A method of compressing spectral bandwidth in spectral beam combining (SBC) of quantum cascade lasers (QCLs) by multiplexing a pair of blazed gratings arranged in a V-shaped configuration is proposed. The spectral interval can be compressed by increasing the number of diffractions via the round-trip propagation between gratings. Experimental results show that the SBC spectral interval of three diffractions is narrowed to 1/3 that of a single diffraction. The SBC power can be further improved within a given spectrum range by increasing the number of QCLs, which provides a feasible scheme to scale the SBC power and the brightness of QCLs.

We demonstrate a narrow-linewidth, high side-mode suppression ratio (SMSR) semiconductor laser based on the external optical feedback injection locking technology of a femtosecond-apodized (Fs-apodized) fiber Bragg grating (FBG). A single frequency output is achieved by coupling and integrating a wide-gain quantum dot (QD) gain chip with a Fs-apodized FBG in a 1-μm band. We propose this low-cost and high-integration scheme for the preparation of a series of single-frequency seed sources in this wavelength range by characterizing the performance of 1030 nm and 1080 nm lasers. The lasers have a maximum SMSR of 66.3 dB and maximum output power of 134.6 mW. Additionally, the lasers have minimum Lorentzian linewidths that are measured to be 260.5 kHz; however, a minimum integral linewidth less than 180.4 kHz is observed by testing and analyzing the power spectra of the frequency noise values of the lasers.

An extended spectral beam combining (SBC) configuration that folds the optical path of the combining laser into the non-SBC direction and doubly narrows the SBC spectrum by introducing a right angular prism is proposed. Similar combined power and beam quality but half of the spectral width and a smaller size are demonstrated by comparing the standard SBC with the proposed SBC of the same 800nm laser bar. It provides an effective way to miniaturize the SBC size, improve the SBC stability and compress the SBC spectrum simultaneously. As far as we know, this study is also the first to report on folding the SBC optical path to the non-SBC direction, which provides a new idea for the SBC source.

A novel, to the best of our knowledge, structure for spectral beam combining (SBC) is proposed, utilizing a polarization-separated feedback (PSF). A polarization separation element is introduced to separate the laser beam into a TE-polarized light and a TM-polarized light. The lower-power light is selected as the external feedback to adjust the resonant wavelength, while the other light is combined spectrally. Compared to the conventional SBC source with a similar feedback, the power and efficiency of the PSFSBC are improved by approximately 20%. Additionally, the beam quality in the non-SBC direction is optimized by 10%, and the power on the output coupler is reduced to nearly one-third. This provides an effective method for achieving an optimized SBC performance.

There is currently no transmission grating with good diffraction efficiency in the 4.7 μm band. Metal gratings at this wavelength are all reflective gratings which has a diffraction efficiency of lower than 90% and lower laser damage threshold. In this paper, we bring up a design of a multi-layer transmission grating with both high diffraction efficiency and wide working wavelength band. We have proved that the transmission grating made of composite materials has an average diffraction effectiveness of more than 96% throughout the whole spectral range of 200 nm. Meanwhile, the theoretically computed transmission grating has a highest first-order diffraction efficiency of more than 99.77% at 4746 nm. This multilayer dielectric film transmission grating’s optimized design may further boost spectral beam combining power, providing a practical technique for increasing SBC power and brightness.

A compact and highly efficient 670.8-nm semi-conductor master oscillator power amplifier (MOPA) system, with a unique optical design, is demonstrated. The MOPA system achieves a continuous-wave (CW) output power of 2.2 W, which is much higher than commercial products using semi-conductor devices. By comparing solid state lasers and dye lasers, higher wall-plug efficiency (WPE) of 20 % is achieved. Our developed laser system also achieves spectral line-width of 0.3 pm (200 MHz) and mode-hop free tuning range of 49 pm (32.6 GHz), which is very suitable for experiments of lithium atomic physics at several-watt power levels, such as Bose-Einstein condensation (BEC) and isotope absorption spectroscopy.