Babu Varghese

• PhD
• Senior Researcher at Philips

We describe a novel, minimally invasive laser technology for skin rejuvenation by creating isolated microscopic lesions within tissue below the epidermis using laser induced optical breakdown. Using an in-house built prototype device, tightly focused near-infrared laser pulses are used to create optical breakdown in the dermis while leaving the epi...

We report the first path-length-resolved perfusion measurements on human skin measured with a phase-modulated low-coherence Mach-Zehnder interferometer with spatially separated fibers for illumination and detection. Optical path lengths of Doppler shifted and unshifted light and path-length-dependent Doppler broadening of multiply scattered light f...

We investigated the influence of thermal initiation pathway on the irradiance threshold for laser induced breakdown in transparent, absorbing and scattering phantoms. We observed a transition from laser-induced optical breakdown to laser-induced thermal breakdown as the absorption coefficient of the medium is increased. We found that the irradiance...

We investigated the influence of polarization and apodization on laser induced optical breakdown threshold in transparent and diffuse media using linearly and radially polarized light. We demonstrate a lower irradiance threshold for optical breakdown using radially polarized light. The dominance of radial polarization in higher-order multiphoton io...

Laser-induced optical breakdown (LIOB) and laser-induced thermal breakdown (LITB) have emerged as new modalities for cutaneous interventions. Both initiate plasma-induced ablation and result into spatially-confined micro-lesions adjacent to intact tissue. This study aimed to demonstrate distinct histological- and clinical effects of LIOB. Histolog...

There is provided a device (100) for treating tissue (102). The device (100) comprises a light source (104) configured to emit light (106) to illuminate the tissue (102). The light source (104) is configured to alternate between emitting light of a first wavelength to stimulate at least partial photoconversion of a protein in at least part of the t...

We describe non-invasive, shortwave-infrared spectroscopy for quantitative profiling of stratum corneum barrier function and wide field reflectance imaging for measurement of skin gloss.

We demonstrate the feasibility of short wave infrared (SWIR) spectroscopy combined with tape stripping for depth profiling of lipids and water in the stratum corneum of human skin. The proposed spectroscopic technique relies on differential detection at three wavelengths of 1720, 1750, and 1770 nm, with varying ratio of the lipid-to-water absorptio...

We witness a rise of commercial systems relying on picosecond pulses for cutaneous interventions. In parallel with this development, a somewhat distinct research prototype also operating in the picosecond regime was described in literature. Albeit both market-available products and the investigational device employ laser beams of nearly the same...

Therapeutic action of light relies on a range of photon–tissue interactions from photochemical, photobiological and photothermal effects to photoablation, plasma-induced ablation, photo-thermo-mechanical disruption and photodisruption. In the recent years we have been witnessing a steep rise in the availability of sub-nanosecond or the so-called pi...

We demonstrate a low-cost optical method for measuring the gloss properties with improved sensitivity in the low gloss regime, relevant for skin gloss properties. The gloss estimation method is based on, on the one hand, the slope of the intensity gradient in the transition regime between specular and diffuse reflection and on the other on the sum...

Optical techniques have made a profound impact on modern medicine, both for diagnostics and for treatment. Therapeutic action of light relies on a range of photon–tissue interactions from photochemical, photobiological and photothermal effects to photoablation, plasma-induced ablation, photo-thermo-mechanical disruption and photodisruption. In the...

Skin barrier function relies on well balanced water and lipid system of stratum corneum. Optimal hydration and oiliness levels are indicators of skin health and integrity. We demonstrate an accurate and sensitive depth profiling of stratum corneum sebum and hydration levels using short wave infrared spectroscopy in the spectral range around 1720 nm...

Background/aims: Sensitive skin (SS), a frequently reported condition in the Western world, has been suggested to be underlined by an impaired skin barrier. The aim of this study was to investigate the skin barrier molecular composition in SS subjects using confocal Raman microspectroscopy (CRS), and to compare it with that of non-SS (NSS) individ...

Fractional photothermolysis uses lasers to generate a pattern of microscopic columnar thermal lesions within the skin stimulating collagen remodeling. In this paper we investigate the use of Bessel beams as an alternative to conventional Gaussian beams in creating laser photothermal lesions of different aspect ratios in skin. We show for the first...

