Microchip Solid-state Lasers Research Articles

Thermal focusing effect in solid-state microchip lasers connected directly with vertical-cavity surface-emitting laser diodes

In this paper, we model and analyze thermal focusing effect in the microchip lasers pumped by vertical-cavity surface-emitting lasers (VCSELs) for a special pump scheme, in which the microchip is axially connected with the VCSEL pump source without a gap between them to form a sort of ultra-compact monolithic micro-lasers. Thus, the thermal effects are related to twofold heating processes in the microchip. One is the common pump beam heating. The other is the heat flux diffusion from VCSEL to microchip through the contact interface between both, the latter leads to different thermo-optic characteristics from that generated only by the pump beam heating in the microchip. The temperature-, the stress- and the expansion-related phase variations and thus the thermal focusing properties of the microchip regarding the twofold heating processes are calculated and discussed for various pump power densities and temperatures of the VCSEL using analytical models. The results show that both heating processes in such a pump configuration can produce comparable thermal effects to each other. The influence of the heat transfer from the VCSEL to the microchip laser performance is discussed as well.

Chaotic oscillations associated with the breakup of polarization entangled coherent states in a microchip solid-state laser

We demonstrate the breakup of spatial-polarization entangled lasing patterns, which possess vector phase singularities, and the resultant dynamic instabilities featuring chaotic oscillations. The frequency splitting between a pair of Ince-Gauss (IG) lasing modes, originally forming a coherent entanglement state, and a self-excited additional nonorthogonal IG mode through a new class of transverse effect of self-injection pattern seeding, is shown to result in modal-interference-induced modulation at the beat frequency, leading to chaotic oscillations.

Beat note stabilization of a 10–60 GHz dual-polarization microlaser through optical down conversion

Down-conversion of a high-frequency beat note to an intermediate frequency is realized by a Mach-Zehnder intensity modulator. Optically-carried microwave signals in the 10-60 GHz range are synthesized by using a two-frequency solid-state microchip laser as a voltage-controlled oscillator inside a digital phase-locked loop. We report an in-loop relative frequency stability better than 2.5×10⁻¹¹. The principle is applicable to beat notes in the millimeter-wave range.

40-GHz Photonic Synthesizer Using a Dual-Polarization Microlaser

An optically carried microwave synthesis working at 40 GHz is demonstrated by using a two-frequency solid-state microchip laser inserted as a voltage-controlled oscillator inside a digital phase-locked loop. We report an in-loop relative frequency stability better than 2.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> . The capabilities of the synthesis are illustrated with different frequency sweeping formats.

被动调Q掺Yb3+激光材料固体微片激光器的研究进展

激光二极管抽运的被动调Q固体激光器不仅结构简单、紧凑,而且由于采用端面抽运的方式有效地耦合了抽运光和激光可以获得高光束质量的激光输出,同时由于其独特的短腔长从而可以实现亚纳秒、高峰值功率的激光输出,在激光加工、激光通信、医疗、生物和材料微结构分析等方面有非常广阔的应用前景。在过去的十多年里,采用掺镱离子（Yb3＋）的激光材料作为激光增益介质,用Cr4＋∶YAG和半导体可饱和吸收镜等作为被动调Q开关的被动调Q微片激光器取得了长足的进展,不仅获得与基于掺钕离子激光材料作为增益介质所实现的相同的高峰值功率被动调Q激光输出,而且在激光效率及激光设计的灵活性方面凸显出了明显的优点。系统地介绍了基于掺Yb3＋离子激光材料作为激光增益介质实现被动调Q微片激光器的研究进展及其在未来的发展趋势。

Magnetic Field Optical Sensor with a Laser-Diode-Pumped Microchip Solid-State Laser

A new type of magnetic field optical sensor with a diode-pumped solid-state microchip laser was studied. It was found that use of the self-mixing laser intensity modulation method combined with an acousto-optic frequency shift enabled the detection of Faraday signals in an extremely weak feedback field. Through experiments using an Nd:YVO4 microchip laser and a YIG crystal as a Faraday element, modulation signals proportional to the applied magnetic field were obtained in the very weak amplitude feedback region of 10-6.

Generation of doughnutlike vortex beam with tunable orbital angular momentum from lasers with controlled Hermite-Gaussian modes

This study demonstrates successive higher-order Hermite-Gaussian (HG(0,m)) mode operations in a microchip solid-state laser with a controlled off-axis laser diode (LD) pumping and generation of the corresponding doughnutlike laser beam of tunable ring diameter and orbital angular momentum, by experimentally focusing a Hermite-Gaussian mode (HGM) lasing beam into an astigmatic mode converter (AMC) with a mode-matching lens. Based on the successful generation of stable doughnutlike vortex beams by combining the LD off-axis pumping of microchip lasers and an AMC, this study proposes a design for a compact, solid doughnutlike vortex laser beam generator that combines three elements (i.e., laser cavity, mode-matching lens, and AMC) into one practical device. The desired doughnutlike vortex beam with different orbital angular momentum is easily generated by simply controlling the lateral off-axis pump position and pump beam shape on the laser crystal by numerical simulation.

