
\section{Miniature hyperpolarizer construction}
In this section we provide more information about the construction of the hyperpolarizer devices. \zfr{photo-view} shows isometric and side views of device placed on a tabletop. As pointed out in the main paper, all the electronic microwave and optical components are attached to a single aluminum plate (6061 alloy, 0.25")  in the center of the device. The outer frame (8020) acts as scaffolding and provides rigid support to the plate.

To simplify the power handling and delivery, the device consists of a single umbilical cord, interfaced to a rigid 16-pin connector (TME DA-016), that carries power to the various components (Helmholtz coil, amplifiers, VCOs and ramp generators). Step down buck-convertors (DROK) shown on the front panel in \zfr{photo-view} allow the use of a single 28V 10A source to deliver the requisite power to the various devices, obviating the need for separate power supplies for each component. The device side views in panels \zfr{photo-view}B also indicate the relatively simple wiring involved, the power to the devices being carried by means of inexpensive Molex connectors and ribbon cables. The microwave components are interconnected by means of flexible SMA cables (Fairview), while the microwave loop antenna is obtained by stripping and self shorting a semirigid coaxial (MiniCircuits CBL).





\begin{figure}[t]
		 \centering
  {\includegraphics[width=0.42\textwidth]{circuit_diagram2.png}}
  \caption{\T{Homemade quadruple voltage ramp generator} that when interfaced with the VCO sources generate frequency sweeps that drive ${}^{13}\R{C}$ nuclear hyperpolarization at low fields. We employ MDACs (LTC1590) to generate sawtooth voltage ramps, the ramp gain and offset values being set by a DAC (MCP4822). All chips are interfaced via a PIC microcontroller running a 50kHz clock. By using a total of two MDAC and DAC chips, we create the quadruple voltage ramp generator that can cascade sweeps from four VCOs to produce the swept MW frequency comb. The entire circuit can be constructed in a miniature footprint.}
\zfl{circuit}	
\end{figure}

\section{Electronics for frequency sweep generation}
At the heart of the DNP process is the use of microwave irradiation that sweeps the NV center ESR spectrum to transfer polarization to the ${}^{13}\R{C}$ nuclei. We employ miniature voltage controlled oscillator (VCO) microwave sources for this task. Frequency sweeps are generated by applying sawtooth voltage ramps at the VCO tuning ports. The mean voltage of the ramps are set by the center of the desired sweep band, while the ramp amplitude (gain) is set by sweep bandwidth.
Given the typical frequency-voltage (f-V) characteristics of the sources (Minicircuits ZX95-3800A+), this corresponds to a voltage ramp of 0-20V with the center 10V.

We generate the voltage ramps by means of a home built circuit board employing a PIC microprocessor (PIC30F2020, running at 50kHz), and a multiplying digital to analog convertors (MDAC). The LTC1590 MDACs have 12-bit resolution, and indeed the sawtooth ramps are simple to setup digitally since one just needs to cycle through the binary voltage input values at the desired sweep rates. The ramp gains are configured by a set of independent serial DACs (MCP4822), that are also controlled by the PIC. Since the MDACs produce AC sawtooth ramps, they have to be DC offset to the center of the sweep band. This is achieved by using another DAC, and finally summing them via an operational amplifier (LM124) noninverting adder and gain stage. Note that both the MDACs, DACs and opamps we employ are all dual chip packages and thus allow the use of fewer overall components.

Importantly this also enables the simple cascading of multiple VCO sources to gain in DNP enhancements. Effectively, the $N$ microwave sources can be combined to generate swept MW frequency combs, that can sweep different parts of the ESR spectrum simultaneously and obtain multiplicative DNP gains that scale linearly with $N$. The use of two MDACs, DACs, and four opamps allow one to cascade four VCO sources, which we have found to be optimal given the relatively narrow frequency bandwidths at low fields.



\begin{figure}[t]
  \centering
  {\includegraphics[width=0.5\textwidth]{sample_height.pdf}}
  \caption{\T{Experimental characterization of MW and field inhomogeneity.} (A) \I{MW inhomogeneity.} Using a thin single crystal sample (3\% ${}^{13}\R{C}$ enriched) with thickness $\approx$250$\mu$m we map the effect of MW inhomogeneity in our DNP experiments via the obtained ${}^{13}\R{C}$ hyperpolarization enhancement. We use a 4mm MW loop antenna in these experiments, and the results indicate that a volume of over 10mm$^3$ can be hyperpolarized in under 60s of pumping \I{Inset:} schematic of experiment where sample height above the loop antenna is varied in 100$\mu$m increments. (B) \I{Field inhomogeneity.} We measure (via a Hall probe) the polarizing magnetic field produced by the Helmholtz coils as a function of sample height for 1A and 2A applied current. Panels indicates that ${}^{13}\R{C}$ hyperpolarization can function even under highly inhomogeneous MW settings and field environments. }
 \zfl{height}	
\end{figure}