We report a method on quantitative and simultaneous non-contact in-vivo hydration and sebum measurements of the skin using an infrared optical spectroscopic set-up. The method utilizes differential detection with three wavelengths 1720, 1750, and 1770 nm, corresponding to the lipid vibrational bands that lay “in between” the prominent water absorpt...

Skin health characterized by a system of water and lipids in Stratum Corneum provide protection from harmful external elements and prevent trans-epidermal water loss. Skin hydration (moisture) and sebum (skin surface lipids) are considered to be important factors in skin health; a right balance between these components is an indication of skin heal...

Laser induced optical breakdown (LIOB) is a non-linear absorption process leading to plasma formation at locations where the threshold irradiance for breakdown is surpassed. In this paper we experimentally demonstrate the influence of polarization and absorption on laser induced breakdown threshold in transparent, absorbing and scattering phantoms...

Skin health is characterized by heterogeneous system of water and lipids in upper layers providing protection from external environment and preventing loss of vital components of the body. Skin hydration (moisture) and sebum (skin surface lipids) are considered to be important factors in skin health; a right balance between these components is an i...

An optical blade and a hair cutting device is configured to cut a hair near skin of a human body part or animal body part. The optical blade maybe used in a hair cutting device and includes a blade body configured to guide optical radiation, and a tapered end configured to allow the optical radiation to exit the optical blade. The tapered end inclu...

Skin barrier function, confined to the stratum corneum, is traditionally evaluated using established, noninvasive biophysical methods like transepidermal water loss, capacitance and conductance. However, these methods neither measure skin molecular composition nor its structure, hindering the actual causes of skin barrier change or impairment. At t...

A detector for detecting a birefringent object near a skin surface of a human body part or an animal body part includes a source for emitting optical radiation having first and second wavelengths and an incident polarization state. An imaging unit is configured to image the birefringent object near the surface includes a detection unit for detectin...

The polarization characteristics of birefringent tissues could be only partially obtained using linearly polarized light in polarization sensitive optical imaging. Here we analyze the change in polarization of backscattered light from birefringent structures versus the orientations of the incident polarizations using linearly, circularly and radial...

We demonstrate the efficacy of a novel minimally invasive nonthermal skin rejuvenation technique for wrinkle and fine-line reduction based on laser-induced optical breakdown. The optical breakdown caused by tightly focused near-infrared laser pulses creates a grid of intradermal lesions without affecting the epidermis, leading to skin rejuvenation....

Here we describe a method for enhancing the contrast in imaging skin birefringent structures. The method relies on polarization-dependent optical properties and is implemented using cross polarized confocal microscopy. The experimental data obtained using ex-vivo and in-vivo measurements on human scalp hairs and human skin demonstrate a significant...

In laser Doppler measurements, perfusion values averaged over different and basically unknown path lengths are recorded. To facilitate quantitative path length resolved perfusion measurements, we developed a phase modulated Mach-Zehnder interferometer with spatially separated fibers for illumination and detection. The goal of this study is to measu...

Perfusion measurements using conventional laser Doppler techniques are affected by the variations in tissue optical properties. Differences in absorption and scattering will induce different path lengths and consequently will alter the probability that a Doppler shift will occur. In this study, the fraction of Doppler shifted photons and the Dopple...

An increasing number of applications, including non- or minimally invasive diagnostics and treatment as well as various cosmetic procedures, has resulted in a need to determine the optical properties of hair and its structures. We report on the measurement of the total attenuation coefficient of the cortex and the medulla of blond, gray, and Asian...

Laser Doppler flowmetry (LDF) is a non-invasive technique for monitoring blood microcirculation in biological tissues. Skin perfusion measurements using this technique depend not only on the instrumental factors, but also on the extent of interaction of photons with moving red blood cells. Thus for a constant perfusion, the LDF output signal is aff...

The readings in laser Doppler perfusion monitoring are affected by the optical properties of the tissue in which the microvasculature is embedded, through their effect on the optical path lengths. Thus for a constant perfusion, the LDF output signal is affected by the variance in individual photon path lengths due to the changes in tissue optical p...

