> Kik Group College of Optics and Photonics UCF
The control electronics for the Near-field Scanning Optical Microscope
          



Laboratory

The study of nanophotonic structures requires an array of dedicated equipment, including various light sources, detectors, electronics, nanopositioning equipment, software, and more. This section gives an overview of some of the tools currently available in our NanoPhotonics Characterization Lab.

Students in the group actively fabricate nanophotonic structures using CREOL's own NanoPhotonics Fabrication Facility. For an impression of the tools that the group uses, have a look at the cleanroom photo gallery.


Witec Near-field Scanning Optical Microscope

A core component of the NanoPhotonics Characterization lab is the Witec AlphaSNOM, a combined Near-field Scanning Optical Microscope (NSOM), Atomic Force Microscope (AFM), and Confocal Microscope. All three techniques are indispensable in the investigation of nanophotonic structures.

- The AFM mode allows us to map out the topography of a sample with nanometer resolution, enabling the visualization of the structures that make up a nanophotonic integrated circuit.
- NSOM scans can be performed during AFM scanning, providing information about the optical properties (emission, absorption) of a sample with sub-diffraction limit resolution (typically 50-100 nm). The near-field optical probes also allow us to excite samples in a <100 nm spot, which is necessary for example for the local excitation of surface plasmons.
- Confocal microscopy can be used to collect light from a diffraction limited three-dimensional volume while rejecting light emitted or scattered outside that volume. This is an indispensable way to reduce any background light intensity in our experiments.

For more details on the quite extraordinary specifications of this piece of equipment, please visit the manufacturers product page.



Woollam M2000 Spectroscopic Ellipsometer

The M2000 High-Speed Scanning Variable Angle Spectroscopic Ellipsometer is a thin film and multilayer analysis tool that enables the rapid determination of linear optical properties (refractive index, absorption coefficient, depolarization factors, anisotropy) in a wide wavelength range spanning the UV, VIS, and NIR. The system, manufactured by J. A. Woollam is equipped with custom focusing optics that enable a measurement spot size as small as 100x100 um2. Array based detectors enable data collection across the full spectral range in under 5 seconds. The system features automated mapping, useful for example for the detection of film thickness gradients, semiconductor bandgap variation across a deposited layer, thickness homogeneity of a planar waveguide, etc. For more information, see the M2000 system specifications and a list of sample requirements.




Light sources

Ando AQ4321D Tunable Diode Laser

To analyze photonic circuits that operate at telecom compatible frequencies, we measure waveguide properties such as optical gain, transmission bandwidth, and waveguide loss. For this purpose we use the Ando AQ4321D Tunable Diode Laser. The emission wavelength can be tuned from 1520nm to 1620nm with an accuracy of 0.01nm and output powers of several milliwatts over the entire tuning range.



Spectra Physics 2060RS Krypton laser

Our research on light propagation on metal surfaces requires the ability to generate optical signals at many different frequencies. Krypton gas lasers can generate colors ranging from the ultraviolet (~350nm) to the red (~800nm). The broad spread in available laser lines from the Spectra Physics 2060RS laser allows us to study the propagation of surface plasmons (light trapped at metal surfaces) in a set of very different conditions. Laser output powers range from a few milliwatts to over a watt in the red.



1W green DPSS laser

The investigation of nanocrystal sensitized gain media requires a high power continuous wave laser. For this purpose we use the MGL-532-H, a 1W diode pumped solid state laser operating at 532nm manufactured by CNI Laser. This compact laser source offers four times the green output power of our 2060 Kr laser at ~1/20 of the price, 1/75 of the volume, and without the requirement of water cooling.



Jobin-Yvon Tunable White Light Source

Our Jobin-Yvon illumination system provides us with a tunable light source that operates in the wavelength range ~250nm - 2000nm, with typical powers in excess of range 1 mW/nm. The system consists of a 450W Xe lamp combined with a microHR monochromator. The instrument allows us to perform excitation spectroscopy on nanostructured gain media, to perform prism coupling measurements in a wide wavelength range, and to measure metal nanoparticle plasmon resonances by obtaining dark-field white light scattering spectra.





