Frequency Domain Spectroscopy

Major equipment in Dr. Padilla’s lab includes two Fourier Transform Infrared Spectrometers (FTIR) each equipped with an infrared microscope. This frequency domain spectrometer covers an extremely broad continuous frequency range from terahertz (300 GHz) to ultraviolet wavelengths (5eV). The spectrometer is housed in a vacuum compartment which permits precise characterization of transmission and reflection of samples at temperatures from 4.2K to 800K. The spectrometer also possesses the ability to perform time dependent measurements with time resolutions ranging from 2.5ns to several seconds.

Infrared Microscopy

The microscopes are a catoptric system and thus use only mirrors for reflection of light and image formation. As such it can operate over a large range of the electromagnetic spectrum from THz frequencies to optical wavelengths. A number of objectives with varying numerical aperture are available, thus providing diffraction limited imaging. By scanning the sample stage a total spatial area of 75mm x 50mm can be resolved.

A temperature controlled stage can be connected to our IR microscopes allowing for the characterization of samples at temperatures ranging from 77K to 693K. The stage has 8 electrical connections each of which can be connected to a probe.

Hyperion 2000 infrared  microscope:

o   Single pixel MCT detector – IR Measurements

o   Bolometer detectors – THz measurements

Hyperion 3000 infrared  microscope:

o   Single pixel MCT detector – IR Measurements

o   Bolometer detectors – THz measurements

o   Can perform spectral characterization of thermal emission from samples

Terahertz Spectroscopy

Another major piece of equipment in Dr. Padilla’s lab is a Hubner fiber coupled Terahertz time domain spectrometer (THz-TDS). This spectrometer is capable of determination of the optical constants of materials directly by characterizing the time dependence of the transmitted or reflected electric field. The instrument has a frequency coverage from 100 GHz to 2.5THz with a typical dynamic range greater than 1000:1, and consists of the following components; an femtosecond  fiber laser connected to terahertz emission and detection modules. The THz components of the system can be housed in a custom built vacuum box with an integrated vacuum cryostat to permit characterization of samples from 4.5K to 800K in both reflection and transmission modes.

Terahertz Imaging Systems

We have several custom built instruments for performing THz single pixel imaging. These systems are housed in a humidity controlled chamber to reduce signal attenuation cause by moisture in the air. Each imaging system consists of a THz source (typically a mercury arc lamp), imaging optics, a spatial light modulator, and a THz detector system (typically a bolometer connected to a lock in amplifier). The maximum image resolution we have obtained in our systems is 33x31.

Other THz equipment

 THz Source: Mercury Arc Lamps

THz Source: 580 GHz to 620 GHz Amplifier Multiplier Chain

o   1mW typical across band

o   2mW peak around 600GHz

4.2 K Bolometer System

o   NEP: ~1.2e-13

o   Frequency Response: up to 400 Hz

 Zero Bias Detector

o   NEP~ 5.1 pW/Hz^1/2

Optical Systems

Other optical systems used in the lab include:

Two digital mirror device developer kits including one with kHz refresh rates.

1 W tunable CO2 laser

Microwave Characterization

A pair of N5247A PNAX Agilent vector network analyzer (VNA) are also available within the Prof. Padilla’s laboratory. These VNAs provides a frequency span from 10 MHz to 67 GHz and have four ports (two of which can be configured as sources), enabling the complete characterization of not only the linear but also the nonlinear response of a sample. The N5247A is capable of measuring the amplitude and synchronous phase of all harmonics generated from a sample. An assortment of accessory items are available in Prof. Padilla’s lab for microwave experiments, including cables, waveguides, amplifiers, attenuators, phase-shifters, semi-rigid coaxial cables, horns and horn-lens assemblies, antennas and various adapters. The system has been upgraded with millimeter wave heads which extend the usable range to 110GHz.