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Photonic generation and transmission of Linearly Chirped Microwave Waveform (LCMW) with a high Time-BandWidth Product (TBWP), of the order of 102 or more, is a widely used approach in Synthetic Aperture Radar (SAR) payloads to realize high range resolution, improving the distinction between two or more targets on the same bearing. In standard payload systems, an electronic approach based on voltage-controlled oscillator or digital signal processing, is used as LCMW generator, with both limited TBWP and operating frequency. In this context, a photonic approach plays a crucial role, ensuring low phase noise, high TBWP and operation frequency of the order of GHz, with a significant reduction of mass and size with respect to the electronic counterparts. Here, we propose the design of a Ka-band photonic LCMW generator, based on a frequency-tuneable Opto-Electronic Oscillator (OEO) and a Recirculating Phase Modulation Loop (RPML), with high spectral purity and high chirp rate in a small footprint. The OEO heart is a one-dimensional photonic crystal ring resonator with an ultra-high Q factor value and an optical delay < 10 μs. A low-frequency optical signal, with a high chirp rate and TBWP values of the order of 102-103, is generated in the RPML section.

A broadband photonic microwave signal processor based on integrated dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM) is proposed. The processor has a tunable local oscillator (LO) signal, which is generated by the optoelectronic oscillator (OEO) loop in one of the sub-DPMZM with high spectral purity and low phase noise, and its center frequency can be tuned by electronic band-pass filter (EBPF). Using the bias voltage of DP-DPMZM and fiber Bragg grating, the carrier-suppressed single-sideband (CS-SSB) modulation of LO and RF signals can be realized, and the up or down conversion of frequency converter can be realized by adjusting the single bias voltage of DP-DPMZM. Moreover, the power fading caused by dispersion is well compensated with the SSB modulation. The experimental results show that the tunable LO signal of 6-20 GHz is successfully generated, the side mode rejection ratio is as high as 48.4 dB, and the 10 kHz phase noise is 107.6 dBc/Hz at 8 GHz. The spurious rejection ratio of up-down conversion signal is 31.4 dB and 33.6 dB, respectively.

Mid-infrared semiconductor lasers have emerged as indispensable compact coherent sources for military and commercial applications. While much of the historical emphasis has been on maximizing the output power and/or spectral purity, a recent new focus has been on engineering these lasers to operate as optical frequency combs (OFCs) for broadband real-time spectroscopy. In particular, the combination of low-drive-power and broad gain bandwidth has made interband cascade laser (ICL) OFCs an attractive complement to quantum cascade laser OFCs operating at longer wavelengths. Moreover, ICL combs can potentially be incorporated into fully-integrated dual-comb spectrometers that employ fast, room-temperature IC photodetectors processed on the same chip. However, the high refractive index of the ICL’s GaSb substrate poses some challenges to the optical waveguiding. Because the modal index is considerably lower than that of the substrate, the optical field can penetrate the bottom cladding layer and leak into the GaSb, inducing wavelength-dependent interference that modifies the gain and group velocity dispersion (GVD) profiles. Even when the effect on lasing threshold is small, the comb properties can be adversely affected. Using the sub-threshold Fourier transform technique, we studied ICL combs with various ridge widths, substrate thicknesses, and center wavelengths. This allowed us to evaluate the effects of modal leakage on the GVD. We find that the resonant nature of the substrate modes induces oscillations, which affect both the spectral bandwidth and the phase-locking properties above threshold. Strategies to mitigate the GVD’s undesired and unpredictable spectral variation will be presented.

Recent progress in developing tunable mid-IR (2.6 um range) integrated hybrid lasers, are demonstrated. the hybrid laser includes gain chips based on AlGaInAsSb/GaSb quantum wells and tunable reflectors based on micron-scale silicon on insulator integrated photonics platform. The devices exhibit milliwatt-level average power, 10 mW of peak powers and tuning ranges up to 60 nm. Factors limiting tuning range, spectral purity and maximum power are discussed. The demonstrated platform enables realization of tunable lasers for a wide range of applications requiring high performance light sources with emission wavelengths from 1.8 µm to 3 µm and beyond.

Infrared spectroscopy is a powerful tool for identification and quantification of functional molecular groups. Molecular gas lasers have long been used for such purposes due to their early development and mature manufacturing technology. Over the past few decades, Quantum Cascade Lasers (QCLs) have popularized due to their continuously tunable wavelength, climbing peak power, and steadily improving manufacturing economics. However, for many applications in the longwave infrared (LWIR) spectral region, carbon dioxide (CO2) lasers retain a clear advantage over QCLs by providing higher power, greater spectral purity and extended coherence length. This combination allows for detection of volatile organic compounds indicative of many diseases such as early-stage lung cancer, an advanced prognosis of which can increase the 5-year survival rate by 37.5%. In addition to medical applications, CO2 lasers also retain their niche in environmental sensing by providing a robust photoacoustic airborne measurement platform for air quality and climate research. Furthermore, recent advances in thermally balanced gas laser architectures have enabled reliable mobile leak monitoring of the insulation gas Sulfur Hexafluoride (SF6) used in medium to ultra-high-voltage electricity transmission lines. With the installed base of SF6 expected to grow 75% by 2030 due to the increase of green energy infrastructure via solar panels and wind turbines – both of which rely on electrical connections, switches, and circuit breakers – this task has gained new urgency due to an upper leak estimate of 15% over the full life cycle of the insulation gas.

