A Pacific brittle star Ophiura sarsii has previously been shown to produce a chlorin (3S,4S)-14-Ethyl-9-(hydroxymethyl)-4,8,13,18-tetramethyl-20-oxo-3-phorbinepropanoic acid (ETPA) (1) with potent phototoxic activities, making it applicable to photodynamic therapy. Using extensive LC-MS metabolite profiling, molecular network analysis, and targeted isolation with de novo NMR structure elucidation, we herein identify five additional chlorin compounds from O. sarsii and its deep-sea relative O. ooplax: 10S-Hydroxypheophorbide a (2), Pheophorbide a (3), Pyropheophorbide a (4), (3S,4S,21R)-14-Ethyl-9-(hydroxymethyl)-21-(methoxycarbonyl)-4,8,13,18-tetramethyl-20-oxo-3-phorbinepropanoic acid (5), and (3S,4S,21R)-14-Ethyl-21-hydroxy-9-(hydroxymethyl)-4,8,13,18-tetramethyl-20-oxo-3-phorbinepropanoic acid (6). Chlorins 5 and 6 have not been previously reported in natural sources. Interestingly, low amounts of chlorins 1-4 and 6 could also be identified in a distant species, the basket star Gorgonocephalus cf. eucnemis, demonstrating that chlorins are produced by a wide spectrum of marine invertebrates of the class Ophiuroidea. Following the purification of these major Ophiura chlorin metabolites, we discovered the significant singlet oxygen quantum yield upon their photoinduction and the resulting phototoxicity against triple-negative breast cancer BT-20 cells. These studies identify an arsenal of brittle star chlorins as natural photosensitizers with potential photodynamic therapy applications.

The detailed analysis of the sum-over-state formula for the entanglement induced two-photon absorption (ETPA) transition moment shows that the magnitude of the ETPA cross-section is expected to vary significantly depending on the coherence time Te and the relative position of just two electronic states. Moreover, the dependency on Te is periodic. These predictions are confirmed by molecular quantum mechanical calculations for several chromophores.

Much of our progress in understanding microscale biology has been powered by advances in microscopy. For instance, super-resolution microscopes allow the observation of biological structures at near-atomic-scale resolution, while multi-photon microscopes allow imaging deep into tissue. However, biological structures and dynamics still often remain out of reach of existing microscopes, with further advances in signal-to-noise, resolution and speed needed to access them. In many cases, the performance of microscopes is now limited by quantum effects -- such as noise due to the quantisation of light into photons or, for multi-photon microscopes, the low cross-section of multi-photon scattering. These limitations can be overcome by exploiting features of quantum mechanics such as entanglement. Quantum effects can also provide new ways to enhance the performance of microscopes, such as new super-resolution techniques and new techniques to image at difficult to reach wavelengths. This review provides an overview of these various ways in which quantum techniques can improve microscopy, including recent experimental progress. It seeks to provide a realistic picture of what is possible, and what the constraints and opportunities are.

We experimentally study entangled two-photon absorption in Rhodamine 6G as a function of the spatial properties of a high flux of broadband entangled photon pairs. We first demonstrate a key signature dependence of the entangled two-photon absorption rate on the type of entangled pair flux attenuation: linear, when the laser pump power is attenuated, and quadratic, when the pair flux itself experiences linear loss. We then perform a fluorescence-based Z-scan measurement to study the influence of beam waist size on the entangled two-photon absorption process and compare this to classical single- and two-photon absorption processes. We demonstrate that the entangled two-photon absorption shares a beam waist dependence similar to that of classical two-photon absorption. This result presents an additional argument for the wide range of contrasting values of quoted entangled two-photon absorption cross-sections of dyes in literature.

Nonlinear spectroscopy and microscopy techniques are ubiquitous in a wide range of applications across physics and biology. However, these usually rely on high-powered pulsed laser systems. A promising alternative is to exploit entangled two-photon absorption (ETPA), which can lead to tens of orders of magnitude lower incident fluxes than in conventional two-photon absorption schemes. However, the role of different entangled degrees of freedom in ETPA was unclear following recent experimental studies, when compared to earlier theoretical works. Here, we first demonstrate a linear dependence of the ETPA rate with the photon-pair rate, a clear signature of ETPA, and estimate the values for the concentration-dependent ETPA cross section for Rhodamine 6G. We then investigate the signature of energy-time entanglement and polarization dependence in the ETPA fluorescence rate and demonstrate a strong dependence of the signal on the interphoton delay that reflects the coherence time of the entangled two-photon wave packet.

In this paper we demonstrate first, to the best of our knowledge, experimental characteristics of tunable pulsed bulk laser on 3-(diethylamino)-7-imino-7H-[1]benzopyrano[3’,2’:3,4]pyrido[1,2-a]benzimidazol-6-carbonitril (Chromene-3) and 4,4-difluoro-1,3,5,7,8-pentamethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (PM-567) dyes in polymethyl methacrylate (PMMA) – tuning range and optimal dye concentrations in polymer matrix, from lasing efficiency and tuning range point of view.

Quantum imaging with undetected photons is recently appeared promising brunch of quantum optics. Due to properties of photon pairs (signal and idler), generated via spontaneous down-conversion (SPDC) process and phenomenon of induced coherence, one can obtain phase or intensity image of object without detecting of the photon, interacting with it. The theoretical treatment and limitations of such a system with an only crystal and increased brightness are given.

Results of investigation of lasing of epoxy polymer compositions with phenalemine 512 and ZnO nanoparticles are given. It is shown that incorporation of ZnO nanoparticles affects the lasing efficiency without reducing the operating lifetime. The material is promising for the development of laser-active media.