The Photonics Spotlight
The Photonics Spotlight – associated with the Encyclopedia of Laser Physics and Technology – is a “blog” (web log) with the purpose of highlighting interesting news and useful information in the area of photonics, particularly laser technology and applications. The content can be related to particularly interesting scientific papers or to other forms of publications, reporting for example cute new techniques, special achievements, or useful hints.
Note that the Spotlight articles (as well as those of the Encyclopedia) are citable. Permanent links are given for each article.
This blog is operated by Dr. Rüdiger Paschotta of RP Photonics Consulting. Comments and suggestions are welcome. The news items are definitely not available for advertising, but advertisers can order banners on the right column of this page.
The new RP Photonics Buyer's Guide
Posted on 2012-08-06 as a part of the Photonics Spotlight.
Permanent link: http://www.rp-photonics.com/spotlight_2012_08_06.html
The RP Photonics website has been substantially expanded by the introduction of the new RP Photonics Buyer's Guide. This is a large database of suppliers for photonics products. Hundreds of suppliers are listed already (by name and by products), and more will follow.
Some may ask whether we need another buyer's guide, as there are several already. The answer is yes, as the RP Photonics Buyer's Guide has several unique features, providing a high value:
- It is intimately connected with the Encyclopedia of Laser Physics and Technology, which has become extremely popular. This gives the users immediate access to supplementary high-quality scientific and technical information. Readers of encyclopedia articles can move to the buyer's guide with a single click.
- The page layout is simple and clear, not excessively covered with advertising, so that the user experience will make it attractive to use this resource.
- Both for users and suppliers, it is easy to use.
For these reasons, we expect the RP Photonics Buyer's Guide to become another very popular service of RP Photonics for the worldwide photonics community.
Any so far missing suppliers are welcome to register, using a simple registration form.
The advertising opportunities have also been greatly expanded:
- Suppliers can have enhanced entries for better visibility of their companies and products.
- The banners in the right column of all encyclopedia pages are now also displayed in the buyer's guide and thus obtain a further increased value.
- Banners and company profiles can also host videos.
New Raman Lasers
Posted on 2012-03-12 as a part of the Photonics Spotlight.
Permanent link: http://www.rp-photonics.com/spotlight_2012_03_12.html
Ref.: J. Shi et al., “Highly efficient Raman distributed feedback fibre lasers”, Opt. Express 20 (5), 5082 (2012); encyclopedia article on Raman lasers; J. Lin et al., “Continuous-wave VECSEL Raman laser with tunable lime-yellow-orange output”, Opt. Express 20 (5), 5219 (2012)
Raman DFB Fiber Laser
Shi et al. (see the reference above) reported a distributed-feedback laser (DFB laser) based on stimulated Raman scattering in an optical fiber. This is quite remarkable because DFB fiber lasers have to be rather short, whereas the achievable Raman gain per centimeter is rather small. One would normally think about using some special glass with high nonlinearity, e.g., a chalcogenide or tellurite glass. The authors also suggest that, but their results were obtained with quite normal germanosilicate fibers. Their solution was to make the DFB fiber lasers relatively long – 30 cm –, but short enough for stable single-frequency operation, and to make the resonator losses fairly small with suitable fiber Bragg gratings. In that way, a reasonably low threshold pump power of 1 W or 2 W, depending on the fiber, was achieved, and the slope efficiencies were also very high: in one case 93%.
VECSEL with Intracavity Raman Conversion
The other results have been presented by J. Lin et al. (see above). Here, a continuous-wave Raman laser was realized with a vertical external-cavity surface-emitting laser (VECSEL). VECSELs are actually quite attractive for that approach, as these low-gain lasers have a high intracavity power, and compared with doped-insulator lasers, they can access different wavelength regions. The Raman shift then further expands the accessible wavelength range.
In the particular case, they even used additional sum frequency generation or frequency doubling within the resonator in order to get output wavelengths in the range 548.5–566 nm (SFG) or 577.5–596 nm (SHG). The moderate overall power conversion efficiency (a few percent) is not surprising for such a multi-step conversion scheme, and may be improved further. The output powers (up to 0.8 W at 560 nm) are already quite respectable.