Near infrared pump lasers

Our work on optical nanocrystal sensitized optical gain media requires the ability to excite materials in various ways. One way is to illuminate the materials with light that can be absorbed by optical dopants in the material. For this purpose our lab houses high power diode pump lasers operating at 975nm and 1480nm. By focusing the output from these pump lasers onto our samples we can reach light intensities up to several megawatts per square cm. Our ILX LDC3900 controller (see image above) can drive and cool four of such diodes simultaneously.



Detectors

Ophir-Spiricon near-infrared camera

The Ophir-Spiricon phosphor-coated near-infrared camera SP1550M allows us to image waveguide mode profiles at telecom wavelengths. The camera houses a 640x480-pixel visible CCD array, coated with a phosphor layer that produces upconversion luminescence in response to incident near infrared light (sensitivity 1440-1605nm). Using dedicated laser beam profiling software, the resulting visible intensity distribution on the CCD is converted to the corresponding near-infrared intensity profile for quantitative mode analysis. The camera provides frame rates of 30Hz and shutter times as low as 10us, allowing for visualization of relatively high intensity beams without saturation effects.



The Applied Detector germanium detector

The Applied Detector Corp. Liquid Nitrogen cooled Ge detector is among the most sensitive near-infrared detectors available. The ADC Ge detector (previously known as the North Coast Ge detector) can detect light with wavelengths between 500-1750nm and features extremely low electronic noise. This allows us to detect light levels as low as 1 picowatt (one trillionth of a Watt), enabling us to investigate for example photoluminescence from erbium doped silicon nanocrystals. The image shows such Ge detector mounted on a Gatan cathodoluminescence system. In our lab it is currently connected to our monochromator



Andor TE cooled CCD camera

To detect the emission spectrum of nanophotonic materials at visible and NIR wavelengths (400nm-1000nm) we use an Andor DU-401 CCD camera. This type of detector uses an array of pixels to detect light. Combined with our monochromator which can divert light of different wavelengths onto different pixels, this allows us to simultaneously collect photons in a broad wavelength range, enabling to measure an entire photoluminescence spectrum in 4 ms. The CCD chip is cooled thermoelectrically to a temperature below -80 oC, dramatically reducing the electrical noise while maintaining an efficiency close to 100%.



Hamamatsu R4330 photomultiplier tube

When analyzing optically active materials, a lot of information can be derived from measuring time dependent signal intensity. Examples of materials properties that can be derived are absorption cross-section, emission cross-section, radiative and non-radiative decay rates, quantum efficiency, upconversion strength, and more. This type of measurement requires a fast optical detector. For this purpose we use the R-4330 photomultiplier tube (PMT). With this type of instrument we can detect single photons in the wavelength range 160-1040nm with a time resolution of 3ns. Thanks to the added thermoelectric cooler (see image above) this detector has an extremely low intrinsic noise: ~10 dark counts per second, equivalent to a few attowatt. Time resolved measurements are recorded using the PMT in combination with our monochromator and our multichannel scaler.



Hamamatsu R5509 NIR photomultiplier tube

In addition to the R4330 photomultiplier tube, we have recently acquired the R5509. This PMT has similar characteristics as the R4330 enabling single photon detection with a time resolution of  ~5ns, but it extends the sensitivity range into the near-infrared up to a maximum wavelength of ~1650nm.



Ando AQ6315E optical spectrum analyzer


The AQ-6315E optical spectrum analyzer (OSA) is an improved version of the well known Ando 6315A. This OSA can do spectrally resolved intensity measurements in the range 350-1750nm with a wavelength accuracy better than 0.05 nm. The system is sensitive enough to measure light intensities as low as a few picowatts, and in a single measurement can cover a dynamic range of seven (!) orders of magnitude, allowing for the simultaneous viewing of low intensity and high intensity signals such as spontaneous emission and laser emission from a laser cavity. It has several integrated measurement modes, from simple optical absorption measurements to full optical amplifier parameter analysis.



Newport 2832-C dual-channel optical power meter

The Newport 2832-C with the included 818-UV, 818-IR, and 818-IS-1 detector units can simultaneously measure the absolute power in two laser beams at wavelengths from 190nm-1700nm. In the lab it takes the role of a versatile 'optical multimeter' allowing for a quick measurement of the laser power during output optimization or as a pump-power monitor in photoluminescence and gain measurements.