Generation of vortex beams from lasers with controlled Hermite- and Ince-Gaussian modes

We report selective excitations of higher-order Hermite-Gaussian and Ince-Gaussian (IG) modes in a laser-diode-pumped microchip solidstate laser and controlled generation of corresponding higher-order and multiple optical vortex beams of different shapes using an astigmatic mode converter (AMC). Simply changing the pump-beam diameter, shape, and lateral off-axis position of the tight pump beam focus on the laser crystal within a microchip semispherical cavity can produce the desired optical vortex beams in a well controlled manner. Pattern changes featuring different IG and HG modes obtained by rotating the AMC are also demonstrated. Numerical simulation shows that the vortex structure is changed by controlled off-axis laser diode pumping, which could lead toward precise optical manipulation of small particles.

Blind source separation of chaotic laser signals by independent component analysis

We experimentally demonstrate blind source separation of chaos generated in Nd:YVO(4) microchip solid-state lasers by using independent component analysis. Two chaotic source signals are linearly mixed with randomly selected mixing ratio and independent component analysis is applied for the mixed signals to extract the source signals. We investigate blind source separation of many chaotic laser signals and succeed 100-signal separation of chaotic temporal waveforms. Longer temporal waveforms are required with increase of the number of mixed signals.

3D-vortex labyrinths in the near field of solid-state microchip laser

The usage of vortex-labyrinth fields and Talbot lattices as optical dipole traps for neutral atoms is considered for the wavelength of trapping radiation in the range 0.98–2.79 µm. The square vortex lattices generated in high Fresnel number solid-state microchip lasers are studied as a possible realization. The distribution of light field is obtained via a nonstationary computational model based on Maxwell–Bloch equations for a class-B laser, discrete Fox–Lee map with relaxation of inversion and a static model based on superposition of copropagating Gaussian beams. The spatial patterns obtained numerically and observed experimentally previously are interpreted as nonlinear superposition of vortices with helicoidal phase dislocations. The distribution of light field is approximated analytically by a sum of array of vortex lines and an additional parabolic subtrap. The separable optical trapping potential is proposed with similar intensity distribution. The factorization of the macroscopic wavefunction has led to the solution of the Gross–Pitaevsky equation for an ensemble of quantum particles trapped in a vortex labyrinth formed by a spatially periodic array of Laguerre–Gaussian beams.

Wavelength locking of CW and Q-switched Er^3+ microchip lasers to acetylene absorption lines using pump-power modulation

We show that modulating the diode-pump power of a microchip solid-state laser enables to lock its wavelength to a reference molecular line. The method is applied to two different types of Er,Yb:glass monolithic microchip lasers operating at 1.53 microm. First, wavelength locking of a continuous-wave dual-polarization microchip laser to acetylene absorption lines is demonstrated, without using any additional modulator, internal or external. We then show that, remarkably, this simple method is also suitable for stabilizing a passively Q-switched microchip laser. A pulsed wavelength stability of 10(-8) over 1 hour is readily observed. Applications to lidars and to microwave photonics are discussed.

Single-frequency Ince-Gaussian mode operations of laser-diode-pumped microchip solid-state lasers

Various single-frequency Ince-Gaussian mode oscillations have been achieved in laser-diode-pumped microchip solid-state lasers, including LiNdP(4)O(12) (LNP) and Nd:GdVO(4), by adjusting the azimuthal symmetry of the short laser resonator. Ince-Gaussian modes formed by astigmatic pumping have been reproduced by numerical simulation.

Chaotic dynamics and synchronization in microchip solid-state lasers with optoelectronic feedback

We experimentally observe the dynamics of a two-mode Nd:YVO4 microchip solid-state laser with optoelectronic feedback. The total laser output is detected and fed back to the injection current of the laser diode for pumping. Chaotic oscillations are observed in the microchip laser with optoelectronic self-feedback. We also observe the dynamics of two microchip lasers coupled mutually with optoelectronic link. The output of one laser is detected by a photodiode and the electronic signal converted from the laser output is sent to the pumping of the other laser. Chaotic fluctuation of the laser output is observed when the relaxation oscillation frequency is close to each other between the two microchip lasers. Synchronization of periodic wave form is also obtained when the microchip lasers have a single-longitudinal mode.