\section{Device performance under field and MW inhomogeneity}
We now detail experiments that characterize the performance of the hyperpolarizer in the presence of microwave irradiation for polarizing field inhomogeneities. In \zfr{height}A, we employ a 3\% enriched ${}^{13}\R{C}$ single-crystal sample of thickness $\approx$250$\mu$m mounted flat in an 8mm NMR tube (see inset), and a 4mm microwave loop antenna interfaced to the 16W MW amplifier for DNP excitation. The sample is positioned \I{above} the antenna and subsequently moved in incremental 100$\mu$m steps and the hyperpolarization enhancements are recorded at each sample height. Experiments are performed in the $\textbf{B}_{\R{pol}}=$20mT fringe field of a 7T magnet, which has a very slowly varying field gradient and hence the obtained enhancements report the device performance under varying microwave powers. As is evident (\zfr{height}A) far away from the antenna the loss in enhancement is approximately linear with distance, which is on account of the microwave power being too low to efficiently excite DNP. On the other hand we notice a relatively homogeneous region approximately constrained by the radius of the loop, where the enhancements remain fairly constant, indicating the ability to efficiently excite DNP in a $\sim$16mm$^3$ hemispherical volume. Considering the density of diamond ($ \rho = 3.51$mg/mm$^3$), this corresponds to a total mass of 50mg, and a hyperpolarization throughput of $\sim$50mg/min since DNP buildup saturates in about a minute (Fig. 1B of main paper).

In \zfr{height}B we study the homogenity of the polarizing field $\textbf{B}_{\R{pol}}$ produced by the Helmholtz coil (shown for two current values, 1A and 2A, corresponding respectively to coil field values of 70.2G and 142.7G) here defined as the percent difference of the magnetic field from the central field intensity. Measurements are obtained by mounting a sensitive Hall probe (Lakeshore HMMA-2504-VR-10) on a mechanical stage and measuring the polarizing field as a function of height. Given that the heights of the packed diamond powder typically used in device operation (2-3mm placed in the center of the Helmholtz pair), limited in part by optical penetration depth, this corresponds to a magnetic field homogenity of $<$10\% for a separation distance of 3mm at an operating current of 2A. Note that DNP on powders is relatively immune to inhomogeneity in the polarizing field, since the NV centers electronic spectrum is already orientationally broadened by several hundred MHz. Inhomogeneity only adds a slight additional broadening, and does not significantly affect the obtained DNP enhancements.


\begin{figure}[t]
  \centering
  {\includegraphics[width=0.4\textwidth]{hall.png}}
  \caption{\T{Experimental characterization of Hall probes for field estimation.} (A) Red (blue) lines indicate the measured (estimated) fields from the Hall probes (indirectly from ESR measurements of the NV power pattern). Field is produced by the Helmholtz coils in the 20mT fringing field of a 7T NMR magnet. (B) Panel highlights the embedded tri-orthogonal Hall probes allowing one to measure the magnetic field in the vicinity of the sample being hyperpolarized. (C) Using 100MHz sweep windows we map out experimentally the NV ESR spectrum (points). Blue line indicates best fit to the simulated ESR spectrum, while the red line is the predicted spectrum using the measured values from the Hall probes alone. We therefore slightly overestimate the field using the Hall probes, by a relatively small amount $\approx$2.04mT, which we ascribe to being because the $\bz$-axis Hall probe is $\approx$1mm above the microwave loop antenna.}
 \zfl{hall}	
\end{figure}




\section{Hall probes for field estimation}
We now provide more details of the embedded Hall sensors (AsahiKASEI EQ-731L, magnetic sensitivity$\sim$65mV/mT) that allow the in-situ measurement of magnetic field used for hyperpolarization experiments (Fig. 3A of main paper). The probes enable high flexibility in the operation and installation of the device in the fringe fields of NMR detection magnets, since an evaluation of the $B_{\R{pol}}$ field allows one to precisely estimate the frequency range to sweep over for optimal DNP enhancements (Fig. 3 of main paper), as well as allowing to supplement the fringe field with an applied current in the Helmholtz coils.