We report on the dependence of the decorrelation time on the spatial intensity correlation of speckles generated in the far-field by back-scattered photons from turbid media. The effects contribute to an explanation of an earlier observation that the average Doppler width of the power spectrum of detector current fluctuations depends on the size of...

The influence of tissue optical properties on laser Doppler perfusion imaging (LDPI) is not well understood. We address this problem by quantifying the dependence of the signal response to tissue optical properties based on speckles or coherence areas and on photon statistics. We investigate the effect in vivo, showing the amplitude of photocurrent...

We describe an improved method for coherence domain path length resolved measurements of multiply scattered photons in turbid media. An electro-optic phase modulator sinusoidally modulates the phase in the reference arm of a low coherence fiber optic Mach–Zehnder interferometer, at a high phase modulation angle. For dynamic turbid media this result...

Laser Doppler flowmetry is a non-invasive method of measuring microcirculatory blood flow in tissue. In this review the technique is discussed in detail. The theoretical and experimental developments to improve the technique are reviewed. The limitations of the method are elaborated upon, and the research done so far to overcome these limitations i...

The performance of a graded index multimode fiber optic low coherence Mach-Zehnder interferometer with phase modulation is analyzed. Investigated aspects were its ability to measure path length distributions and to perform path length resolved Doppler measurements of multiple scattered photons in a turbid suspension of particles undergoing Brownian...

We show a novel technique to distinguish between Doppler shifted and unshifted light in multiple scattering experiments on mixed static and dynamic media. With a phase modulated low coherence Mach-Zehnder interferometer, optical path lengths of shifted and unshifted light and path length dependent Doppler broadening are measured in a two-layer tiss...

A theoretical model is presented and experimentally validated that allows the prediction of the effect of speckles on the depth sensitivity of laser Doppler perfusion imaging. It is shown that the influence of speckles on depth sensitivity is large. In particular the sensitivity to particle motion in superficial layers is strongly beam diameter dep...

We show experimental validation of a novel technique to measure optical path length distributions and path length resolved Doppler broadening in turbid media for different reduced scattering coefficients and anisotropies. The technique involves a phase modulated low coherence Mach-Zehnder interferometer, with separate fibers for illumination and de...

We present a model for predicting the spatial intensity correlation function of dynamic speckle patterns formed by light backscattered from turbid suspensions, and an experimental validation of these predictions. The spatial correlation varies remarkably with multiple scattering. The provided computational scheme is a step towards correctly interpr...

In optical Doppler measurements, the path length of the light is unknown. To facilitate quantitative measurements, we develop a phase-modulated Mach-Zehnder interferometer with separate fibers for illumination and detection. With this setup, path-length-resolved dynamic light scattering measurements of multiple scattered light in static and dynamic...

We describe path length resolved Doppler measurements of the multiply scattered light in turbid media using phase modulated low coherence Mach-Zehnder interferometer, with separate fibers for illumination and detection. A Doppler broadened phase modulation interference peak observed at the modulation frequency shows an increase in the average Doppl...

We report on a theoretical/experimental model to predict the depth sensitivity of laser Doppler perfusion imager. Further more we show the quantitative influence of speckles on laser Doppler perfusion imager response to scattering at different depths. The model is based on Monte Carlo simulations and experiments on static and dynamic scattering pha...

We describe path length resolved Doppler measurements of the multiply scattered light in turbid media using phase modulated low coherence Mach-Zehnder interferometer, with separate fibers for illumination and detection. A Doppler broadened phase modulation interference peak observed at the modulation frequency shows an increase in the average Doppl...

We report the development of non-invasive, path length resolved Doppler measurements of the multiply scattered light in turbid media, for different absorptions using phase modulated Mach-Zehnder low coherence interferometer, with separate fibers for illumination and detection. A Doppler broadened phase modulation interference peak is observed that...

We show that speckles play an important role in laser Doppler perfusion imaging. The influence of speckles on the signal amplitude and the Doppler spectrum is demonstrated experimentally on particle suspensions with different scattering levels and varying beam width. Polystyrene microsphere suspensions with known optical properties are used to make...

We report on the quantitative influence of speckles in laser Doppler perfusion imaging. The influence of speckles on the signal amplitude and on the Doppler spectrum is demonstrated experimentally for particle suspensions with different scattering levels and various beam widths. It is shown that the type of tissue affects the instrumental response...