The HighFinesse Linewidth Analyzer 1k series is the ultimate high-end instrument for measuring, analyzing, and controlling frequency and intensity noise of lasers. This device allows users to conduct analysis of frequency noise density, optical lineshape and relative intensity noise with evaluation of intrinsic and effective linewidth. The extremely fast analysis provides real time measurement and evaluation of noise sources such as servo bumps and frequency drifts. In this demo we demonstrate how to use the LWA-1k 1550 in three different modes – time series, noise, and lineshape analysis. In the time series mode, the digitizer settings are used to adjust he time scale and analyze the linewidth at specific points. In the noise analysis, we measure the intrinsic linewidth and we demonstrate how to find sources of noise to eliminate. Finally, we show how lineshape mode can be used to achieve laser modulation and frequency adjustments to broaden or narrow the linewidth.
Terahertz (THz) time-domain spectroscopy systems permit the measurement of a tissue’s hydration level. This feature makes THz spectrometers excellent tools for the noninvasive assessment of skin; however, current systems are large, heavy and not ideal for clinical settings. We previously demonstrated that a portable, compact THz spectrometer permitted measurement of porcine skin optical properties that were comparable to those collected with conventional systems. In order to move toward human use of this system, the goal for this study was to measure the absorption coefficient (μ a ) and index of refraction (n ) of human subjects in vivo. Spectra were collected from 0.1 to 2 THz, and measurements were made from skin at three sites: the palm, ventral and dorsal forearm. Additionally, we used a multiprobe adapter system to measure each subject’s skin hydration levels, transepidermal water loss, and melanin concentration. Our results suggest that the measured optical properties varied considerably for skin tissues that exhibited dissimilar hydration levels. These data provide a framework for using compact THz spectrometers for clinical applications.
Terahertz time-domain spectroscopy (THz-TDS) systems are capable of detecting small differences in water
concentration levels in biological tissues. This feature makes THz devices excellent tools for the noninvasive assessment
of skin; however, most conventional systems prove too cumbersome for limited-space environments. We previously
demonstrated that a portable, compact THz spectrometer permitted measurement of porcine skin optical properties that
were comparable to those collected with conventional systems. In order to move toward human use of this system, the
goal for this study was to collect the optical properties, specifically the absorption coefficient (μa) and index of refraction
(n), of human subjects in vivo. Spectra were collected from 0.1-2 THz, and measurements were made on the palm,
ventral (inner) and dorsal (outer) forearm. Prior to each THz measurement, we used a multiprobe adapter system to
measure each subject’s skin hydration levels, transepidermal waterloss (TEWL), skin color, and degree of melanin
pigmentation. Our results suggest that the measured optical properties were wide-ranging, and varied considerably for
skin tissues with different hydration and melanin levels. These data provide a novel framework for accurate human
tissue measurements using THz spectrometers in limited-space environments.
Terahertz spectrometers and imaging systems are currently being evaluated as biomedical tools for skin burn assessment. These systems show promise, but due to their size and weight, they have restricted portability, and are impractical for military and battlefield settings where space is limited. In this study, we developed and tested the performance of a compact, light, and portable THz time-domain spectroscopy (THz-TDS) device. Optical properties were collected with this system from 0.1 to 1.6 THz for water, ethanol, and several ex vivo porcine tissues (muscle, adipose, skin). For all samples tested, we found that the index of refraction (n) decreases with frequency, while the absorption coefficient (μa) increases with frequency. Muscle, adipose, and frozen/thawed skin samples exhibited comparable n values ranging between 2.5 and 2.0, whereas the n values for freshly harvested skin were roughly 40% lower. Additionally, we found that the freshly harvested samples exhibited higher μa values than the frozen/thawed skin samples. Overall, for all liquids and tissues tested, we found that our system measured optical property values that were consistent with those reported in the literature. These results suggest that our compact THz spectrometer performed comparable to its larger counterparts, and therefore may be a useful and practical tool for skin health assessment.
Terahertz (THz) radiation is increasingly being used in biomedical imaging and spectroscopy applications.
These techniques show tremendous promise to provide new sophisticated tools for the improved detection of skin
cancer. However, despite recent efforts to develop these applications, few studies have been conducted to characterize
the optical properties of skin at THz frequencies. Such information is required to better understand THz-tissue
interactions, and is critical for determining the feasibility of proposed applications. In this study, we have developed and
tested a THz time-domain spectroscopy system. We used this system to acquire the optical properties for fresh and
frozen/thawed excised porcine skin from 0.1 to 2.0 THz. Results show that the index of refraction (n) for both frozen and
fresh skin decreases with frequency. For frozen skin, n equals 2.5 at 0.1 THz and 2.0 at 2.0 THz, and for fresh skin
equals 2.0 at 0.1 THz and 1.7 at 2.0 THz. Values for the absorption coefficient (μa) increase with frequency for both
frozen and fresh skin. Frozen skin exhibits μa values equal to 56 cm-1 at 0.1 THz and 550 cm-1 at 2.0 THz, whereas fresh
skin exhibits values of 56 cm-1 at 0.1 THz and 300
cm-1 at 2.0 THz. Assuming the optical penetration depth (δ) is
inversely proportional to μa (absorption-dominated interactions), THz radiation has limited δ in skin (200 μm at 0.1 THz
to 40 μm at 2.0 THz). These results suggest that applications exploiting THz radiation show the most promise for
investigating superficial tissues.