The Hall probes are mounted in a tri-orthogonal configuration in the vicinity of the microwave loop antenna (see \zfr{hall}B for a zoomed view). This allows the measurement of the vector magnetic field $\textbf{B}_{\R{pol}}$ seen by the NV electrons during DNP. In order to characterize the accuracy of the measured field value, \zfr{hall}C shows the comparison between the directly measured field, and the field estimated by fits of the indirectly obtained NV center powder patterns via hyperpolarized ${}^{13}\R{C}$ NMR by performing DNP experiments on 100MHz windows that are swept across in frequency space (see Fig. 2B of main paper). We obtain a close and consistent agreement between the two methods (see \zfr{hall}C), the Hall measurement being offset from the exact field felt by NV centers by $\approx$2mT. We ascribe this slight overestimation to be because the Hall sensor in the $\bz$ direction is about 1mm away from the loop antenna (see \zfr{hall}C). In summary the use of these miniature low-cost Hall sensor chips enable the versatile operation of the hyperpolarizer device in a variety of field environments.

 \begin{figure}[t]
 		 \centering
   {\includegraphics[width=0.33\textwidth]{solvent_fig.pdf}}
   \caption{\T{DNP of particles in solution.} 200$\mu$m natural abundance particles immersed in solvents and biologically relevant liquids.  Variations arise from differences in optical penetration. Shaded regions are guides for the eye.   Since the DNP occurs at room temperature and with modest laser and MW powers, large hyperpolarization enhancements can be gained even when the particles are placed in optically nontransparent liquids such as blood. }
   \zfl{solvents}	
 \end{figure}
 
 \begin{figure*}[t]
  \centering
  {\includegraphics[width=0.98\textwidth]{fmoc_full.pdf}}
   \caption{\T{Background suppression experiments.} Full data set of experiments depicted in Fig. 6C of the main paper. Here the red solid (blue dashed) lines indicate the ${}^{13}\R{C}$ NMR spectrum obtained with low to high (high to low) frequency sweeps. Black lines and shaded regions are extracted the ${}^{13}\R{C}$ diamond spectra obtained by subtracting the results. The panels show increasing concentrations of Fmoc-Gly-OH-${}^{13}\R{C}_2$ background signal, normalized here for 50 diamond particles (see Methods). In the last panel, also depicted in Fig. 6D of the main paper, the peak suppression of the background signal exceeds two orders of magnitude.}
 \zfl{fmoc-full}	
\end{figure*}


\section{DNP of particles in solution}
Our hyperpolarizer is fully operational at room temperature and employs very modest amount of laser and MW powers. This allows the DNP process in diamond performed at ambient conditions with the particles dry as well as in solution. In \zfr{solvents} we study this in detail for particles immersed in a wide range of solutions, including common solvents and biological fluids. We find that high enhancements can be preserved. It is noteworthy that hyperpolarization was possible rather efficiently even for particles that were immersed in blood which is viscous and less optically clear (\zfr{solvents}). Overall this illustrates the advantages of room temperature DNP at low magnetic fields and employing low optical and microwave powers.

This also enables the experiments in Fig. 6C of the main paper where we perform DNP of particles in a solution of ${}^{13}\R{C}$ enriched the liquid, having a chemical shift very close to the diamond peak, and showed how by successive experiments with alternate hyperpolarization signs one could suppress very effectively this ${}^{13}\R{C}$ background. For completeness in \zfr{fmoc-full}, we present the complete data set that was used in Fig. 6E of the main paper. In the last panel, (also shown in Fig. 6D), we obtain a ${}^{13}\R{C}$ background suppression exceeding two orders of magnitude.

\section{Measurement of field dependent ${}^{13}\R{C}$ lifetimes}
We outline herein the measurement strategy and error estimation in experiments presented in Fig. 4 of the main paper studying the field dependence of $^{13}$C nuclear lifetimes by interfacing the portable hyperpolarizer with a home built field cycling instrument (see Methods). The instrument consists of a high precision (50$\mu$m) conveyor belt actuator stage in the fringe field of a 7T magnet, allowing a fine step field sweep over a large range from $\sim$10mT-7T. We are able to translate the sample between different fields precisely with sub-second switching speeds (measured to be $648\pm4$ms for full 20mT-7T travel), and with little loss in enhancement. We measure a striking field dependence (see Fig. 4), the nuclear lifetimes falling rapidly below a field of $\approx$57mT and reaching remarkably high values $>$6min beyond 100mT.

In order to hasten measurement times, and to obtain a map of nuclear $T_1$ at a large number (55) of field points, we use an accelerated measurement strategy detailed below. We first measure the full $T_1$ relaxation decays for a subset of points, $\sim$20 in number, uniformly sampled from low to high field. To a very good approximation we find that the relaxation decays are mono-exponential (see inset of Fig. 4C of main paper). Next we measure for all 55 field values an accelerated 1D relaxation measurement where we measure the signal decay after a fixed waiting time (60s) after hyperpolarization and subsequent rapid transfer to the field of interest. Due to the reduced dimensionality of this measurement, it is possible to rapidly measure a large number of field points. We now map the obtained field-dependent enhancement decay values from this 1D data set to nuclear $T_1$ values assuming mono-exponential decays. 