Narrow linewidth laser diodes (LDs) emitting in the near-UV (NUV) are gaining attention for applications ranging from spectroscopy to atom cooling and interferometry or other applications requiring high spectral purity. InGaN edge-emitting LDs can exhibit a power of hundreds of mW in an unstable multimode regime detrimental to aforementioned uses. In this paper we report on a compact and robust design based on a low-cost blue LD, a beam shaping optical system and a fiber Bragg grating (FBG) acting as a wavelength selective reflector. One longitudinal mode of the non-antireflection coated laser diode is selected by a close to 30 pm bandwidth FBG allowing a few mW output power around 400 nm and a sidemode- suppression-ratio approaching 50 dB exceeding our last published results. Our previous studies showed that a single-frequency regime with a sub-MHz integrated linewidth and an estimated intrinsic linewidth of 16 kHz was possible by a carefully engineered external cavity. We will study the influence of the cavity length with different fiber types (SM or PM). Assessment will focus on the linewidth and a detailed intensity and frequency noise analysis of the emission. We will also investigate for the first-time the stability of several types of UV-FBG submitted to tens of mW of 400 nm light guided into the fiber core. This work demonstrates state-of-the-art performances by connecting low-cost components and opens the way to the fabrication of highly coherent laser sources that could meet the markets for the NUV applications.

Recently, imec has installed and commissioned an industrial, ultrafast EUV materials characterization and lithography lab, imec’s AttoLab, with a primary aim to explore limits of photoresist performance and their associated ultrafast chemistries. Here, we demonstrate, for the first time, the use of a table-top, high-harmonic EUV system (KM Labs, XUUS4) to perform interference lithography of sub-22-nm pitch patterns in an Inpria MOx resist via a Lloyd’s mirror interference lithography (IL) tool. Analysis of SEM images enables us to identify potential sources of image blur, which we attribute to out-of-sync vibrations, flare, spectral purity, and laser stability. Nevertheless, these results confirm the ability of table-top, high-harmonic EUV sources to print lithographic patterns below a 22-nm pitch. In future work, we plan to investigate sub-20-nm patterning in different resist formulations, as well as expand the lithographic capabilities in AttoLab to perform IL on full 300-mm wafers.

In a conventional semiconductor laser, light reciprocates in the lateral direction and resonates by the light-emitting region laid in the horizontal direction. Although the horizontal length is as small as 0.3 mm, it is still 300 times as large as the light wavelength of 0.001 mm. Therefore, analogous to a musical instrument, many harmonics appear, and the spectral purity of the light is lost. As will be described in detail later, this horizontal cavity laser (abbreviated as a stripe laser) could not be manufactured by a monolithic process by thin film formation such as a semiconductor large-scale integrated (LSI) circuit. Therefore, let us compare the conventional horizontal cavity semiconductor laser and the VCSEL, and consider why it is a surface emitting laser.

Fluorescent probes are widely used in biological imaging; however, their spectral properties often limit sensing and multiplexing. Instead, intracellular lasers, offer increased spectral purity, photostability and distinct spectral outputs enabling the unique tagging of multiple cells over long time periods. Here we report on the optimisation of low threshold miniature lasers, 1000-fold smaller than the eukaryotic nucleus (Vlaser

With the introduction of the NXE:3400B scanner, ASML has brought EUV to High-Volume Manufacturing (HVM). The high EUV power of >200W being realized with this system satisfies the throughput requirements of HVM, but also requires reconsideration of the imaging aspects of spectral purity, both from the details of the EUV emission spectrum and from the DUV emission. This paper will present simulation and experimental results for the spectral purity of high-power EUV systems, and the imaging impact of this, both for the case of with and without a pellicle. Also, possible controls for spectral purity will be discussed, and a novel method will be described to measure imaging impact of varying CE and DUV. It will be shown that CE optimization towards higher source power leads to reduction in relative DUV content, that the small deltas in EUV source spectrum for higher power do not influence imaging. It will also be shown that resulting variations in DUV do not affect imaging performance significantly, provided that a suitable reticle black border is used. In short, spectral purity performance is not a bottleneck for increasing power of EUV systems to well above 250W.

We demonstrate 104 Watts of in-band output power from a cascaded Raman fiber laser operating around 1.7 μm with a spectral purity of over 90% operating in both continuous wave and pulsed regimes. Through the use of a filter fiber with its cutoff wavelength designed between the 6th and 7th Stokes orders, output above 1.8 μm is suppressed below threshold values. In the pulsed regime the laser produces output pulses ranging from 11.5 mJ pulses with 100 μs pulse width to 10 J pulses with 100 ms pulse width.

We provide an overview on THz frequency metrology, starting from the nowadays available continuous wave THz sources, discussing their main features such as tunability, spectral purity and possibility of frequency referencing to the primary frequency standard. A comparison on the achieved results in high precision molecular spectroscopy is given and discussed, and finally a special emphasis is placed on the future developments of this upcoming field. In fact, particular attention will be given to new generation metrological-grade THz sources, such as a novel 3-octaves-spanning roomtemperature continuous-wave source based on difference frequency generation, and the latest developments regarding quantum cascade laser frequency combs based on four-wave-mixing nonlinear processes.

This article reports the development of 200-mW 1.55-μm DFB laser module with RIN below -162 dB/Hz which are well suited for microwave photonics or free space optical communication applications. Specific design has allowed reaching high power (>300 mW), low noise and high spectral purity laser chip. The chip has been packaged in Butterfly module optimized for reducing the module power consumption. DFB laser module system validations have been done on three laboratory test-beds representative of target applications, namely high-frequency optical LO distribution, photonic RF frequency conversion, and free space optical communication links.

