S. Naumov

Ultrabroadband infrared solid-state lasers

Ultrabroadband infrared transition metal ion-doped solid-state lasers have come of age and are increasingly being used in trace gas monitoring, remote sensing, telecommunications, ophthalmology, and neurosurgery. Operating at room temperature, they are stable, versatile, and easy to handle successors to the color center lasers. They are becoming the critical components in optical frequency standards, space-based remote sensing systems, and may soon find application in femtochemistry and attosecond science. The article reviews the principles and basic physics of these types of lasers, which are distinguished by their ability to support the shortest pulses down to single optical cycle durations and the ultimately broad tuning ranges. The paper further reviews the state of the art in the existing diode-pumped sources of broadly tunable continuous wave, and ultrashort pulsed radiation in the infrared, and provides examples of their successful application to supercontinuum generation, trace gas measurements, and ultrasensitive intracavity spectroscopy. Developments in such lasers as Cr:YAG, Cr:ZnSe, Cr:ZnS, as well as the recently proposed mixed Cr:ZnS/sub x/Se/sub 1-x/ laser, are discussed in more detail. These lasers nearly continuously cover the infrared spectral region between 1.3 and 3.1 /spl mu/m. The gain spectra of these lasers perfectly match and extend toward the infrared spectra of such established ultrabroadband lasers, operating at shorter wavelengths between /spl sim/0.7-1.3 /spl mu/m, as Ti:sapphire, Cr:LiSAF/Cr:LiSGaF and Cr:forsterite. This opens up new opportunities for synthesis of single-cycle optical pulses and frequency combs in the infrared.

DIRECTLY DIODE-PUMPED TUNABLE CONTINUOUS-WAVE ROOM-TEMPERATURE CR4+:YAG LASER

We report what is to our knowledge the first directly diode-pumped tunable (over 120 nm) continuous-wave Cr(4+): YAG laser, operating near 1.5 microm . At room temperature the laser delivered as much as 200 mW of power at 4 W of absorbed pump power. We also report observation of slow laser output degradation and bleaching in highly concentrated crystals, which we suggest is due to a photorefractive phenomenon.

Directly diode-pumped Kerr-lens mode-locked Cr^4^+:YAG laser

A directly diode-pumped Kerr-lens mode-locked Cr4+:YAG laser is demonstrated for what is to our knowledge the first time. Pulses as short as 65 fs with up to 30 mW of average output power, at a central wavelength of 1569 nm, were obtained at a repetition rate of 100 MHz. Low-loss chirped mirrors have been used for dispersion compensation up to the third order. Comparison with an Yb-fiber-pumped configuration shows good prospects for improvement.

Measuring several-cycle 1.5-µm pulses using frequency-resolved optical gating

We demonstrate frequency-resolved optical gating (FROG) for measuring the full intensity and phase of several-optical-cycle 1.5-m pulses generated from a Kerr-lens mode-locked (KLM) Cr4+:YAG laser. This involves the use of an angle-dithered second-harmonic-generation crystal to achieve the full pulse bandwidth despite the use of a relatively thick nonlinear crystal.

Mechanisms of slow bleaching in YAG:Cr4+ under cw pumping

We report on the results of lasing and spectroscopic investigations of the anomalously slow recoverable bleaching of Cr,Ca:YAG and Cr,Mg:YAG crystals. We propose two models for this effect: (i) Cr4+ reduction to Cr3+ due to oxygen valence band electron capture by Cr4+, and (ii) induced disorder in Cr4+ tetrahedral center due to effect of oxygen vacancies.

Single-shot nanosecond thermal imaging of semiconductor devices using absorption measurements

A nonscanning optical method for single-shot thermal imaging of semiconductor devices is presented. The method detects changes in the band-to-band absorption due to local self-heating effects. The device is illuminated from the substrate side and the image reflected from the device topside is detected. The illumination wavelength is set near the semiconductor absorption edge. The time resolution is 5 ns, determined by the laser pulsewidth and the space resolution is about 2 /spl mu/m. The method is applied to study the transient current distribution in electrostatic discharge (ESD) protection devices fabricated in smart power technology. The observed current spreading with time is explained in terms of a negative temperature dependence of the impact ionization coefficient. The method allows a fast analysis of the current-flow homogeneity in ESD protection and power devices.

Measurement of the excited state absorption cross-section in Cr 4+ :YAG using relaxation oscillations study

We present a measurement technique of ESA at pump wavelength for the four-level lasers. In Cr:YAG, the ESA cross-section is 2.8⋅10−18 cm2. Validity of the method is proved by comparison with the ESA-free Cr:ZnSe laser.

Pulse-measurement challenges at 1.5 microns: several-cycle pulses and several-element devices

We have demonstrated frequency-resolved optical gating (FROG) for measuring several-cycle 1.5-micron pulses using an angle-dithered-crystal geometry. We have also demonstrated experimentally a very simple GRENOUILLE device for measuring few-hundred-fs 1.5-micron pulses using the nonlinear-optical crystal Proustite.

Diode-pumped self-starting few optical cycle pulse generation at 1.5 /spl mu/m

Two ways to generate self-starting few optical cycle pulses around 1.5 /spl mu/m using a compact diode-pumped Cr:YAG laser (purely Kerr-lens mode-locking and SESAM assisted mode-locking) are reviewed. The shortest reported at 1.5 /spl mu/m transform-limited 27 fs (five optical cycles) pulses could be obtained using a novel hybrid dielectric-InGaAs/InP SESAM.

Mechanisms of the few-optical cycle pulse spectrum shift in Cr/sup 4+/:YAG laser

In this paper, we analyzed various possible causes and attribute the pulse down-frequency shift and its spectral extra-broadening in Cr/sup 4+/:YAG laser to the combined action of the intracavity third-order dispersion (TOD) and the stimulated Raman scattering (SRS) within an active medium. The results of the numerical simulations are in agreement with the experimental data obtained in the Kerr-lens mode-locked Cr/sup 4+/:YAG laser providing five optical cycle pulse generation. We showed that the pulse spectrum extra-broadening noticeably exceeding the gain bandwidth is analogous to the spectral continuum generation in fibers in the vicinity of the zero group-delay dispersion.