Ocean Optics HR4000 USB spectrometer

The Ocean Optics HR4000 spectrometer is a compact grating spectrometer that we use to measure transmission and reflection spectra. Light is sent to the spectrometer via a multimode fiber, dispersed inside the spectrometer using a fixed grating, and directed toward a 3648 element CCD array. In this way different wavelengths are detected on different pixels of the CCD-array. The system offers fast detection (all wavelengths can be read out at once) and high resolution (the small pixel size of the CCD array implies that each pixel detects only a narrow wavelength range). For more information, see the HR4000 product page.





Electronics

SR810 digital lock-in amplifier


SR830

Much of our research deals with the detection of very weak light. To detect such low-level optical signals, we use sensitive detectors that produce an electrical output representing the light intensity. For extremely weak signals - which are unfortunately quite common - these electrical signals contain a lot of noise that is not related to the light source, but for example due to the light in the room, electrical interference, or thermal noise. Lock-in detection is an advanced technique in which the weak light source is intentionally modulated ('turned on and off') at a regular rate. A lock-in amplifier can be used to selectively pick up signals that are varying at this specific frequency, thus removing all uncorrelated and random electrical signals that were also present. Our Stanford Research Systems SR810 lock-in amplifier can be controlled and read out via GPIB, allowing for control via LabVIEW.



SR430 multichannel scaler


SR430

The SR430 multichannel scaler is used to characterize the output from our photomultiplier tube (PMT). The PMT produces a series of extremely short electrical pulses (a few nanoseconds long), each of which represents a detected photon. The SR430 recognizes and counts these pulses, and can display them as a function of time. Using its dedicated electronics it can count up to 250 million individual photons per second with a time resolution of 5ns, allowing us for example to rapidly and accurately measure photoluminescence lifetimes.





Nanopositioning equipment

Melles Griot / Thorlabs NanoMax

NanoMax

Launching light from an optical fiber into nanophotonic waveguides requires extremely precise alignment of the excitation light source and the waveguide. For this purpose we use the NanoMax, a piezo-controlled three-axis alignment stage with a fine stage travel of 20x20x20um. Integrated position readout and an active feedback loop allows for stable positioning with an accuracy of 5 nanometer. The NanoMax is currently sold by Thorlabs



Melles Griot Nanomover system

Nanomover

For micropositioning we make use of the Nanomover system. By replacing manual micrometers with these stepper motor controlled actuators, positioning accuracy better than 100nm can be achieved over distances up to 25mm, with speeds up to 2.5mm per second. The actuators and controllers present in our laboratory were donated by Melles Griot, who is one of the College's Industrial Affiliates.



PI NanoCube

PI Nanocube piezo system

For accurate positioning of optics in confined spaces, we use the Physik Instrumente NanoCube. This stage is only 50x50x44mm in size, and allows for piezo-controlled three-axis alignment with a total of 100x100x100um. Active feedback results in a position accuracy of 2 nm.





Software

Microwave Studio (MWS) simulation suite

Magnitude of the electric field around a 50 nm diameter Au particle on SiO2 during illumination with green light.

To model the behavior of complex nanostructured materials we use Microwave Studio (MWS), a 3D simulation code based on the Finite Integration Technique, which is related to the well known Finite Difference Time Domain method. Both methods numerically solve discretized versions of Maxwell's equations. For our work on metallic nanostructures a realistic description of the optical response of metals is essential. Microwave Studio includes Drude, Debye, and Lorentz descriptions of the dielectric function, allowing us to accurately simulate the frequency dependent response of a wide variety of materials.





Other equipment

ARS extended range optical cryostat

ARS cryostat

The ARS variable temperature closed cycle optical cryostat enables us to study the optical properties of materials over a wide temperature range, from 10K up to 800K. The ability to cover such a wide temperature range in a single system without breaking vacuum is an unusual capability, allowing us to study processes such as energy backtransfer in rare earth doped semiconductor materials. Dedicated gas inlets on the cryostat further allow us to perform in-situ measurements of chemically induced materials modification at elevated temperatures.





Also in the lab:
- SpecPack scanning spectroscopy software
- UV-VIS Acousto-Optical Modulator
- Stanford Research DG535 pulse generator
- Agilent 33220A arbitrary waveform generator
- Perkin-Elmer Avalanche Photodiode
- Newport ESP300 controller, rotation, and translation stages