Two important challenges in quantum photonics are to generate useful states with high fidelity, and to detect them and verify their properties. Particularly valuable states are single photons and entangled photon pairs in well-defined optical modes, as they can be used in many quantum information protocols or used to build up more complex states. For sources, we employ integrated nonlinear optics (waveguides in lithium niobite and potassium titanyl phosphate) to maximize brightness and go beyond what is possible in bulk optics, showing simultaneously high state fidelity, heralding efficiency, and spectral purity across three experiments: first we show record heralding efficiency in a fully-fibered heralded single-photon source, and use it to probe the tradeoff between spectral purity and heralding efficiency in non-engineered sources. With an engineered source, we then herald up to 50 photons in a nonclassical state. The last source is for polarization-entangled photon pairs, with brightness of 3.5 million pairs/s·mW, fidelity to a Bell state of 96%, heralding efficiency of 43%, and HOM interference visibility of 82%. Once a complex state is constructed, it must also be verified. For this we employ a time-multiplexed detector consisting of a fibre loop and a single-photon detector. Surprisingly, we are able to extract information even in the saturation regime of the detector. We use the click statistics of the time-multiplexed detector to verify the non-classicality of quantum light, and we use its extremely high dynamic range (123 dB) to measure a macroscopic power level with a single-photon detector. Eliminating calibrated attenuators with this approach will allow direct standardization of quantum and classical optical power levels.

High power polarised narrow linewidth sources are of immense importance in coherent beam combining (increased path length accuracy), spectral beam combining (reduced angular spread), non-linear frequency conversion (increased parametric gain) and remote detection. Power scaling of narrow linewidth sources is primarily limited by Stimulated Brillouin Scattering which can be overcome by spectral broadening before amplification to higher powers. Various applications have different requirements of spectral purity and power which can be met if the source line width is tunable. We demonstrate a narrow line width polarisation maintaining (PM) laser with continuous linewidth tuning from ~2.88 GHz to ~9.88 GHz with over 20 W of output power with a polarisation extinction ratio (PER) greater than 20 dB. We achieve continuous linewidth tuning through pure phase modulation of a 1064 nm DBR laser with a white noise source whose bandwidth and power are tuned with a low pass filter bank and variable attenuation of the drive voltage to the modulator. This dual control mechanism enables gapless tuning of the linewidth of the source. A cascade of optimized PM Yb-doped fiber preamplifier and power amplifier is used to scale the output power to over 20W. Combined with the wavelength tuning of the DBR seed, the tunable spectral width makes it versatile for use in a wide range of applications.

Cascaded Raman fiber lasers is the only proven technology which enables high power continuous wave (CW) fiber laser sources outside rare-earth emission bandwidths. Among these systems, recently demonstrated cascaded Raman fiber lasers based on Random distributed feedback (RDFB) provide wavelength agility enabling high-power, ultra-broad band wavelength tunable fiber lasers. However, these systems are limited in terms of power scaling due to degrading spectral purity with increasing input pump power which in turn limits the applicability of these systems. This is due to conversion of desired wavelength into next higher order Raman stokes with increase in pump power. In this work, we demonstrate a high power, ultra-high spectral purity, broadly wavelength tunable cascaded Raman fiber laser. This was enabled by culmination of two significant advances over the last year. To terminate the Raman cascade at the required output wavelength, we utilized our recently proposed distributed filtered feedback mechanism. To achieve high spectral purity, we used a recently demonstrated technique of using high power fiber based Amplified Spontaneous emission (ASE) sources as the input pump. A maximum output power of ~33W at 1.5μm and ~27W at 1.4μm was achieved. High spectral purity of

Dispersion induced power penalty limits the applicability of Double SideBand with Carrier (DSB+C) signals in Radio-over-Fiber type of communication system. The issue is alleviated using Single Sideband with Carrier (SSB+C) modulated signals where either upper or lower order sidebands are retained while suppressing the others. In this work, we propose a fully integrated and configurable solution to suppress one sideband using Micro Ring Modulator (MRM) and a Self-Coupled Micro Ring Resonator (SCMRR) on Silicon. A DSB+C signal is generated by MRM, and the sideband is suppressed using SCMRR. SCMRR works on splitting of cavity resonance by exciting counter-propagating mode in a controlled manner. The split notches are then utilized for selecting the carrier and one sideband. Using the proposed method, we demonstrate generation of SSB+C signal with a bandwidth of 55GHz and an Optical Sideband Suppression Ratio (OSSR) of 56dB. The solutions offer complete reconfigurability of OSSR via thermo-optic tuning and of bandwidth by varying the resonance split. At 15GHz, we report OSSR tunability of 25dB (15db-38dB) using a Peltier heater and bandwidth of 55GHz and 10GHz by engineering the optical power in the counter-propagating mode. Phase noise and polarization parameter measurements of the down-converted RF signal is performed to assess the spectral purity and polarization dependent variations. We also report bit error rate and eye diagram analysis of our device at 12.5Gbps which is only limited by the capability of the instruments involved.

