Laser gain materials possessing high thermal conductivity and robust mechanical properties are key prerequisites for high power lasers. We show that diamond, when configured as a Raman laser, enables access to these and other extreme properties, providing an important new route to high power and high brightness beam generation. Recent achievements in pulsed and continuous wave oscillators, beam combining amplifiers, and single longitudinal mode oscillators are summarized, along with wavelength extension of these concepts through adaption to other pumps, use of Raman cascading, and intracavity harmonic generation. To date, diamond laser powers have attained 750 W with efficiency and beam quality so far unperturbed by nonlinear or thermally induced side-effects. Large factor brightness enhancement of low coherence inputs is demonstrated using multiple pump beams (via Raman beam combination) or highly multimode pumps for oscillator and amplifier configurations. Future directions for direct diode pumping, and for realizing extraordinary power and power density through reduced temperature operation and isotopically enriched diamond, are also discussed. Our results indicate that diamond is emerging as a generic high-power laser technology with advantages in terms of brightness (high average power and high beam quality) and wavelength range.

High average power lasers with high beam quality are critical for emerging applications in industry and research for defense, materials processing, and space applications. However, overcoming thermal effects in the gain medium remains the key challenge for increasing laser brightness at high powers. Here we report a means for increasing the beam brightness of high-power continuous-wave (CW) beams based on external cavity Raman lasers using diamond, a material with thermal properties far superior to any other laser material. With pump beam quality in the range M=2.3-7.3, efficient pump-limited conversion to an M=1.1 Stokes beam is achieved in all cases, with increases in brightness from the pump by factors as high as 12.7. The influence of pump beam quality on laser threshold and slope efficiency is analyzed. This Letter foreshadows an alternative approach for scaling the brightness of CW lasers using high-power, moderate beam quality pumps up to M=20 or more, such as thin-disk and slab lasers and fiber lasers operating in a mode instability regime.

Power conversion efficiency of a solar cell is a complex parameter which usually hides the molecular details of the charge generation process. For rationally tailoring the overall device efficiency of the dye-sensitized solar cell, detailed molecular understanding of photoinduced reactions at the dye-TiO 2 interface has to be achieved. Recently, near-IR absorbing diketopyrrolopyrrole-based (DPP) low bandgap polymeric dyes with enhanced photo-stabilities has been used for TiO 2 sensitization with moderate efficiencies. To improve the reported device performances, a critical analysis of the polymer-TiO 2 interaction and electron transfer dynamics is imperative. Employing a combination of time-resolved optical measurements complemented by low temperature EPR and steady-state Raman spectroscopy on polymer-TiO 2 conjugates, we provide direct evidence for photoinduced electron injection from the TDPP-BBT polymer singlet state into TiO 2 through the C=O group of the DPP-core. A detailed excited state description of the electron transfer process in films reveals instrument response function (IRF) limited (<110 fs) charge injection from a minor polymer fraction followed by a picosecond recombination. The major fraction of photo-excited polymers however, does not show injection indicating pronounced ground state heterogeneity induced due to non-specific polymer-TiO 2 interactions.Our work therefore underscores the importance of gathering molecular-level insight into the competitive pathways of ultrafast charge generation along with probing the chemical heterogeneity at the nanoscale within the polymer-TiO 2 films for optimizing photovoltaic device efficiencies.

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We report a quasi-continuous-wave external cavity Raman laser based on potassium yttrium tungstate (KYW). Laser output efficiency and spectrum are severely affected by the presence of high gain Raman modes of low frequency (< 250 cm^-1) that are characteristic of this crystal class. Output spectra contained frequency combs spaced by the low frequency modes but with the overall pump-to-Stokes conversion efficiency at least an order of magnitude lower than that typically obtained in other crystal Raman lasers. We elucidate the primary factors affecting laser performance by measuring the Raman gain coefficients of the low energy modes and numerically modeling the cascading dynamics. For a pump polarization aligned to the N_g crystallo-optic axis, the 87 cm^-1 Raman mode has a gain coefficient of 9.2 cm/GW at 1064 nm and a dephasing time T₂ = 9.6 ps, which are both notably higher than for the 765 cm^-1 mode usually considered to be the prominent Raman mode of KYW. The implications for continuous-wave Raman laser design and the possible advantages for applications are discussed.