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In aperiodically poled quasi-phase-matching (QPM) crystals, parametric down-conversion (PDC) can generate very broadband pulsed squeezed light. This is because each part of the crystal will generate squeezed light at a different frequency [1]. But the emission will be thus inhomogeneously broadened, and one requires special measures to eliminate the chirp accompanying the pulses. This can be done...
Melanoma skin cancer is one of the most lethal types of cancer due to comparably early development of metastasis. As preventative medical check-up, optical inspection using polarized light (dermoscopy) is the gold standard in medical practise. If a lesion is diagnosed to be suspicious, it is subsequently excised by a surgeon and analysed by means of histopathology. However, optical inspection so far...
The use of optical frequency combs (FC) for high precision measurements is limited by fluctuations of the comb structure [1]. The FC fluctuations can be modelled as uncoupled noise modes associated with a few global parameters namely power, central wavelength, carrier-envelope offset (CEO) phase, repetition rate, dispersion [2, 3]. However, the correlations between phase and amplitude noises, which...
Quantum-electrodynamics (QED) theory has been tested with high accuracy [1]. However, QED tests in atomic hydrogen are currently limited by the experimentally determined value of the proton charge radius. Therefore spectroscopic measurements were conducted with muonic-atoms (μH and μD) to determine the proton and the deuteron charge radii with an order of magnitude higher accuracy. However, these...
Harmonic mode-locking of a solid-state bulk laser combines the benefits of long resonators with large pulse energy and high repetition rates. With this technique it is possible to operate a system at different repetition rates without changing the optical setup. The signal to noise ratio of a fundamentally mode-locked oscillator is typically much better than in harmonic operation [1]. In this contribution...
A precise control of the electric field nodes relative to the maximum of the intensity envelope is a prerequisite for attosecond pulse generation and experiments in high-field physics [1]. Many carrier-envelope phase (CEP) stabilization schemes start with stabilization of an oscillator, which is nevertheless often difficult to obtain as the CEP has proven highly sensitive to environmental parameters,...
We report on metrological-grade saturated absorption spectroscopy of CHF3 at 8.63 μm based on CW distributed-feedback QCL laser and a mid-IR self-frequency referenced optical comb. The experimental setup for the saturation spectroscopy of CHF3 is shown in Fig. 1. A CW DFB-QCL with a maximum output power of ∼40 mW tunable in the wavelength range from 8.55 to 8.65 μm, in coincidence with the us (asymmetric...
On the Earth, oxygen molecules are generated mostly via the photosynthesis by green plants and algae from carbon dioxide and water: nCO2 + nH2O light→ (CH2O)n + nO2 [1]. Although, theoretical studies showed the possibility of O2 production via CO2 fragmentation [2] and experimental investigations achieved the detection of C+ (referring the creation of O2 on the other side) [3], the direct observation...
Large arm length imbalance fibre-based interferometers have shown great potential for laser frequency stabilization and control, with frequency noise power spectral density close to the 10−1 Hz/Hz1/2 level [1]. In order to understand the performance of such frequency stabilization systems, it is important to distinguish the intrinsic noise of the frequency reference, which is ultimately limited by...
Heralded single-photon sources are a standard experimental tool for studying quantum optics and quantum information in few-photon systems. These sources use spontaneous parametric wave mixing to probabilistically emit pairs of photons. One photon of the pair, the heralding photon, is detected to indicate the presence of the other. In theory, the maximal probability of emitting a single pair of photons...
High-peak-field, narrowband terahertz (THz) sources are well suited for compact electron acceleration [1], however, these sources are still under development and yet to reach optimal energies. A high conversion efficiency via difference frequency generation is established by quasi-phase matching in periodically poled lithium niobáte (PPLN). Moreover, to achieve the required mJ-level THz pulses high...
Nowadays, cold atom-based quantum sensors such as atom interferometers are leaving the optical labs [1, 2], thus allowing fundamental physics to be tested in space. The use of different quantum objects such as Potassium (K) and Rubidium (Rb) ultra-cold quantum gases enables tests of the Universality of Free Fall (UFF) [1-4]. While narrow linewidth lasers emitting at 767 nm and 780 nm are used to build...
Microresonator based frequency combs or microcombs have attracted considerable interest in recent years as they would benefit a widespread of applications including high speed communication system, metrology, ultrafast optical clocks and on chip optical signal processing. A great amount of work on microcombs has been done in the past few years; coherent sources based on optical parametric generation...
Widely tunable, narrow linewidth diode lasers have found a wide range of important applications, from terrestrial ones, such as fiber-optic communications [1] or optical sensing [2], to applications in space, for instance in atomic clocks [3]. Monolithic diode lasers for such tasks, i.e., distributed feedback (DFB) lasers and distributed Bragg reflector (DBR) lasers, approach their limits since they...
Using Terahertz (THz) time-domain spectroscopy (THz-TDS), the dispersion of several gases had been measured up to 4.5 THz [1]. From these measurements the refractive index that increases with increasing pressure was obtained over this frequency range. The results follow the Hauf-Grigull relation.
Optical frequency combs from ultrafast lasers have revolutionized the field of optical metrology and photonics. However, today's commercial frequency combs are still based on complex and expensive ultrafast laser systems, which prevent applications for cost-sensitive areas. Among emerging technologies, modelocked semiconductor lasers are highly promising for future low-cost high-volume production...
Techniques for stabilizing the carrier-envelope offset (CEO) frequency of an optical frequency comb are prerequisites for precision spectroscopy. A 2f-to-3f self-referencing interferometer (SRI) requires only a 2/3-octave bandwidth of supercontinuum (SC) light; however, it has not been regarded as a practical method because the conversion efficiency of third-harmonic generation is much lower than...
Recent advances in the design of broadband parametric down-conversion (PDC) sources have opened the possibility to attain a regime of high squeezing previously unacessible in the pulsed domain [1]. However, characterising a PDC source is a challenging task when multiple spectral modes are being squeezed simultaneously and one wants to determine the number of squeezers and their relative strengths...
Sum frequency generation (SFG) spectroscopy is a powerful technique for characterization of vibrational bonds of molecules at surfaces and interfaces [1]. The principle of SFG is based on resonant nonlinear mixing of two optical pulses — typically one in MIR range and another visible (VIS). There are two main SFG spectroscopy techniques. Narrowband SFG (NB-SFG) is based on picosecond MIR and picosecond...
Vibrational spectroscopy in the mid-infrared (MIR) molecular fingerprint region (∼2–25 μm) provides information on the molecular composition, structure and conformation, affording tremendous potential for advances in fields ranging from fundamental research over security and environmental applications to biology and medicine. Traditionally, broadband measurements in this spectral region are carried...
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