This paper reports a DBR High Power Diode Laser (DBR-HPDL) realization, emitting up to 14W CW in the 920nm range. Key feature is the use of a multiple-order Electron Beam Lithography (EBL) optical confining grating, stabilizing on same wafer multiple wavelengths by a manufacturable and reliable technology. In present paper, on the same wafer, three pitches DBR-HPDLs 2.5nm spaced have been demonstrated with excellent characteristics of power, spectral purity and stability. Moreover, excellent uniformity of performances across the wafer with different emitted wavelengths demonstrates the maturity of proposed technology for high yield, high volume laser diode production for wavelength stabilized applications.

Laser diodes based on Gallium Nitride (GaN) are useful devices in a wide range of applications including atomic spectroscopy, data storage and optical communications. To fully exploit some of these application areas there is a need for a GaN laser diode with high spectral purity, e.g. in atomic clocks, where a narrow linewidth blue laser source can be used to target the atomic cooling transition. We report on the continuous wave, room temperature operation of a distributed feedback laser diode (DFB-LD) with high-order notched gratings. The design, fabrication and characterization of DFB devices based on the (Al,In) GaN material system is described. A single peak emission at 408.6 nm with an optical power of 20 mW at 225 mA and a side mode suppression ratio (SMSR) of 35 dB was achieved. Additionally, we demonstrate the use of a GaN DFB-LD as a transmitter in visible optical communications system. We also present results from a DFB-LD optimized for laser cooling of Sr+.

Extreme ultraviolet (EUV) lithography is the most promising candidate for sub-1x nm pattering. CO2 laser irradiates to a Sn droplet and then, EUV radiation can be emitted. In this process, infrared radiation (IR) is simultaneously emitted 3 to 5 times more than EUV radiation. In order to suppress IR, spectral purity filter (SPF) [8] at collector mirror and dynamic gas lock (DGL) [4] are used. Nevertheless, some amount of IR still reaches to the wafer and it can lead to wafer heating issue, so that we investigated temperature and deformation of the wafer by using finite element method (FEM) simulation. Two different silicon wafer types are compared. There is a difference in temperature and deformation between single layered wafer with and without the bottom chuck. We also found that the temperature increased more with added stacks like hard mask or photoresist on the top of the wafer.

In imaging detection of Lyman-a line of solar spectrum, in order to maintain spectral purity, a narrowband 121.6 nm minus filter is in urgent demand. Here, first-, second-, third-order narrowband 121.6 nm minus filters are designed, fabricated, and test. We just give our initial results, and due to complexity in characterization of optical constants in 115-130 nm, there are still significant deviations between design and experimental results.

High resolution gas spectroscopy in the mid-infrared in a transportable device is a big challenge allowing to address numerous applications: air quality or industrial process monitoring, defense and security, medical diagnostics... Together with high tunability in the mid-infrared, spectral purity, narrow bandwidth, compactness and robustness are needed. Nested Cavity doubly resonant OPO (NesCOPO) fulfill all those requirements. This architecture is already commercialized (in the X-FLR8 portable gas analyzer from Blue Industry and Science) and allows to reach low threshold compatible with the use of compact micro-chip nanosecond YAG laser. A wide spectral range can be obtain (2 - 10 μm). In the most mature version NesCOPO takes benefit of down-conversion of a laser radiation at 1.064 μm in a PPLN bulk crystal and give rise to two secondary radiation around 1.5 μm and between 3.2 and 4.25 μm. This last radiation is used to probe rovibrational absorption lines of species of interest using absorption or transmission spectroscopy. Speed in the selection of the emitted wavelength can be an important requirement especially when security is involved. We use engineering of the crystal using fan-out configuration. Evolution of the bandwidth and phase shift between the three waves after reflection onto the end cavity mirror has to be managed to maintain high conversion efficiency. Experiment show more flexible behavior than expected with theory. This lead to fine wavelength control on the overall emission spectrum (over 1 μm) without using crystal temperature tuning that slow down tuning speed.

Cascaded Raman lasers enable high powers at various wavelength bands inaccessible with conventional fiber lasers. However, the input and output wavelengths are fixed by the multitude of fiber gratings in the system providing feedback. In this work, we demonstrate a high power, tunable, grating-free cascaded Raman fiber laser with an output power of >30W and a continuous tuning range from 1440nm to 1520nm. This corresponds to the entire in-band pumping region of Erbium doped gain media. Our system is enabled by three novel aspects – A grating free feedback mechanism for Raman lasers, a filter fiber to terminate the Raman cascade at the required wavelength band and a tunable high-power Ytterbium doped fiber laser as input. In this work, the primary system is a novel, cascaded Raman conversion module which is completely color blind to the input pump source and does wavelength band conversion at high efficiency. In addition, the conversion module also provides high spectral purity of greater than 85% at the required wavelength by terminating the cascade using high distributed losses provided by specialty Raman filter fibers. Using a high-power Ytterbium doped fiber laser continuously tuned from 1060nm to 1100nm and Raman filter fiber with distributed loss beyond 1520nm, we achieve a continuously tunable 1440nm to 1520nm laser corresponding to 5th or 6th Raman Stokes shift of the input. To the best of our knowledge, the reported powers at these wavelengths have been the highest for tunable Raman fiber lasers and is currently only limited by the input power.

This paper reports a DBR High Power Diode Laser (DBR-HPDL) realization, emitting up to 10W in the 920 nm range. High spectral purity (90% power in about 0.5 nm), and wavelength stability versus injected current (about 5 times more than standard FP laser) candidates DBR-HPDL as a suitable device for wavelength stabilized pump source, and high brightness applications exploiting Wavelength Division Multiplexing. Key design aspect is a multiple-orders Electron Beam Lithography (EBL) optical confining grating, stabilizing on same wafer multiple wavelengths by a manufacturable and reliable technology. Present paper shows preliminary demonstration of wafer with 3 pitches, generating DBRHPDLs 2.5 nm spaced.

