Laser Cavity Design Research Articles

Light on a lattice

In this paper, we shall outline some of the theoretical techniques which have been employed over the last few years in the rapidly growing field of photonic materials. Although much of the work in this area has been motivated by the photonic crystal idea, which we will discuss, the field is actually much broader than that. What we are interested in is any situation where the interaction of light with matter is sufficiently complex that Maxwell's equations cannot be solved analytically. In that case, reliable, numerical schemes are vital if we are to obtain an understanding of the physical problem at hand. The problems treated so far have been diverse ranging from novel device physics and the design of efficient laser cavities, to surface physics and the scanning near-field optical microscope and the surface enhanced Raman effect. We will consider some of these and show how the techniques we have developed can be applied to them.

Erbium–ytterbium microlasers: optical properties and lasing characteristics

In this paper we present a comprehensive review of the work done by our group on diode-pumped bulk erbium–ytterbium microlasers. Starting from an analysis of the optical properties of Er–Yb doped phosphate glasses, addressed to the modeling of the active material and to the design and optimization of laser cavities, different operating regimes and peculiar properties of these novel laser devices are described and discussed, including multi-longitudinal mode and single-frequency operation, frequency tuning and stabilization, intensity stabilization, Q-switching, mode-locking and frequency-modulation operation. Due to the high performance in terms of emission characteristics and potential low cost, these microlasers are attractive for a large number of applications and, in particular, for optical communications at 1530–1560 nm wavelengths, metrology, and telemetry at an eye-safe wavelength.

Ultrafast phenomena: A laboratory experiment for undergraduates

We present a set of experiments that introduce students to ultrafast science. We discuss the relationship between the description of an ultrashort laser pulse in the frequency domain and the time domain. Using experimental results we demonstrate that this relationship is constrained by the lower limit of the Heisenberg uncertainty principle. Students carrying out the experiments will become familiar with ultrafast techniques, such as autocorrelation and laser cavity design, as well as various other concepts such as dispersion, Fourier transformation, interference, and nonlinear optics.

Efficient, low-noise, SESAM-based femtosecond Cr 3+:LiSrAlF 6 laser

We report what we believe to be the first demonstration of a SESAM (semiconductor saturable absorber mirror)-based femtosecond Cr 3+:LiSrAlF 6 laser pumped by narrow-stripe AlGaInP laser diodes that have diffraction-limited output beams. A highly asymmetric, four-mirror laser cavity design is described for which 57 fs duration pulses at an average output power of 6.5 mW are obtained for only 72 mW of incident pump power. Pump powers of this order were maintained for over 14 h using just six 1.5 V AA batteries as the electrical power source. We have shown that mode-locking can be sustained for incident pump powers as low as 21.5 mW.

Thermal lensing measurements in line-focus end-pumped neodymium yttrium aluminium garnet using holographic lateral shearing interferometry

Thermal lensing in compact neodymium yttrium aluminium garnet slabs and rods end pumped with a beam brought to a line focus has been measured using holographic lateral shearing interferometry. This powerful technique enabled us to directly measure thermal lenses with focal lengths in the range 0.02–12 m with an accuracy of 12% and good spatial resolution. It was found that the line focused pump beam resulted in severe astigmatic thermal lensing. The measured thermal lens strongly deviated from the ideal parabolic profile along both axes, introducing an important additional consideration for laser-diode end-pumped laser resonator design. The degree of longitudinal heat flow was found to strongly influence thermal lens power. It is anticipated that results obtained from the measurement technique presented here will enable optimal design of high-power end-pumped solid-state laser cavities.

Multimode WDM optical data links with monolithically integrated multiple-channel VCSEL and photodetector arrays

We report on the design and implementation of a novel multiple-wavelength optical data link for low-cost multimode wavelength-division multiplexing (WDM) local-area network applications. This link utilizes a monolithically integrated multiple-wavelength vertical-cavity laser array and a narrow-band resonant-cavity photodetector array to transmit multiple channels of information simultaneously via a single multimode fiber. A detailed analysis on wavelength tuning and threshold characteristics of different laser cavity designs is presented. Theoretical results are compared to our experimental data. On the receiver part, both Schottky and p-i-n photodetectors with a single- or coupled-cavity structure are discussed. A novel p-i-n resonant-cavity photodetector design with a partially oxidized front mirror for linewidth control is proposed. Moreover, we also demonstrate preliminary measurements on the optical link built with our multiple-wavelength vertical-cavity laser array and photodetector array. Finally, the feasibility of constructing a multiwavelength optical data link with a single dual-core multimode fiber and an integrated laser/detector array is evaluated.

