Electro-Optic / Acousto-Optic Detectors

BTC uses photo-EMF and photo-refractive detector technologies. Using these technologies, Brimrose has shown significant improvement in sensitivity of acoustic sensors using pulsed laser sources. Applications include remote laser vibrometry and laser microphone.


Colloidal quantum dots technology

Colloidal quantum dots (CQDs) have dimensions on the nanometer scale and contain hundreds to thousands of atoms. CQDs that have a radius on the same size or smaller than the excitonic Bohr radius of the material will display quantum confinement phenomena. (Once they reach the size of the excitonic radius they will take on bulk properties.) In general, the larger the CQDs the smaller the band gap (the larger the cutoff wavelength). As opposed to mercury-based traditional devices, where tuning of the spectral range is accomplished by selection of the stoichiometry of the constituent atoms, CQDs are optically tuned by adjusting the size of the core grains during synthesis. MWIR response requires monodispersed CQDs with sizes in the range of 10 nm to 15 nm.  LWIR response requires monodispered CQD with sizes in the range of 18 nm to 22 nm. Such a large size requires that HgTe CQDs be dissolved/dispersed in a suitable solution without settling down or precipitating out during processing to build devices.

Recent advances in narrow-band-gap CQDs have shown great promise for achieving low-power, low-cost and un-cooled SWIR, MWIR, and LWIR detection. BTC has demonstrated a CQD- based focal plane array (FPA) and camera, operating in the wavelength range of 0.9 um to 1.7 um at room temperature. CQD-based MWIR detection has been developed only at discrete single pixel level only (with some cooling).

  Figure 1. TEM images of HgTe CQDs and sample absorption spectra

Figure 1. TEM images of HgTe CQDs and sample absorption spectra

Brimrose Technology has extensive experience and expertise in the area of II-VI semiconductor CQD synthesis and LWIR detector fabrication using narrow-band-gap semiconductor materials. We have established facilities for CQD research and since 2006 have had two scientists working in the development of CQD materials.

  Figure 2. TEM Images of HgTe QD synthesized in oleylamine (1021) and with the addition of mercaptoacetic acid (1022). Absorption spectra of the HgTe QDs (right).

Figure 2. TEM Images of HgTe QD synthesized in oleylamine (1021) and with the addition of mercaptoacetic acid (1022). Absorption spectra of the HgTe QDs (right).


X-RAY DETECTION / MERCUROUS BROMIDE (Hg2Br2)

Brimrose Technology Corporation has developed rugged, portable, low-cost and very-high-performance detectors based on a completely new class of material, mercurous bromide (Hg2Br2), that can detect both gamma radiation and neutron particles. Hg2Br2 is a room temperature, wide-band-gap (3.1eV), semiconductor material that offers many advantages over existing detector technologies. First, the material is similar to its related bivalent mercuric compound HgI2, whose gamma detector performance has been known to be comparable to or even better than CZT (which in turn, has been known to be better than LaBr3), Hg22Br2 has the same potential but with many additional advantages such as being non-hygroscopic, non-toxic and very stable for long-term operation. It is much easier to grow in larger volume compared to HgI2 due to the fact that it has no phase transition, unlike HgI2. It is mechanically stronger than HgI2, has much higher density (7.3 g/cm3 compared to 6.4 g/cm3) and hence higher stopping power and efficiency. Thus it could be much more practical and economical for large-volume-detector manufacturing.
 
Hg2Br2 Crystal Boule
Hg2Br2 Crystal Boule Grown at Brimrose by PVT
Detector- Configuration

Detector Configurations

 
Additionally, like HgI2, Hg2Br2 also has the potential for thermal neutron detection. BTC has demonstrated the feasibility of mercurous bromide Hg2Br2 material as a practical and reliable advanced detector material that can deliver enhanced performance in nuclear radiation detection technology. We use a proprietary growth procedure to produce large high quality Hg2Br2 crystals up to 2” in diameter and 3” in length. (we are the only company in the country currently capable of growing these large crystals). Ground-breaking energy resolution of less than 2% at 60 keV Am-241 gamma and less than 1% at 662 keV at room temperature were observed which is comparable to or better than that of state-of-the-art CZT radiation detectors. Theoretical calculations via numerical simulation also confirmed the great potential of this novel material.

Photo-EMF *

Photo-EMF sensors operate on the basis of the formation of internal electric space charge fields that are formed inside photoconductive semiconductors when they are illuminated by an optical interference pattern. The moving space charge field results in a net photocurrent output from the material even when there is no external electric field. These photocurrents can be used to deduce information about the optical frequency spectrum of the optical fields that form the interference pattern. These photo-EMF sensors, as they are called, can be used in various applications such as highly precise velocimeters and vibrometers.

Photo-EMF

Schematic of Experimental Arrangement for The PPLV for Human Life Signs Detection.

At BTC, one of our primary applications for this technology is the use of photo-EMF pulsed laser vibrometers to measure human life signs. With such a high sensitivity in surface displacement measurement and tolerance to optical speckles, the photo-EMF pulsed laser vibrometer (PPLV) is an ideal device to monitor the life signs of humans and other biological subjects.

These measurements can be taken from essentially any part of the body, with or without clothing, and without requiring any surface pre-treatments like the attachment of retroreflective tapes or deployment of specialelectronic filtering in order to eliminate the sudden dropoffs in the vibrometer output.

We have demonstrated the use of PPLV to detect the heartbeats, respirations, and gross physical movement of human subjects.

References:

  • Wang, Sudhir B. Trivedi, Feng Jin, Sergei Stepanov, Zhongyang Chen, Jacob Khurgin, Ponciano Rodriguez and Narasimha Prasad. IEEE Sensors Journal, Vol. 7, No. 9 (2007) 1370.

  • C. C. Wang, S. B. Trivedi, F. Jin, Z. Chen, J. Khurgin, P. Rodriguez, and N. Prasad. “Biological Life Signs Detection Using High Sensitivity Pulsed Laser Vibrometer,” invited paper, CLEO, Baltimore, MD, May 2007.