The distribution of high spectral purity reference signals over optical fibre in future telecommunication satellite payloads is presented. Several types of applications are considered, including the distribution of a reference frequency at 10 MHz (Ultra-Stable Reference Oscillator) as well as the distribution of a radiofrequency oscillator around 800 MHz (Master Local Oscillator). The results of both experimental and theoretical studies are reported. In order to meet phase noise requirements for the USRO distribution, the use of an optimised receiver circuit based on an optically synchronised oscillator is investigated. Finally, the optical distribution of microwave local oscillators at frequencies exceeding 20 GHz is described. Such a scheme paves the way to more advanced sub-systems involving optical frequency-mixing and optical transmission of microwave signals, with applications to multiple-beam active antennas.

Space-borne lidar systems require laser transmitters with very good performance in terms of output power, beam quality, conversion efficiency, long term reliability and environmental compatibility. Atmospheric gas sensing additionally requires spectral purity and stability.

AdvR, through support of the NASA SBIR program, has developed fiber-based components and sub-systems that are routinely used on NASA’s airborne missions, and is now developing an environmentally hardened, diode-based, locked wavelength, seed laser for future space-based high spectral resolution lidar applications. The seed laser source utilizes a fiber-coupled diode laser, a fiber-coupled, calibrated iodine reference module to provide an absolute wavelength reference, and an integrated, dual-element, nonlinear optical waveguide component for second harmonic generation, spectral formatting and wavelength locking. The diode laser operates over a range close to 1064.5 nm, provides for stabilization of the seed to the desired iodine transition and allows for a highly-efficient, fully-integrated seed source that is well-suited for use in airborne and space-based environments. A summary of component level environmental testing and spectral purity measurements with a seeded Nd:YAG laser will be presented. A direct-diode, wavelength-locked seed laser will reduce the overall size weight and power (SWaP) requirements of the laser transmitter, thus directly addressing the need for developing compact, efficient, lidar component technologies for use in airborne and space-based environments.

We have developed a packaged fiber amplifier configuration that allows for nearly two orders of magnitude of pulse width adjustment from 1ns to >800ns. This has been developed for both the 1-micron and 1.55-micron spectral regions. Our 1.55-micron fiber laser is packaged into a 6.63 x 8.65 x 3.47 in3 box, while our 1-micron fiber laser is packaged into a 13.68 x 8.68 x 3.56 in3 box, with the larger package a result of larger fiber components. These lasers offer a wide range of adjustable operating points, with total output ultimately limited by available pump power. For 1ns pulses, our 1.55-micron system generates up to 6μJ of pulse energy (>6kW peak) with transform-limited spectral output. Higher energies and output powers are achievable (up to 33μJ at 25kW peak), but the spectral output broadens slightly due to nonlinearities with 10kW peak) with high spectral purity. At >10ns pulse durations, the same laser can generate up to 40μJ pulse energy (pump limited). A unique aspect of our design is that a single fiber laser package can be electrically adjusted to produce the full range of pulse widths at repetition rates ranging from 100kHz to

We report experimental studies on Kerr optical frequency generated with a a magnesium fluoride whispering gallery-mode disk-resonator. We particularly focus on microwave generation obtained after extracting the beat-note of the comb through fast photodetection. Primary comb patterns are excited through detuning the laser frequency with regards to the cold-cavity resonance, and they provide microwaves with different frequencies and high spectral purity.

Narrow-linewidth lasers are key elements in optical metrology and spectroscopy. From their spectral purity, the measurements accuracy and the overall quality of collected data critically depend. Crystalline micro-resonators have undergone an impressive development in the last decade, opening new ways to photonics from the mm to the μm scale. Their wide transparency range and high Q-factor make them suitable for integration in compact apparatuses for precision spectroscopy from the visible to the mid-IR. Here, we present our recent results on frequency stabilization and linewidth narrowing of quantum cascade lasers using crystalline Whispering Gallery Mode Resonators for mid-IR precision spectroscopy.

Recently TNO has established EBL2; an exposure and analysis facility for testing EUV optics, reticles and pellicles under relevant EUV scanner and source conditions. The facility and EUV source complies with the ASML power roadmap of EUV systems up to a power of 500 W IF. This enables life time testing of EUV optics, reticles and pellicles under conditions which are not yet available to industry, helping the industry in preparing for HVM production. The EBL2 facility consists of a EUV source, collector optics, exposure chamber, XPS chamber, and automated sample handling. The exposure chamber has capabilities for plasma analysis, imaging ellipsometry for in-situ analysis of the sample under radiation, photodiodes for power measurements and a scintillator disk for spot profiles. It is possible to insert spectral purity filters and apertures in the beam line for wavelength tuning and beam shaping. The source is Sn fueled DPP source made by our partner Ushio and is based on the proven technology from the ASML AD-tools, providing a similar spectrum and pulse shape as used in the ASML NXE scanners. We show the results of first light obtained in December 2016. The XPS is capable of handling and analyzing full reticles and data on the obtained surface sensitivity and imaging quality will be shown.