Infrared-to-green upconversion properties of Er3+/Yb3+ co-doped TeO2-TiO2-K2O glasses upon excitation with 976 nm lasers diode

The energy transfer and upconversion of Er3+/Yb3+ co-doped TeO2-TiO2-K2O glasses upon excitation with 976 nm lasers diode were studied. The tellurite glasses were prepared by conventional melting methods. Their optical properties and sensitization upconversion spectra were performed. The dependence of green upconversion luminescence intensity on the mole ratio of Yb3+ to Er3+ and Er3+ concentration were discussed in detail. When the mole ratio of Yb3+ to Er3+ is 25/1 and Er3+ concentration is 0.1% (mole fraction), or when the mole ratio of Yb3+ to Er3+ is 10/1 and Er3+ concentration is 0.15%, the optimal upconversion luminescence intensity is obtained. The obtained glasses can be one of the potential candidates for lasers-diode pumping microchip solid-state lasers.

Highly efficient pumping configuration for microchip solid-state laser

We present a new geometry for edge-pumping of a solid-state microchip laser. This design, which consists of a thin-disk gain crystal that has on top a diffusion bonded undoped material that guides the pump light, allows a good thermal heat management by reducing the thickness of the gain media, whereas the pump optics is kept simple. Simulations show that more than 0.95 of the pump radiation with uniformity coefficient in excess of 0.95 can be absorbed in an Yb:YAG/YAG composite device that has a 200-mum thick, 15-at.% Yb:YAG of 3.6-mm diameter. First experiments with this configuration produced on-time 34 W output power for 220 W on-time pump power and 0.26 slope efficiency. Power scaling possibilities are discussed.

Upconversion Properties of Er3+/Yb3+ Co-doped TeO2–TiO2–K2O Glasses

The Er3+/Yb3+ co-doped TeO2-TiO2-K2O glasses were prepared by conventional melting procedures, and their upconversion spectra were performed. The dependence of luminescence intensity on the ratio of Yb3+/Er3+ was studied, and the relationship between green upconversion luminescence intensity and Er3+ concentration is discussed in detail. The 546 nm green upconversion luminescence intensity is optimised in the studied glasses either when the Yb3+/Er3+ ratio is 25/1 and Er3+ concentration is 0.1 mol%, or when the Yb3+/Er3+ ratio is 10/1 and Er3+ concentration is 0.15 mol%. These glasses could be one of the potential candidates for LD pumping microchip solid-state lasers.

Stokes pulse energy of Q-switched lasers with intracavity Raman conversion

We derive the analytical expressions for the output Stokes pulse energy extracted from Q-switched lasers with intracavity Raman conversion. It has been shown that the problem of Stokes-pulse-energy optimization in Q-switched lasers is closely related to the optimization of intracavity photon-number density at a fundamental frequency in such lasers without the intracavity Raman conversion, although it has been found that at fixed laser parameters there is an optimum value of the cavity-mirror reflectivity at a Stokes frequency that maximizes the output Stokes pulse energy. These results have been applied for the Stokes-pulse-energy optimization of microchip solid-state lasers.

Compact Detector for Proteins Based on Two-Photon Excitation of Native Fluorescence

A compact, inexpensive detector for proteins has been constructed based on two-photon excitation of fluorescence from phenylalanine, tyrosine, and tryptophan. The fluorescence was excited by a solid-state microchip laser operating at 532 nm. Detection limits for phenylalanine, tyrosine, and tryptophan were 62 microM, 2.0 microM, and 470 nM, respectively, in a volume of 3 fL. The detection limit for a test protein, bovine serum albumin, was 130 nM.

Quantitative analysis of low-alloy steel by microchip laser induced breakdown spectroscopy

The development of a compact laser induced breakdown spectroscopy (LIBS) system increases the possibilities of applying the technique in industrial arenas, field applications and process monitoring. Significant progress has been achieved in miniaturization of optical detectors and lasers, allowing portable, low-cost LIBS equipment to be devised. Conventional lasers for LIBS, like actively Q-switched Nd:YAG lasers are limited by their bulkiness, the need for a cooling system and high power consumption. The use of a miniature solid state microchip laser overcomes these drawbacks and offers further advantages of good beam quality, high pulse repetition frequency and less damage to target. In this work we studied the quantification of elemental composition of low alloy steel samples using a higher power microchip (“powerchip”) laser. The possibility of real time, in situ quantification of such materials by powerchip LIBS enhances the applicability of the technique to process monitoring in the steelmaking industry. The performance of the LIBS technique based on a powerchip laser and a portable non-intensified, non-gated detector for elemental quantification is evaluated and compared to that obtained using an intensified detector. Calibrations were achieved for Cr, Mo, Ni, Mn and Si with linear regression coefficients between 0.98–0.99 and limits of detection below 100 ppm in most cases.

Synchronization of chaos in microchip lasers and its communication applications

We overview some experimental and numerical demonstrations on the synchronization of chaos and its communication applications using Nd:YVO 4 microchip solid-state lasers. Synchronization of chaos is achieved with several coupling configurations. Several encoding and decoding schemes for communication applications are also demonstrated by using the synchronization of chaos in microchip lasers. A new approach to secure communications using chaos based on information theoretic security is introduced. To cite this article: A. Uchida, S. Yoshimori, C. R. Physique 5 (2004).