Conflicting Definitions of s and p Polarization
Posted on 2012-03-03 as a part of the Photonics Spotlight.
Permanent link: http://www.rp-photonics.com/spotlight_2012_03_03.html
It is quite common to talk about s-polarized and p-polarized laser beams, incident on optical surfaces or diffraction gratings. Therefore, it is quite disturbing that there are conflicting definitions in the scientific literature:
- Usually, p-polarized light is understood to have an electric field direction parallel to the plane of incidence on a device, and s-polarized light has the electric field oriented perpendicular to that plane. (Actually, the letters have a German origin: s = senkrecht = perpendicular, p = parallel.) According to that definition, we can obtain vanishing reflectivity of a surface at Brewster's angle for p polarization. That's easy to remember: “p” is closer to “B” (like “Brewster”), so Brewster's trick works with p polarization.
- In the context of diffraction gratings, the opposite definition can be found. Here, “s” still means perpendicular, but in that case perpendicular not to the plane of incidence, but to the lines of the grating. So for s polarization, the electric field vector is perpendicular to the lines, i.e., it lies in the plane of incidence.
So there is another trap to fall into! When reading some paper, we have to find out which definition has been used.
By the way, some people call a laser beam s-polarized, when its polarization is vertical, i.e., perpendicular to the lab's floor. It is better, though, to restrict the terms s polarization and p polarization to cases where the polarization direction with respect to a plane of incidence is relevant. For example, if you have a Brewster-angled prism in the common orientation where the reflected beam stays horizontal in direction, s polarization according to the first definition above is vertical. However, if you turn the prism such that the reflected beam goes upwards, that will change, of course.
- 2012-02-03: Simulation Software: Use Commercial Products of Home-Made Software?
- 2011-12-23: Kerr-lens Mode-locked Thin-disk Laser
- 2011-06-10: Are Compact Resonators More Stable?
- 2011-05-28: Explanation for the Mode Instability in High-power Fiber Amplifiers with Few-mode Fibers
- 2011-03-13: What if Solid-State Laser Transitions Would Be Much Stronger?
- 2011-02-10: Fiber Lasers: More Difficult to Design than Bulk Lasers
- 2011-01-05: Femtosecond Fiber Amplifiers: Unlimited Peak Power?
- 2010-09-02: Why LEDs are Energy-efficient, and Why They Could Well Increase Energy Consumption
- 2010-07-27: Special SESAMs for Mode-locked High-power Lasers?
- 2010-07-12: Laser Development: Get an Expert Early on!
- 2010-06-09: Poor Man's Isolator
- 2010-05-14: Plagiarism, Exploiting the Encyclopedia of Laser Physics and Technology
- 2010-04-26: Resolution and Accuracy of Measurements
- 2010-04-16: Why Large Mode Area Waveguides Do Not Work for Laser Diodes
- 2010-04-08: Creating a Top-hat Laser Beam Focus
- 2010-03-22: All-in-one Concepts versus Modular Concepts
- 2010-03-15: Spatial Walk-off and Beam Quality in Nonlinear Frequency Conversion
- 2010-03-09: Nonlinearities in Fiber Amplifier Modeling
- 2010-03-03: Thresholds for Nonlinear Effects in Fiber Amplifiers
- 2010-02-26: New Scientific Paper: Timing Jitter and Phase Noise of Mode-locked Fiber Lasers
- 2010-02-06: Scientific Conferences and Publications: Emphasize Device Performance or Insight?
- 2010-01-29: Far From Maturity: The Photonics Industry
- 2010-01-22: Pumping Fiber Lasers with Fiber Lasers
- 2010-01-11: Beams of Laser Pointers: Visible in Air?
- 2009-12-31: Tilt Tuning of Etalons
- 2009-12-13: Johnson–Nyquist Noise in Photodiode Circuits
- 2009-12-08: Increased Output Power of a Laser with Forced Tuning
- 2009-11-22: The Beam Focus – Not Just a Demagnified Version of Your Beam
- 2009-11-18: Articles and a Quiz on Photonics Issues
- 2009-11-13: Photodetection: Optical and Electrical Powers
- 2009-11-03: Coherent Light from a Bulb?