We present experimental results on a three-section master oscillator power amplifier at 1.57 μm to be applied in an integrated path differential absorption LIDAR system for column-averaged atmospheric CO 2 measurements. The application requires high power and good beam quality together with spectral purity and modulation capacity to be used in a random modulation CW LIDAR system. The device consists of a distributed feedback laser acting as master oscillator, a bent modulator section and a tapered optical amplifier section with a tilted front facet to avoid coupled cavity effects. The modulator section acts as an absorber or amplifier when driven at zero or positive bias. Devices with different geometries and epitaxial structures were fabricated and characterized, presenting CW output powers higher than 350 mW and stable single mode emission. At the frequency required by the application (12.5 MHz) a high optical modulation amplitude and extinction ratio were achieved.

A reproducible measurement of in-band EUV power over time is essential in EUV lithography, e.g. for dose control, for monitoring the transmission of (parts of) the optical path and for detecting changes in EUV source performance. However, all currently available sensors suffer from sensitivity degradation over time due to photon-induced contamination and/or structural degradation. For instance, a growing carbon layer on a sensor surface, as may be deposited during exposure to EUV, inhibits detection of an increasingly significant fraction of the EUV power. To minimize a change of sensor response over time, TNO is developing a carbon-contamination-tolerant EUV power sensor that can operate under typical EUV vacuum conditions. The sensor uses the photo-electric effect to distinguish between in- and out-of-band EUV. The sensor concept has been tested in the EUV beam line at TNO using a Xe discharge produced plasma (DPP) EUV source. Here, we present the latest experimental results, showing the time-resolved response of the sensor to the EUV pulse. A spectral purity filter was used to compare the sensor response to the full source spectrum output and to typical Xe DPP EUV emission lines (wavelength range 10-20 nm) only. The EUV signature in the sensor signal was clearly recognizable in both cases. The normalized observed EUV pulse power reproducibility was σ/μ = 23%, reflecting the typical EUVemission power fluctuations of this Xe DPP EUV source.

In order to test the working status of adaptive optics systems, it is necessary to design a disturbance signal module. Disturbance signal module based on DDS (Direct Digital frequency Synthesis) is used to generate single-frequency disturbance signal to test the working conditions of deformable mirror and adaptive optics systems. But DDS is a periodic sampling sequence and will inevitably lead to the introduction of periodic noise which makes the disturbance signal scattering. This paper uses two methods to reduce the scattering of the single-frequency signal generated by DDS technology. The first method is the compression ROM table. In the case of the same ROM capacity, it is equivalent to extend the compressed ROM table with 256 points to ROM table with 1024 points. In this process, Oversampling is introduced to improve spectral purity to reduce the scattering of the single-frequency signal. The second method is the random phase jitter technology. It introduces m sequence as DDS sampling output random phase jitter unit. The purpose is to generate some random number added at the end of the phase accumulator. As a result, the output does not always push back than ideal, but randomly in advance, thus breaking its periodicity. This method changes the original uniform look-up sampling into a random non-uniform look-up sampling, making DDS output spectrum white. It can also improve spectral purity of the DDS output, thereby reducing the scatting of the single-frequency signal generated by DDS technology.

International audience; After a brief review of recent results achieved at Laboratoire Charles Fabry concerning high reflectivity mirrors, mirrors with enhanced spectral purity and broadband mirrors, we describe a new approach to design high efficiency multilayer mirrors for application on a broad spectral range. The main idea is to use 2 “spacer” materials (Aluminum and Scandium) in combination with a third material (Boron carbide or Silicon Carbide). We present several examples of design optimization using such multilayers. Finally, we show the first preliminary experimental results with Al/Sc/B4C and Al/Sc/SiC multilayers deposited by ion beam sputtering.

The use of a channel-cut monochromator is the most straightforward method to ensure that the two reflection surfaces maintain alignment between crystallographic planes without the need for complicated alignment mechanisms. Three basic characteristics that affect monochromator performance are: subsurface damage which contaminates spectral purity; surface roughness which reduces efficiency due to scattering; and surface figure error which imparts intensity structure and coherence distortion in the beam. Standard chemical-mechanical polishing processes and equipment are used when the diffracting surface is easily accessible, such as for single-bounce monochromators. Due to the inaccessibly of the surfaces inside a channel-cut monochromator for polishing, these optics are generally wet-etched for their final processing. This results in minimal subsurface damage, but very poor roughness and figure error. A new CMP channel polishing instrument design is presented which allows the internal diffracting surface quality of channel-cut crystals to approach that of conventional single-bounce monochromators.

Hyperspectral imaging (HSI) is being evaluated as a pre-selection tool to categorize and localize populations of microbial colonies directly onto their culture medium, in order to facilitate the microbiology workflow downstream the incubation step. The categorization criteria were here limited to the diffuse radiance spectra acquired mostly in the visible region between 400 and 900 nm. Although the diffuse radiance signal is much broader than the one acquired using vibrational techniques such as Raman and IR and limited to chromophores absorbing in the visible region, it can be acquired very quickly allowing to perform hyperspectral imaging of large objects (i.e. Petri dishes) with throughputs that are compatible with the needs of a clinical laboratory workflow. Moreover, additional cost reduction could possibly be achieved using application-specific multispectral systems. Furthermore, recent research has shown that good power of discrimination, at the species level, could be achieved at least for a low level of species. In our work, we test different culture media, with and without a strong light absorption in the visible region, and report categorization results obtained when selecting end-member spectra according to a multi-parametric study (colonies, agar type). Results of categorization (e.g. at the species level) are presented using two types of supervised-categorization algorithms providing that they deliver subpixel fractional abundance information (Linear Spectral Unmixing type) or not such as Spectral Angle Mapping (SAM) and Euclidian Distance (ED) type. Interestingly the performance between the two classes of algorithms is dramatically different, a trend which is not always observed. An interpretation is proposed on the basis of the agar interference and the spectral purity of end-member spectra.

