Low-cost, broadly tunable (375-433 nm & 746-887 nm) Cr:LiCAF laser pumped by one single-spatial-mode diode

Challenges in power scaling of Cr:LiCAF lasers: effect of passive losses

In this work, we have investigated the continuous-wave (cw) lasing potential of thin slab-shaped Cr:LiCAF crystals with a low chromium doping level of around 1% and various lengths of 1 to 2 cm. These relatively long crystals with low Cr-doping facilitate the distribution of heat load in a larger volume and could enable power scaling of Cr:LiCAF lasers. However, long crystals tend to have larger passive losses, and it is also more challenging to achieve efficient mode-matching to the low-brightness pump mode in a longer gain element, which could hinder laser performance. To explore the issue, we have performed detailed cw lasing experiments in single- and multimode diode-pumped Cr:LiCAF laser systems employing crystals with different doping and length. Our results showed that current state-of-the-art crystal growth methods provide Cr:LiCAF crystals with low enough passive losses to enable cw laser efficiencies of up to 50%, even in these long samples. The pump powers available in this study (5.35 W) limited the cw powers we could achieve experimentally to 2.25 W level; however, our simulations indicate that thin slab-type Cr:LiCAF crystals with low Cr-doping have the potential to achieve cw powers above 10 W level.

Broadly tunable two-color lasing of Cr:LiCAF with on-surface and off-surface optical axis birefringent filters: performance comparison

We studied the two-color lasing performance of a Cr:LiCAF laser using crystal quartz on-surface and off-surface optical axis birefringent filters (BRFs). Four different on-surface optical axis BRFs with thicknesses of 2 mm, 4 mm, 8 mm, and 16 mm, and three different off-surface optical axis BRFs with a diving angle of 25° and thicknesses of 2 mm, 4 mm, and 8 mm have been tested. Two-color lasing operation could be achieved in tens of different pairs of wavelengths using both types of BRFs. Regular on-surface optical axis BRFs provided two-color lasing in the 772-810 nm interval, with a discretely tunable wavelength separation of 1 to 37 nm (0.5 to 17 THz). In comparison, the off-surface optical axis BRFs enabled scanning of two-color lasing spectra in a much broader wavelength range between 745 nm and 850 nm with a discretely tunable wavelength separation of 0.8 to 99 nm (0.4 to 46 THz). The results clearly demonstrate the advantages of using off-surface optical axis BRFs to achieve two-color lasing with broadly tunable wavelength separation.

Standoff Chemical Detection Using Laser Absorption Spectroscopy: A Review

Remote chemical detection in the atmosphere or some specific space has always been of great interest in many applications for environmental protection and safety. Laser absorption spectroscopy (LAS) is a highly desirable technology, benefiting from high measurement sensitivity, improved spectral selectivity or resolution, fast response and capability of good spatial resolution, multi-species and standoff detection with a non-cooperative target. Numerous LAS-based standoff detection techniques have seen rapid development recently and are reviewed herein, including differential absorption LiDAR, tunable laser absorption spectroscopy, laser photoacoustic spectroscopy, dual comb spectroscopy, laser heterodyne radiometry and active coherent laser absorption spectroscopy. An update of the current status of these various methods is presented, covering their principles, system compositions, features, developments and applications for standoff chemical detection over the last decade. In addition, a performance comparison together with the challenges and opportunities analysis is presented that describes the broad LAS-based techniques within the framework of remote sensing research and their directions of development for meeting potential practical use.

3 GHz, Yb-fiber laser-based, few-cycle ultrafast source at the Ti:sapphire laser wavelength

We demonstrate a compact ultrafast source centered at 850 nm with >200 nm bandwidth (full width at half-maximum) based on a 3 GHz Yb-fiber master-oscillator-power-amplifier system. The output pulses (with up to 13 W average power) from the laser system are coupled into short (<50 mm) pieces of photonic crystal fibers to excite broadband fiber-optic Cherenkov radiation; the resulting broad phase-matching bandwidth due to short fiber length produces an upconverted spectrum spanning in the wavelength range of 750-950 nm with average power of 94, 184, and 380 mW for fiber length of 28, 37, and 48 mm, respectively. The spectrum generated from the 37 mm fiber is then dechirped by eight double-chirped mirrors, leading to compressed pulses ~14 fs in duration. Such an ultrafast source is a promising substitute of multigigahertz mode-locked Ti:sapphire lasers for applications in optical frequency metrology and multiphoton coherent microscopy.

Parametric four-wave mixing using a single cw laser

Four-wave mixing can be used to generate coherent output beams, with frequencies difficult to acquire in commercial lasers. Here, a single narrow external cavity diode laser locked to the two photon 5s-5d transition in rubidium is combined with a tapered amplifier system to produce a high power cw beam at 778 nm and used to generate coherent light at 420 nm through parametric four-wave mixing. This process is analyzed in terms of the intensity and frequency of the incoming beam as well as the atomic density of the sample. The efficiency of the process is currently limited when on resonance due to the absorption of the 420 nm beam, and modifications should allow a significant increase in output power.