- 2009-10-19: Risk Factors for Science Fraud and the Scientist's Responsibility
- 2009-10-12: Cold Light from the Hottest Bodies and from Cool Devices
- 2009-10-08: Nobel Prize for Charles K. Kao for Pioneering Work on Optical Fibers
- 2009-10-03: Peak Intensity of Gaussian Beam
- 2009-09-27: Lasers with Short Upper-state Lifetime
- 2009-09-19: Are Laser Resonators Power Scalable?
- 2009-09-07: Anniversary: 5 Years of the Encyclopedia of Laser Physics and Technology
- 2009-09-01: Fresnel Reflections from Double Interfaces
- 2009-08-22: Jitter and Phase Noise of Mode-locked Fiber Lasers
- 2009-08-14: Progress on Green Laser Diodes
- 2009-08-12: What is an Optical Transistor?
- 2009-07-29: No Beat Note for Orthogonal Modes
- 2009-07-23: Submit Photographs for the Encyclopedia of Laser Physics and Technology
- 2009-07-21: Signal-to-Noise Ratio and Measurement Bandwidth
- 2009-07-09: Gain-guiding Index-antiguiding Fibers
- 2009-06-29: Doing Things Properly: It's the Economy, Stupid!
- 2009-06-23: Coherence – a Black-or-White Issue?
- 2009-06-08: Prizes of the European Physical Society
- 2009-06-02: 5 Years of RP Photonics Consulting
- 2009-05-22: Interference Effects with Imbalanced Intensity Levels
- 2009-05-13: The Minimum Time–Bandwidth Product
- 2009-04-28: SPIE Field Guides
- 2009-04-19: Last Chance to Get the Encyclopedia of Laser Physics and Technology Cheaper
- 2009-04-17: Miniature Laser Projectors – The Next Big Laser Thing?
- 2009-04-06: Laser Pointers in Soccer Games: Not Necessarily Harmless
- 2009-04-05: Stability of Resonators – an Ambiguous Term
- 2009-03-19: Scientific Progress: not as Straight a Process as it Seems
- 2009-03-07: Complicated Pulse Shapes from Q-switched Fiber Lasers
- 2009-03-02: User Interfaces for Simulation Software
- 2009-02-13: Laser Beam Deflections: The Angle–Diameter Product
- 2009-01-12: Chaotic Lasing Generates Random Numbers
- 2009-01-05: Extremely Long Mode-locked Fiber Laser
- 2008-12-16: Why Fiber Amplifiers, not Fiber Lasers?
- 2008-11-25: The Gouy Phase Shift Speeds up Light
- 2008-11-08: Validating Numerical Simulation Software
- 2008-10-20: Rate Equations – An Example for Stiff Sets of Differential Equations
- 2008-10-03: Wavelength-Tunable Lasers: Does the Tuner Degrade the Power Efficiency?
- 2008-09-24: Decoupling Pulse Duration and Pulse Energy
- 2008-09-10: Unpolarized Single-Frequency Output
- 2008-08-28: Photographs for the Encyclopedia of Laser Physics and Technology
- 2008-08-15: Print Version of the Encyclopedia of Laser Physics and Technology
- 2008-07-26: Beat Signals with Zero Linewidth
- 2008-07-13: The Simplified History of the Michelson–Morley Experiment
- 2008-07-02: Stronger Focusing Avoids SESAM Damage
- 2008-06-20: All-in-One Ultrafast Laser Systems
- 2008-06-13: Heisenberg's Uncertainty Principle and the Transform Limit
- 2008-06-06: Fiber Lasers Which Are No Fiber Lasers
- 2008-05-25: Einstein and the Laser
- 2008-05-13: Easier Self-Starting Passive Mode Locking for Short Lasers
- 2008-05-05: Length of a Photon
- 2008-04-28: Different Kinds of Polarization
- 2008-04-22: Abused Photonics Terms: Coherence
- 2008-04-15: Abused Photonics Terms: Modes
- 2008-04-02: Solitons: Lower Dispersion, Stronger Dispersive Effects!