Here we present the experimental demonstration of a Silicon ring resonator photon-pair source. The crystalline Silicon ring resonator (radius of 18.5μm) was designed to realize low dispersion across multiple resonances, which allows for operation with a high quality factor of Q~50k. In turn, the source exhibits very high brightness of >3x105 photons/s/mW2/GHz since the produced photon pairs have a very narrow bandwidth. Furthermore, the waveguidefiber coupling loss was minimized to 1900. The low coupling loss (3dB fiber-fiber) also allowed for operation with very low off-chip pump power of 20nm), which could be used in future wavelength division multiplexed quantum networks.

The combination of a 10.6 μm main pulse CO2 laser and a 1064 nm pre-pulse Nd:YAG laser in EUV source concepts for HVM would require collector mirrors with an integrated spectral purity filter that suppresses both laser wavelengths. This paper discusses a new approach of a dual-wavelength spectral purity filter to suppress 10.6 μm and 1064 nm IR radiation at the same time. The dual-wavelength spectral purity filter combines two binary phase gratings that are optimized for 10.6 μm and 1064 nm, respectively. The dual phase grating structure has been realized on spherical sub-aperture EUV collector mirrors having an outer diameter of 150 mm. IR suppression factors of 260 at 10.6 μm and 620 at 1064 nm have been measured on the sub-aperture EUV collector while its EUV reflectance exceeded 64 % at 13.5 nm.

We have realized an ultrafast diode containing a single quantum dot, whose transitions can be Stark shifted in a few hundred picoseconds. Carrying out resonant excitation of this sample we demonstrate pulsed single photon emission with high spectral purity, by rapidly sweeping the neutral exciton transition into and out of the laser energy. Detailed study of the detuning dependence of the fluorescence reveals sources of decoherence in this sample, which we show can be filtered out with narrow-band excitation.

Infrared (IR) digital holography (DH) based on CO 2 lasers has proven to be a powerful coherent imaging technique due to the reduced sensitivity to mechanical vibrations, to the increased field of view, to the high optical power and to possible vision through scattering media, such as smoke. In this contribution we report IR DH based on the combination of quantum cascade laser (QCL) sources and a high resolution microbolometric camera. QCLs combine highly desirable features for coherent imaging, such as compactness, high optical power, and spectral purity. The present availability of external cavity mounted QCLs having a broad tuning range, makes them suitable sources for multiple wavelength holographic interferometry. In addition, QCL emission covers several windows throughout a large portion of the IR spectrum, from the mid-IR to the terahertz region. This allows taking advantage of the different optical response of the imaged objects at different frequencies, which is crucial for applications such as non-destructive testing and biomedical imaging. Our holographic system is suitable for the acquisition of both transmission holograms of transparent objects and speckle holograms of scattering objects, which can be processed in real time to retrieve both amplitude and phase.

The main advantage of an optoelectronic oscillator (OEO) is the ability to synthesize directly very high spectral purity frequency in microwave domain. Beside applications in radar, telecommunication and satellite systems, OEO can also be used in sensor applications such as refractive index or distance measurements. However, the long-term stability of the OEO is easily affected by ambient environment variations. The optical fiber loop effective refractive index varies corresponding to its surrounding temperature changes. Consequently, it makes the optical transmission path inside the fiber loop differ from the initial state, leading to oscillation frequency changes. To stabilize the single loop OEO, it is essential to keep its high Q elements in a well-controlled thermal box as much as possible. Unfortunately, in the real implementation condition, this requirement is difficult to be satisfied. In this paper, we present a new technique to estimate the oscillation frequency variation under the room temperature by using a vector network analyzer (VNA). Experimental results show a good correlation between OEO oscillation frequency drift and the phase measured by the VNA. This technique can be implemented to apply corrections when using the OEO as a distance variation or a refractive index measurement tool. We also tracked the temperature of the fiber loop at the same time with the VNAbased experiment to compare two correlations of temperature and phase with OEO oscillation frequency.

We present the recent development of high performance compact THz sources based on intracavity nonlinear frequency mixing in mid-infrared quantum cascade lasers. Significant performance improvements of our THz sources in the spectral purity, frequency coverage as well as THz power are achieved by systematic optimizing the device's active region, waveguide, phase matching scheme, and chip bonding strategy. Room temperature single-mode operation in a wide THz spectral range of 1-4.6 THz is demonstrated from our Cerenkov phase-matched THz sources with dual-period DFB gratings. High THz power up to 215 μW at 3.5 THz is demonstrated via epi-down mounting of our THz device. The THz power is later scaled up to mW level by increased the mid-IR power and conversion efficiency. The rapid development renders this type of THz sources promising local oscillators for many astronomical and medical applications.

