GEMINI Interferometers
Is it possible to reduce the spectral bandwidth to decrease the measurement time?
No, due to the employed Fourier-transform approach, there is no trade off between the working spectral range and the measurement time. Therefore, you cannot save time by reducing the spectral bandwidth of interest. In fact, the measurement time is affected by the spectral resolution that you want to achieve, i.e. the better the spectral resolution, the longer the scan of the interferometer and thus the measurement time.
Can the GEMINI select a specific spectral band?
No, the GEMINI does not act as a monochromator, so it is not possible to select a single wavelength at the output, given a broad spectrum in the input.
The GEMINI Interferometer always transmits the entire spectrum of the incoming light, introducing a spectral modulation with a period that depends on the delay of the interferometer. For more information on the working principle of the device, please refer to this video.
Does the GEMINI work with coherent (i.e. lasers) or incoherent (i.e. lamps, fluorescent samples) light sources?
The GEMINI Interferometer can work in both cases, with the very same software and optical alignment.
Can I perform experiments with ultra-short laser pulses using the GEMINI?
If the GEMINI is placed “after the sample” (i.e. when the light has already interacted with the sample), then it is possible to use it with ultra-short laser pulses, as it does not affect the temporal resolution of your experiment. As an example, you can refer to this application in pump-probe spectroscopy.
Instead, if you need to use the interferometer “before the sample”, then the GEMINI-2D is the most suitable device. As an example, the GEMINI-2D is used in bidimensional electronic spectroscopy (2DES), in which it creates two replicas of ultra-short pump pulses with a precise control on the dispersion.
How to choose the most suitable version of GEMINI for my application?
– Spectral coverage
The standard model of GEMINI covers the range 250 nm – 2300 nm. There is the option of upgrading it to cover a much broader region (250 nm – 3500 nm).
On request, GEMINI can be customized to cover the 500 nm – 4200 nm range.
Moreover, currently NIREOS is developing a special version of GEMINI, which can work up to 15 microns. Stay tuned for updates on this version!
– Speed
You can select one out of two versions of the driver that controls the relative delay between the two generated replicas of light (“standard” and “high performance – HP”). With respect to the standard controller, the HP version guarantees a higher speed of the scan (up to 5 time faster: it typically takes 15-20 millisecond per step in a step-scan mode) and a much higher accuracy and stability in the relative delay (on the order of 1 attosecond – that is more than 1000 times better than the optical cycle of visible light). This ultimately translates into a much better signal to noise ratio of the retrieved spectrum of your signal.
When GEMINI is coupled to SPAD, APD or PMT detectors and TCSPC systems to detect time-resolved and very weak signals, we always recommend to go for the HP version.
– Spectral resolution
You can select one out of two versions (S, L) with different spectral resolutions:
Please note that this is the minimum achievable spectral resolutions for each version; if sometimes you do not need such a good spectral resolution, you can perform shorter – and thus faster – scans (these parameters can be easily selected via software) and get a worse spectral resolution.
How to couple the GEMINI with time-correlated single-photon counting (TCSPC) modules?
If you are interested in measuring time- and frequency- resolved fluorescence (TRES), we can provide a plug&play software that directly enables the control of both the GEMINI and the TCSPC card, so that you can easily acquire a TRES map without any extra effort for integration.
NIREOS is collaborating with the major TCSPC module providers and the software is compatible with most of the available TCSPC modules on the market.
Contact us to discuss how GEMINI could enrich your time-resolved applications, adding the spectral resolution to your experiments!
Is there a dedicated Software? How does it work?
The GEMINI comes together with a plug&play software, which allows one to easily control the device, acquire the data of interest and retrieve the calibrated spectrum of the light. The software is open access and described by a detailed manual, so that it can be freely modified by the user according to his needs. Moreover, NIREOS team is always available to help the user for customization, if needed.
The software is available in LabVIEW.
For more information concerning the software for TSCPC applications, please refer to the Question “How to couple the GEMINI with time-correlated single-photon counting (TCSPC) modules?”
How does the Optical Alignment work?