- 2008-03-26: Mode-Locked Lasers: Lower Average Powers in Shorter Pulses
- 2008-03-17: Ultrafast Fiber Lasers: Re-Inventing Mode Locking
- 2008-03-10: Automatic Phase Matching
- 2008-03-04: What is a “High” Laser Beam Quality?
- 2008-02-22: Launching Light from a Bulb into a Single-Mode Fiber
- 2008-02-14: How Laser Development Can Go Wrong
- 2008-02-12: Factor 2 in the Equation for Cross-Phase Modulation
- 2008-02-03: Quantifying the Chirp of Ultrashort Pulses
- 2008-01-27: Beam Quality in Second-Harmonic Generation
- 2008-01-14: Frequency Doubling: Long Pulses Cause Trouble
- 2008-01-06: Saturation Intensity or Saturation Fluence of a Saturable Absorber or a Laser Gain Medium: What Matters?
- 2007-12-18: The Role of Laser Safety Goggles
- 2007-12-11: The Idler Wave - Essential for Parametric Amplification and Oscillation
- 2007-12-03: New Paper on Power Scaling of Lasers
- 2007-11-26: Solving Laser Problems Step by Step
- 2007-11-19: Walk-Off and Phase-Matching Bandwidth in Nonlinear Crystals
- 2007-11-10: Retirement of Prof. David C. Hanna
- 2007-11-02: Ultrafast Laser Kills Viruses
- 2007-10-31: Thermal Equilibrium in Laser Crystals
- 2007-10-25: The Gain Bandwidth of Laser Crystals and Glasses
- 2007-10-17: Why the Second-Harmonic Beam is Smaller
- 2007-10-11: Understanding Fourier Spectra
- 2007-10-07: Effective Refractive Index: Correcting a Common Belief
- 2007-09-27: Light Plus Light = Darkness: No Energy Problem, but Quantum Weirdness
- 2007-09-21: Optimum Crystal Length for Frequency Doubling
- 2007-09-13: Using Figures of the Encyclopedia in Your Publications, and Citing the Encyclopedia
- 2007-09-07: Power Scaling in Downward Direction
- 2007-09-01: Stimulated Brillouin Scattering: Lower Peak Power, Stronger Effect?
- 2007-08-27: Distant Healing of Lasers
- 2007-08-23: An OPO Without Resonator Mirrors
- 2007-08-22: Saturation of Pump Absorption - An Important Issue?
- 2007-08-15: Light = Electromagnetic Waves?
- 2007-08-06: Fiber Amplifiers: More ASE for Larger Core with Higher NA?
- 2007-07-30: Fiber Amplifiers: Stronger ASE in Backward Direction
- 2007-07-25: Higher Heat Generation Density, Stronger Thermal Effects?
- 2007-07-16: Mode Competition - Increased or Decreased by Spatial Hole Burning?
- 2007-07-11: What is a Beam Width, Beam Size, and a Beam Waist?
- 2007-07-06: Promoting Dangerous Practices in Laser Labs
- 2007-07-01: Nonsensical Regulations Undermine Laser Safety
- 2007-06-24: The Plague of a Narrow Emission Linewidth
- 2007-06-11: Beam Quality Measurements Can Easily Go Wrong
- 2007-06-01: Characterize Your Pump Beam!
- 2007-05-26: Optical Isotropy: Nonlinear Interactions are Different!
- 2007-05-19: Why Strong Birefringence in Fibers Helps
- 2007-05-10: Fundamental Limitation for sigma-tau Product, Gain Efficiency, and Laser Threshold
- 2007-04-28: Easier Launching into Fibers with Large Mode Area?
- 2007-04-16: Questions and Answers on Shot Noise
- 2007-04-01: The Ideal Pump Intensity Distribution in an End-Pumped Solid-State Laser
- 2007-03-23: Explaining the Nature of Photons to Lay Persons
- 2007-03-16: Time To Market and the Economics of Laser Development - or How to Cause Great Financial Damage without Spending Money
- 2007-03-11: Divided-Pulse Amplification
- 2007-03-09: The Trouble with Crystal and Coating Damage
- 2007-03-05: More Efficient Frequency Doubling with Shorter Pulses?