Though scaling of source power is still the biggest challenge in EUV lithography (EUVL) technology era, CD and overlay controls for transistor‟s requirement are also precondition of adopting EUVL in mass production. Two kinds of contributors are identified as risks for CDU and Overlay: Infrared (IR) and deep ultraviolet (DUV) out of band (OOB) radiations from laser produced plasma (LPP) EUV source. IR from plasma generating CO2 laser that causes optics heating and wafer overlay error is well suppressed by introducing grating on collector to diffract IR off the optical axis and is the effect has been confirmed by operation of pre-production tool (NXE3100). EUV and DUV OOB which are reflected from mask black boarder (BB) are root causes of EUV-specific CD error at the boundaries of exposed shots which would result in the problem of CDU out of spec unless sufficiently suppressed. Therefore, control of DUV OOB reflection from the mask BB is one of the key technologies that must be developed prior to EUV mass production. In this paper, quantitative assessment on the advantage and the disadvantage of potential OOB solutions will be discussed. EUV and DUV OOB impacts on wafer CDs are measured from NXE3100 & NXE3300 experiments. Significant increase of DUV OOB impact on CD from NXE3300 compared with NXE3100 is observed. There are three ways of technology being developed to suppress DUV OOB: spectral purity filter (SPF) as a scanner solution, multi-layer etching as a solution on mask, and resist top-coating as a process solution. PROs and CONs of on-scanner, on-mask, and on-resist solution for the mass production of EUV lithography will be discussed.

Single-mode lasers in the spectral region between 620 nm and 630 nm are still realized using complex laser systems, such as ring-dye laser or using non-linear frequency shifted lasers, when used in applications such as laser cooling of beryllium ions or spectroscopy on rare earth elements. Direct emitting AlGaInP based diode lasers offer a much simpler approach to this wavelength range, but so far lack a suitable beam quality and spectral purity. Recently distributed Bragg reflector (DBR) ridge waveguide lasers (RWL) were developed for the 630 nm to 640 nm region. Building on this knowledge CAMFR simulations were performed to find suitable grating periods and duty cycles to obtain emission wavelengths below 630 nm. The grating itself was then introduced by stepper lithography and reactive ion etching into the laser structure. The manufactured DBR-RWLs show laser emission at 628.5 nm and 626.5 nm at a temperature of 15°C with threshold currents below 150 mA. The spectral emission shows single-mode operation with side mode suppression ratios > 20 dB. Two DBR-RWLs with the shorter wavelength were packaged into sealed TO-3 housings to provide a small-sized non-condensing environment with temperatures down to -25°C. When cooled internally to about 0°C, an emitted power of more than 50 mW was measured at a wavelength of 626.0 nm. At this operation point a diffraction-limited single longitudinal mode was observed that allowed a heterodyne measurement where a spectral width below 1 MHz was obtained. These new diode lasers have the potential to drastically miniaturize existing set-ups for quantum information processing.

Methane is a potent greenhouse gas and on a per molecule basis has a warming influence 72 times that of carbon dioxide over a 20 year horizon. Therefore, it is important to look at near term radiative effects due to methane to develop mitigation strategies to counteract global warming trends via ground and airborne based measurements systems. These systems require the development of a time-resolved DIAL capability using a narrow-line laser source allowing observation of atmospheric methane on local, regional and global scales. In this work, a demonstrated and efficient nonlinear conversion scheme meeting the performance requirements of a deployable methane DIAL system is presented. By combining a single frequency 1064 nm pump source and a seeded KTP OPO more than 5 mJ of 1.6 μm pulse energy is generated with conversion efficiencies in excess of 20%. Even without active cavity control instrument limited linewidths (50 pm) were achieved with an estimated spectral purity of ~95%. Tunable operation over 400 pm (limited by the tuning range of the seed laser) was also demonstrated. This source demonstrated the critical needs for a methane DIAL system motivating additional development of the technology.

We present the stabilization of the beatnote of an Er,Yb:glass Dual Frequency Laser at 1.53 μm with optical fiber delay lines. Instead of standard optoelectronics oscillators, this architecture does not need RF filter and offers a wide tunability from 2.5 to 5.5 GHz. Thank to a fine analysis of the laser RIN to phase noise conversion in the photodiodes, the expected RF-amplifiers noise limit is reached with a phase noise power spectral density of -25 dBc/Hz at 10 Hz (respectively -110 dBc/Hz at 10 kHz) from the carrier over the whole tuning range. Implementation of a double fiber coil architecture improves the oscillator spectral purity: the phase noise reaches a level of -35 dBc/Hz at 10 Hz (respectively -112 dBc/Hz respectively 10 kHz) from the carrier.

We demonstrate a robust, compact, low-cost, pulsed, linearly polarized, 1064 nm, Yb:fiber laser system capable of generating ~100 kW peak power pulses and >17 W average power at repetition rates of 80 – 285 kHz. The system employs a configurable microchip seed laser that provides nanosecond (~1.0 – 1.5 ns) pulse durations. The seed pulses are amplified in an all-fiber, polarization maintaining, large mode area (LMA) fiber amplifier optimized for high peak power operation. The LMA Yb:fiber amplifier enables near diffraction limited beam quality at 100 kW peak power. The seed laser, fiber amplifier, and beam delivery optics are packaged into an air-cooled laser head of 152×330×87 mm3 with pump power provided from a separate air-cooled laser controller. Due to the high peak power, high beam quality, spectral purity, and linearly polarized nature of the output beam, the laser is readily frequency doubled to 532 nm. Average 532 nm powers up to 7 W and peak powers exceeding 40 kW have been demonstrated. Potential for scaling to higher peak and average powers in both the green and infrared (IR) will be discussed. This laser system has been field tested and demonstrated in numerous materials processing applications in both the IR and green, including scribing and marking. We discuss recent results that demonstrate success in processing a diverse array of representative industrial samples.