The GEMINI Interferometer has a 10 mm clear aperture, and the light inside the device propagates in free space. The most efficient way to use the GEMINI is to enter with collimated light in free space. If one uses optical fibers, then it is possible to use fiber couplers before and/or after the GEMINI.
The optical alignment of the GEMINI is straightforward, as you just need to insert it into the beam path in your setup. There are 2 apertures (1 in the input and 1 in the output surface) with variable diameter, in order to facilitate the optical alignment in the center of the clear aperture; once aligned, the apertures should be completely opened to ensure the maximum throughput.
Which is the provided Spectral Resolution?
The spectral resolution provided by the GEMINI Interferometer is not constant as a function of wavelengths, but it increases at longer wavelengths. This behavior is due to both the Fourier Transformation approach and the birefringence, which depends on the wavelength.
Please refer to the following graph:
The graph above shows the best spectral resolution achievable by the two standard versions of the GEMINI Interferometer. However, the GEMINI offers the ability for customers to adjust the spectral resolution simply via software: the user can even decide to perform faster measurement with poorer spectral resolution. A change in the spectral resolution does not affect the throughput of the device.
HERA Hyperspectral Camera
How many Spectral Bands does it measure?
As HERA does not employ spectral filters or dispersive elements to direct the different colors of the incoming light to the different pixels of a sensor, it is not possible to determine the exact number of spectral bands. In fact, as the spectrum at each pixel of the image is the Fourier Transformation of the interference signal, the spectrum is a continuous function (or curve). Of course, when plotting the data, one needs to sample the spectrum with a proper number of points…but please note that does not affect the spectral resolution of the measurement and it is not an indication of the number of spectral bands!
The “real” answer to this question is that one needs to refer to the spectral resolution provided by the camera, rather than to the number of spectral bands.
Which is the illumination requirement?
Due to its extremely high sensitivity, HERA can work under low-light illumination conditions. This advantage is a consequence of the Fourier transform approach, as the employed interferometer (and the absence of the entrance slit) guarantees a much higher throughput compared to the dispersive- or grating-based technologies.
The camera is therefore very well suited in those applications in which intense and powerful illumination sources are not allowed, as they would damage the sample, such as in biology or cultural heritage. For example, HERA hyperspectral camera is so sensitive that it can measure hyperspectral images of the fluorescence signal emitted by a sample.
How does the Software work?
HERA comes with two software packages: one to acquire the hyperspectral images, see a preview of the measured data and save the measurement to your PC, and the other for a deeper data analysis. You can also export the hyperspectral data-cube in ENVI format.
As the hyperspectral data are heavy files, we strongly suggest to employ a computer with at least 16 Gb RAM and SSD drive.
How to calculate the Spatial Resolution?
HERA employs a 1.3 MP internal sensor and a 25 mm objective, providing 16° FOV. The working range varies from 25 cm to infinity. As an example, the lateral field of view of a scene at 1 m distance corresponds to: 2*tan(8°)*1 m = 28 cm.
Which is the typical Measurement Time?
HERA requires a few tens of seconds to capture the image of the scene and prepare the hyperspectral data-cube. Under low illumination conditions, acquisition time could be longer. During this time, the sample and the camera should remain static with respect to each other.
Also, the spectral resolution (which can be easily set via software) affects the measurement time: the better the spectral resolution, the longer the measurement time.
Is HERA a push-broom or a snapshot hyperspectral camera?
HERA is not a push-broom nor a snapshot hyperspectral camera. Instead, HERA is based on a patented Fourier-Transform approach, guaranteeing an extremely high throughput and sensitivity.
HERA works with a “staring” modality: it can be mounted on a tripod or clamped on an optical table, and there is no need to move the sample in order to acquire the hyperspectral image.
The acquisition software (provided together with the camera) automatically controls the movement of the interferometer during the acquisition, directly providing the user with the calibrated hyperspectral image.
Demo Units
Can I receive a demo unit?
Yes! NIREOS is keen to provide demo units to users that would like to test our products.
Please contact us to schedule a technical call for discussing possible implementation of our devices in your setups, or to plan a demo at your facility!