Ultralow-pump-threshold, femtosecond Cr^3+:LiSrAlF_6 laser pumped by a single narrow-stripe AlGaInP laser diode

We report what we believe to be the first demonstration of a Kerr-lens mode-locked Cr(3+):LiSrAlF(6)laser that is pumped by a single narrow-stripe AlGaInP laser diode with a diffraction-limited output beam. A novel low-loss three-mirror laser cavity design is described in which strong, localized Kerr lensing was exploited such that 75-fs-duration pulses were obtained for only 36mW of incident pump power. This pump power was maintained for 18h by just three AA batteries as the electrical power source. We have shown that mode locking can be sustained for pump powers as low as 22mW.

A modular, reconfigurable-cavity, pulsed dye laser for the advanced undergraduate laboratory

The modular pulsed dye laser described is extremely easy to build, is quickly reconfigurable into different laser cavity designs, and is usable for experiments in spectroscopy. The laser can be constructed with readily available optical components and simple hand tools. This laser is designed primarily to illustrate the performance differences of three different dye laser cavity designs: the Littrow grating (Hänsch) cavity, and both the single- and double-grating grazing incidence cavities. In the double-grating configuration, the laser’s linewidth of 0.007 nm is on the order of ten times narrower than many commercially available pulsed dye lasers. Thus the laser also has excellent performance as a spectroscopic tool. Construction, typical performance, and application details are described.

Ultra-low threshold current laser for optical parallel data communication

The drive current of a directly modulated semiconductor laser for optical parallel data communication was investigated by taking into account both the threshold current and the differential quantum efficiency which are defined from the cavity length and the mirror reflectivities. Then the drive current required for an error free data communication (bit error rate: BER<10/sup -9/) with the bit rate of 1 Gb/s was shown as a function of the threshold current with parameters of the cavity length and the mirror reflectivities. It was found that the laser cavity design which yields the minimum drive current is almost the same condition to achieve the minimum threshold current operation when the total system loss is low (<10 dB), whereas the cavity design for higher differential quantum efficiency is required when the total system loss is much higher. When the cavity length is 100 /spl mu/m and the rear mirror reflectivity R/sub r/ is 0.99 for an example, the front mirror reflectivity R/sub f/ which gives the minimum drive current was obtained to be 0.94, 0.91, and 0.8 for the total system loss of 6, 10, and 20 dB, respectively.

Low noise, all-optical gain controlled Er 3+ doped fibre amplifierusing asymmetric control laser cavity design

The authors demonstrate an Er3+ doped fibre amplifier with all-optical, automatic gain control and with near quantum limited, 1480 nm pumped noise performance. The amplifier gain is controlled by in-band laser action, and two design considerations are established for optimum noise performance: the control laser wavelength should be located in a region of high amplifier gain, and the laser cavity should be constructed to be as asymmetric as possible, ensuring minimum laser power at the signal input end of the amplifier.

Analytical design of symmetrical Kerr-lens mode-locking laser cavities

Analytical expressions for the spot size and the Kerr-lens mode-locking (LM) strength can be represented as explicit functions of the position in the cavity, the laser power, and the stability parameter for a four-mirror figure-Z laser resonator. The results indicate that the KLM strength achieves its maximum value at the edge of the stability range. Self-amplitude modulation and group-velocity dispersion compensation can be established by a prism pair. Simultaneously obtaining a large pumping efficiency and KLM is possible for this cavity.

High-efficiency diode-pumped Nd:YVO_4 slab laser

Optical-to-optical conversion efficiencies of as high as 32% with a slope efficiency of 44% were obtained with a novel diode-bar, side-pumped laser cavity design. A slab geometry with a single, high-angle-of-incidence reflection was used to extract gain from near the pump face of a Nd:YVO(4) bar that absorbed strongly at the pump wavelength. Small-signal gains of greater than 8 cm(-1) and pulse energies of as much as 3.2 mJ were obtained in an almost TEM(00) mode. Aperturing effects by the laser rod were found to limit the effects of nonuniform gain on the laser mode.

