improved Method To Remove Debris From Cyst Nematode Egg Suspensions And Computer-Aided Technologies For Egg Counting

Plant-parasitic nematodes infect the roots of plants, causing billions of dollars of crop loss worldwide. One such example is the […]

Deposition Definition In Science

Deposition, by definition in chemistry, refers to a phase transition in which matter transitions directly from a gaseous state into a […]

Food Safety: Green, Cost-Effective And Sensitive Method To Detect Metronidazole And Other 5-NDZ Residues In Food

In the current global food market, consumers are more concerned than ever about the food that they eat. Within this […]

Science Trends is a popular source of science news and education around the world. We cover everything from solar power cell technology to climate change to cancer research. We help hundreds of thousands of people every month learn about the world we live in and the latest scientific breakthroughs. Want to know more?