Laser 60^th Anniversary

This month marks the 60th anniversary of the invention of the laser. Here, we highlight a few of the many developments of a technology that has revolutionised our lives. To celebrate, our editors have chosen a collection of articles published in Communications Physics that showcase the breath of research and applications in this field.

The concept of non-Hermitian parity-time reversal symmetry in optics has given rise to a vast amount of research aimed at exploring some of the exotic features displayed by photonics systems. The authors present a brief account of the state-of-the-art on non-Hermitian photonics and provide their perspective on the topic.

Formation of stable coherent structures is a fundamental physical phenomenon that occurs in various systems. This paper presents dissipative soliton build-up in mode-locked fibre lasers and investigate spectral and temporal evolution observing nonlinear dynamics ahead of the formation of a stable dissipative soliton.

Soliton explosions are a nonlinear instability phenomenon in which a dissipative soliton experiences a sudden structural collapse, but can return back to its original shape despite the strong energy dissipation. The authors report the experimental observation of soliton explosions in a fibre laser, finding that the instability is triggered by the collision of double dissipative solitons.

Optical frequency combs are important technology used in physics to distinguish between waves of different frequency. The authors have demonstrated experimentally and theoretically that quantum coherence of single photons with frequency comb characteristics can be induced by erasing which-path information of a pair of entangled photons.

The challenge of transmitting noise-free quantum optical signals needs to be overcome before they can be readily applied to quantum communication devices. The authors present a method using standard components to amplify quantum optical signals while reducing the effects of noise and maintain a high-quality, secure signal.

Optical frequency combs were realized nearly two decades ago to support the development of the world’s most precise atomic clocks, but their versatility has since made them useful instruments well beyond their original goal, and spans across a wide variety of fundamental and applied physics in a wide range of wavelengths. Fortier and Baumann present a comprehensive review of developments in optical frequency comb technology and a view to the future with these technologies.

Quantum information processing holds promise to achieve more secure data transfer in the current network of telecommunication fibres. Here, the authors review recent works implementing spatial division multiplexing in optical fibres and discuss their potential for quantum communication in classical networks.

Photoacoustic imaging of colloidal nanosystems is a useful tool for biological applications, yet current models of the photo-induced thermal processes contain un-physical assumptions. Here, the authors propose a model capable of disentangling the role of the nanoparticle, shell, surrounding material, and laser pulse properties.

Scannerless time of flight three-dimensional devices can produce high-quality images from the ground or in space and provide information on light detection and ranging. The authors design and demonstrate a downscaled subpixel 3D laser imaging device which uses pulse-encoded illumination to encode the pixels.

Acousto-optical imaging (AOI) is a technique used for deep tissue microscopy in biomedical applications. The authors use statistical approaches of super-resolution optical fluorescent imaging allowing them to realise high resolution AOI with speckle decorrelation in a much shorter time.

The development of two-dimensional (2D) layered materials is of particular importance for future electronics applications. The authors show how Confocal Laser Scanning Microscopy outperforms other characterizing techniques for wafer-scale graphene.

Diffraction experiments using high energy X-rays are used to determine molecular structures at high resolution, and with new free electron lasers diffraction experiments on non-crystalline samples are becoming achievable. The authors present a statistical method to identify hit events in flash X-ray imaging experiments of macromolecular complex and demonstrate it on RNA polymerase data.

Two dimensional materials can exhibit unique optical properties, making them interesting for new photonic devices and laser sources. Here, the strong optical nonlinearity of AuTe₂Se_4/3 is exploited to achieve a femtosecond infra-red laser with high stability.

Using semiconductor quantum dots as single-photon sources for application to quantum technologies is promising due to the high brightness and photon purity of the emitted light. Here, a method of optically switching their emission based on excitonic depletion is presented.

Femtosecond lasers are used for a vast variety of applications where super resolution is required. The authors present gain-switched semiconductor-laser operations using an extreme optical pump allowing them to generate ultrashort, high power pulses.

An optical cycling center (OCC) is a recent term describing two electronic states within a quantum object undergoing repeated optical laser excitation and spontaneous decay, while being isolated from its environment. The authors present ab-initio calculations of the ground and excited electronic and vibronic states of the polyatomic molecule SrOH providing detailed understanding of the complex molecular cooling processes with an OCC.

In high-power lasers, beams are expanded to the order of meters such to avoid damaging optical element, but increasingly large optics are impractical. Here, a diffraction grating based on laser-induced density modulations of a gas is shown to exhibit an enhanced damage threshold for nanosecond pulses.

Rapidly switching the helicity of polarised x-rays is desirable for studying magnetic dynamics via circular dichroism spectroscopy, but has not yet been realised from synchrotron radiation sources. Here, switching between ultrafast emission of monoenergetic, circularly polarized x-rays with opposite helicity is shown within a few nanoseconds.

Intense high energy laser pulses can be used on materials to produce and control features at the nanoscale, which is necessary for future generation of nanodevices. The authors report an experimental study of damage and crater formation in silicon substrates formed by focusing ultrashort extreme ultraviolet pulses from a Free Electron Laser in Japan proving a proof of concept for high control in material processing for a variety of applications.

The study of electron dynamics in relativistic laser fields is a subject of major interest within the strong field physics community and has inspired several key applications aimed at accelerating charged particles. The authors present a theoretical study, and propose an experimental design, that address the interaction of electrons with intense lasers in the transition regime from classical to quantum and show that stochastic processes in the quantum regime allow electrons to be transmitted/reflected across/by the laser in the parameter region prohibited by classical dynamics.

Laser technology is rapidly developing to the point where pulse power and intensity are expected to reach such levels that new physical processes will be able to be studied for the first time. Using simulation the authors theoretically investigate the generation of high brilliance gamma rays and electron-positron pairs during extreme intense laser interaction with a specific target.

In recent years, photonic structures that mediate the transfer of energy from a laser to a particle beam have gained interest as a way to access more compact accelerations techniques for use in a wide variety of applications. The authors investigate by numerical calculations and experimentally the effect of nonlinear pulse distortions on the operation of dielectric laser accelerators.

Ultracold atoms serve as ideal systems for precise studies of light-matter interaction. The authors report on absolute strong-field ionization probabilities of rubidium atoms exposed to femtosecond laser pulses and show that Ab-initio theory is in perfect agreement with the data at Keldysh parameters near unity.

When a material is irradiated with a high-intensity laser pulse, its surface ionization generates electrons that are accelerated close to the speed of light by the ponderomotive force of the laser light, yet how electrons’ kinetic energy scales with laser power is still unclear. The authors experimentally clarify this relation and by modelling individual electron trajectories using numerical simulations identify two acceleration mechanisms for the generation of relativistic electrons related to the dependency of the electric and magnetic fields.