Optimizing coherent lidar performance with graded-reflectance laser resonator optics

We demonstrate how the design of graded-reflectance output coupler unstable laser cavities may be tailored to significantly enhance the overall power transmission efficiency of a given laser system relative to that of a conventional diffractively coupled unstable resonator. The importance of these findings in coherent lidar applications is explained with particular emphasis on projected space-based systems.

Analysis of the high temperature characteristics of InGaAs-AlGaAs strained quantum-well lasers

The effect of high temperature on the threshold gain and threshold current density of an In/sub 0.15/Ga/sub 0.85/As strained quantum-well laser is examined both theoretically and experimentally. It is found that the nonlinearity of the gain-versus-current relationship increases with temperature. The implications of this result on laser cavity design for optimal high-temperature performance are discussed. The effect of high temperature on modulation bandwidth is also considered. While the numerical results are specific to an In/sub 0.15/Ga/sub 0.85/As strained quantum-well laser, qualitatively they apply to all quantum-well lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Recent developments in optically pumped far-infrared lasers for plasma diagnostics (abstract)

Optically pumped far-infrared (FIR) lasers are widely utilized in the diagnosis of fusion plasmas. Applications such as interferometry, polarimetry, and collective scattering all rely heavily on the characteristics of such lasers. In particular, the stability, available power, and wavelength of the FIR laser are extremely important in establishing system performance. This describes recent development work at UCLA directed at improving the above laser characteristics. Stability improvement is investigated via the use of a FIR ring cavity which automatically eliminates the feedback effects of CO2 pump radiation. Modifications in the optical design of both CO2 and FIR laser cavities have led to increased FIR output power. Finally, the use of a novel FIR output coupler and increased pump power has increased the number of high-power FIR wavelengths available for plasma diagnostic applications. This work was supported by U.S. DOE contract No. DE-FG03-86ER-53225.

Short-pulse Q-switched 13- and 1-μm diode-pumped lasers

Acousto-optically Q-switched diode-pumped lasers emit short pulses at kilohertz repetition rates. We describe a compact laser cavity design that employs either Nd:YLF or Nd: YAG and has all internal Brewster surfaces. Pulsed operation at 1.047, 1.053, 1.064, 1.313, 1.319, and 1.338 μm is observed, with pulse widths ranging from 3 to 39 nsec at low repetition rates. The laser generates peak powers of 20 kW at 1.047 μm and 1.7 kW at 1.321 μm.

Astigmatism compensation in off-axis laser resonators with two or more coupled foci

A new method is outlined which allows the calculation of laser cavity configurations giving astigmatism compensation in complex cavities with two or more coupled foci. The method is illustrated using a hybridly mode-locked dye laser cavity design but is generally applicable to complex laser cavities.

A double-prism beam expander for pulsed dye lasers

The design of a pulsed dye laser cavity incorporating a double-prism beam expander is described and operating characteristics compared with those of single-prism systems. Narrow spectral linewidths (δλ = 0.008 Å) are achieved at relatively high efficiency (> 10%) for coumarin 500 dye solutions. Background superfluorescence in the output is low and the cavity is free from external coupling effects.

A novel double grazing-incidence single-mode dye laser

Using only one grating and plane parallel glass plate in a novel double-grazing incidence configuration, twice higher dispersion is obtained, resulting in twofold narrowing of the single-pass linewidth, compared to the single grazing-incidence scheme. This laser cavity design features several-times improved signal-to-noise ratio and enhanced stability. Single-mode operation of 210±50 MHz is demonstrated.

Frustrated Total Internal Reflection and Application of Its Principle to Laser Cavity Design

A general treatment of the phenomenon of frustrated total internal reflection is presented and numerical results are given which are related to cavity resonator design parameters. A minimum loss, minimum alignment requirement resonator is described offering a maximum of versatility. Experimental results of quasi-cw and single-pulse Q switching with a ruby optical maser are presented.