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- 2007-02-22: Lossy Laser Cavities
- 2007-02-16: The Science of Biophotons
- 2007-02-09: Papers Reporting Yet Another Laser Crystal
- 2007-02-04: Continuing Struggle for Larger Fiber Mode Areas
- 2007-01-27: Noise Figure of Amplifiers
- 2007-01-21: Operation Far Above Threshold
- 2007-01-15: Origins of Heating in Laser Crystals
- 2007-01-09: The Myth of Fiber-Optic Polar Bears
- 2007-01-05: Why the Encyclopedia of Laser Physics and Technology is Successful
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- 2006-12-16: Dangerous Green Laser Pointers
- 2006-12-09: The Laser Industry - High Tech or Low Tech?
- 2006-12-03: Diffraction in Optical Fibers
- 2006-11-28: The Role of Diffraction in Optical Resonators
- 2006-11-21: The Resonator Mystery
- 2006-11-16: Laser Models - not Always Useful
- 2006-11-04: Nd:YVO4 Laser with Polarization-Independent Pump Absorption
- 2006-11-02: Reflection Spectrum of Tilted Dielectric Mirrors
- 2006-10-26: Residual Transmission Through Highly Reflecting Mirrors
- 2006-10-22: Lasers Attract Dust to Cavity Mirrors
- 2006-10-17: A Cute New Imaging Technique Named Compressive Imaging
- 2006-10-16: Using a Current Amplifier for Optical Power Measurements and Recording with a Photodiode
- 2006-10-15: Fivehundred Articles in the Encyclopedia of Laser Physics and Technology
- 2006-10-09: Correct Specifications for Laser Noise - Valuable but Hard to Obtain
- 2006-10-04: Higher-Order Modes of Fibers: a Solution for Single-Mode Guidance with Large Mode Area?
- 2006-10-01: Stability Zones of Laser Resonators
- 2006-09-29: Frequency Dependence of the Conversion Efficiency for Frequency Doubling
- 2006-09-22: Coherence Length of Ultrashort Pulses
- 2006-09-21: Power Scaling Limits of Optical Parametric Amplifiers
- 2006-09-16: Q-switched Lasers: YAG versus Vanadate
- 2006-09-06: Quenching Degrades the Efficiency of Some Ytterbium-Doped Gain Media
- 2006-09-03: Single-Frequency Operation Stabilized by Spatial Hole Burning
- 2006-09-03: Resolution of Conundrum: Threshold Power for Parametric Nonlinear Interactions
- 2006-09-01: Test Yourself with the Photonics Quiz
- 2006-08-23: Lasers with Nonlinear Input-Output Characteristics
- 2006-08-20: Lower Noise from Longer Lasers
- 2006-08-18: Resolution of Conundrum: No Magnetic Field on the Axis of a Coil
- 2006-08-15: The Effect of a Double Pass in a Frequency Doubler
- 2006-08-12: Understanding Quasi-Three-Level Lasers
- 2006-08-10: Single-Mode Fibers with Large Mode Areas
- 2006-08-01: Lasers Disturbed by Vacuum?
- 2006-07-30: Threshold Power for Parametric Nonlinear Interactions
- 2006-07-24: Beam Distortions in Laser Cavities
- 2006-07-23: Single-Atom Lasers
- 2006-07-22: No Magnetic Field on the Axis of a Coil?
- 2006-07-21: Photonics and Laser Technology Blogs – Where Are They?
- 2006-07-16: Spontaneous Emission and Amplifier Noise
- 2006-07-14: Lasers Like it Cool
- 2006-07-10: Strength of Thermal Lensing Effects
- 2006-07-05: Laser Design: Side Product or the Basis of Laser Development?
- 2006-07-01: Lifting the Confusion Concerning Doping Concentrations
- 2006-07-01: Characterizing a Cavity with a Frequency Comb
- 2006-07-01: With Wavelength Combs to Picometer Resolution
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