Recent advances in solid state lasers and nonlinear optics for remote sensing

Abstract

We report on several developments in solid state lasers and nonlinear optics specifically for applications in remote sensing. In the area of UV sources for ozone monitoring, we have developed an efficient, third-harmonic, tunable Ti:sapphire-laser-based source. For long-range, eyesafe detection of aerosols, we report a high-energy optical parametric oscillator (OPO) driven by a flashlamp-pumped, Q-switched Nd:YLF laser. Finally, for mid-infrared DIAL, we have developed a Tandem-OPO that converts a common Nd-doped laser into a tunable source capable of providing wavelengths in the range 1500-5500 nm and 8000-12000 nm. OZONE LIDAR SOURCEAtmospheric studies of ozone have been conducted successfully from both ground-based and aircraft-based systems employing a variety of sources that emit in the 285-to 315-nm region. The sources used to date for ozone DIAL work have included Nd:YAG-pumped, frequency-doubled dye lasers; Raman-shifted, quadrupled, Nd:YAG lasers; excimer lasers; and Raman-shifted excimer lasers. Existing aircraft and future space-based ozone measurements would benefit from coherent sources that are more efficient, compact, robust, reliable, and low-maintenance than those currently available.We describe here an all-solid-state laser transmitter, based on third-harmonic generation (THG) of a titanium-sapphire laser, that provides 35 mJ output pulses with 500-µs temporal separation in the 307-320 nm wavelength range. Ti:sapphire laserAs the tunable oscillator, we used an unstable-resonator, high-energy, gain-switched Ti:sapphire laser [1]. The laser was pumped by a high-energy, flashlamp-pumped, Q-switched, frequency-doubled, Nd:YLF laser configured for a 5-Hz, double-pulsed format. We achieved dual-wavelength operation of the Ti:sapphire laser by incorporating a mirror mounted on a high-speed galvanometer scanner that can rapidly switch the laser to any wavelength in the 920-960-nm range in a time less than the double-pulse separation of 500 µs.In order to reduce the Ti:sapphire laser linewidth and increase harmonic conversion efficiency [2] we injection-seeded the laser using two external-grating diode lasers (EOSI, Inc) tuned to regions around 925 nm and 945 nm, respectively. The linewidth of the Ti:sapphire laser was ~ 3-4 cm -1 in unseeded regime, and less than 0.007 cm -1 in seeded regime of operation.The main parameters of the pump Nd:YLF laser and unseeded Ti:sapphire tunable oscillator are given in Table 1. (When the Ti:sapphire laser was seeded the output energies were ~10-15% smaller).

Ultraviolet upconversion luminescence enhancement in Yb3+/Er3+-codoped Y2O3 nanocrystals induced by tridoping with Li+ ions

“…At present, the nonlinear sum frequency technique has usually been used to realize lasing in the UV range. However, this technique was stringently limited by the problems of rigorous phase matching, low efficiency and growth of appropriate nonlinear crystals [3]. Else, stokes-pumped UV laser has been challenged due to the lack of the short-wavelength pumping diode lasers.…”

A 243mJ, Eye-Safe, Injection-Seeded, KTA Ring-Cavity Optical Parametric Oscillator

“…The choice for the traveling cavity was based on eliminating the need for an optical isolator for the pump beam, lower energy fluences on the crystals which prevent crystal damage, and the ease of injection seeding. From Rines' and Webb's results, Qpeak developed a compact LIDAR transmitter based on a traveling wave, two crystal, NCPM KTP which was pumped by a multi-mode Nd:YLF running at 20Hz [3]. Qpeak successfully produced 210mJ of 1551nm light with a conversion efficiency of 36% [3].…”

“…From Rines' and Webb's results, Qpeak developed a compact LIDAR transmitter based on a traveling wave, two crystal, NCPM KTP which was pumped by a multi-mode Nd:YLF running at 20Hz [3]. Qpeak successfully produced 210mJ of 1551nm light with a conversion efficiency of 36% [3]. In 2007, Gong et al demonstrated an eye-safe compact scanning LIDAR based on an OPO source that generated 125mJ [4].…”

Optical parametric generation in biaxial KTA crystal under pumping by YAG:Nd laser in arbitrary directions

“…Данные о перестроечных кривых и нелинейных коэффициентах проанализированы только для случаев параметрической генерации света в главных плоскостях оптической индикатрисы кристалла KTA -XZ и YZ [1][2][3][4]. Это объясняется тем, что кристаллы KTA с вырезкой, которая обеспечивает коллинеарное трехчастотное взаимодействие в главных плоскостях оптической индикатрисы, традиционно используются для построения либо безопасных для глаз ПГС [3], либо перестраиваемых ПГС, применяемых для накачки последующих ПГС на кристаллах ZnGeP 2 и CdSe и обеспечивающих генерацию перестраиваемого излучения в средней ИК-области спектра (3-11 мкм) [5,6]. В то же время информация о перестроечных кривых и нелинейных коэффициентах при произвольных направлениях трехчастотного взаимодействия в кристалле KTA весьма актуальна и крайне необходима, поскольку достаточно широкий диапазон спектральной прозрачности KTA (0,35-5,3 мкм на «0» уровне пропускания [7]) указывает на потенциальную возможность создания с помощью кристаллов KTA ПГС, способных генерировать излучение в коротковолновой области среднего ИК-диапазона спектра (l ~ 2-5 мкм).…”