This is done by first calculating the enhancement at zero time $\epsilon(t=0)$ at fields with both enhancement decay and 1D measurements. Using the $T_1\pm \sigma_{T_1}$ estimates from our fit, we solve for this initial enhancement $\epsilon(0) = \epsilon(60)e^{\frac{60}{T_1}}$ assuming mono-exponential decay, with corresponding error
$\sigma_{\epsilon(0)} = \frac{60 \cdot \epsilon(60)\cdot \sigma_{T_1} e^{60/T_1} }{T_1^2}$.
We average our calculations of $\epsilon(0)$ over measurements at high field ($>$500mT), as fast relaxation times at low fields make it challenging to obtain accurate estimations of $\epsilon(0)$. During calculation of the mean, we assigned weights $w = \sigma_{\epsilon(0)}^{-2}$ for each measurement. Thus for N values of $\epsilon(0)$, our resulting mean $\overline{\epsilon}(0)$ has error $\sigma_{\overline{\epsilon}(0)} = \left(\sqrt{\sum_i^N w_i}\right)^{-1}$. We then map our 60s enhancement measurements $\epsilon(60)$ to $T_1 = 60/\log\left(\frac{\overline{\epsilon}(0)}{\epsilon(60)}\right)$, with associated error $\sigma_{T_1} = \frac{60 \cdot \sigma_{\overline{\epsilon}(0)}}{\overline{\epsilon}(0)}/\left[\log \left(\frac{\overline{\epsilon}(0)}{\epsilon(60)}\right)\right]^2$. This is the data plotted in Fig. 4 of the main paper.

In order to fit the obtained relaxation profiles, we fit a Lorentzian decay to the relaxation rate at low fields and assume a constant offset to the rates at high field. Its functional form with respect to field $B$ is $R_1(B)=\fr{1}{T_1(B)}=\frac{2A}{\pi} \frac{W}{4 B^2 + W^2} + c$, with fitting parameters $A, W, c$ describing the amplitude, width and vertical offset of the Lorentzian respectively. 

We have found a qualitatively similar field profile for all 1\% $^{13}$C (natural abundance) including for single crystals and powders (5-200$\mu$m) both CVD as well as HPHT manufactured. A more detailed study of the factors that cause this dramatic field dependence, and accompanying ESR measurements of these diamond samples, will be presented in a forthcoming publication.







\begin{figure}
  \centering
  {\includegraphics[width=0.4\textwidth]{Mechanism_Revised.pdf}}
  \caption{
\textbf{Mechanism of polarization transfer.} (A) Energy levels of an NV electron spin hyperfine-coupled to a ${}^{13}\R{C}$ nuclear spin. Quantum numbers in all kets refer to electron and nuclear spins, in that order; the notation for the nuclear spin states highlights the manifold-dependent quantization axis, in general different from the magnetic field direction. (B) Calculated energy diagram in the rotating frame corresponding to the $m_S=0\leftrightarrow m_S=-1$ subset of transitions (dashed rectangle in (A)) assuming a hyperfine coupling $A_{zz}=+0.5$ MHz. (C) Same as in (B) but for $A_{zz}=-0.5$ MHz. In (B) and (C) we assume $B$=10 mT, $\theta$=45 deg., and use a transverse hyperfine constant $A_{zx}=0.3|A_{zz}|$. Colored solid circles denote populations at different stages during a sweep in the direction of the arrow, and faint dashed circles indicate the narrower avoided crossings where population transfer takes place. }
\zfl{mechanism}
\end{figure}


\section{Hyperpolarization Mechanism}
We now briefly describe the low field DNP mechanism that governs the polarization transfer in our experiments. For more details, and experimental characterization of the mechanism, we point the reader to Ref. \cite{Ajoy17, Zangara18}. Consider for simplicity a NV center coupled to a single ${}^{13}\R{C}$ nuclear spin. The Hamiltonian of the system is,
\begin{equation}\label{eq:1}
\begin{aligned}
	\mH = {} & \Delta S_{z}^2 - \gamma_e \vec{B} \cdot \vec{S} - \gamma_n \vec{B} \cdot \vec{I} + A_{zz}S_{z}I_{z}\\
	& + A_{yy}S_{y}I_{y} + A_{xx}S_{x}I_{x} + A_{xz}S_{x}I_{z} + A_{zx}S_{z}I_{x}
\end{aligned}
\end{equation}
where $\vec{S}$ and $\vec{I}$ respectively denote the NV and ${}^{13}\R{C}$ vector spin operators, and $\vec{B}$ is the magnetic field (10-30 mT) at angle $\theta$ ($\phi$) to the NV axis. Within the $m_s=\pm1$ states, the hyperfine coupling produces a ${}^{13}\R{C}$ splitting,
\begin{equation}\label{eq:2}
	\omega_{C}^{(\pm1)} = \sqrt{(A_{zz}\mp\gamma_{n}B\cos\theta)^2 + A_{zx}^2}
\end{equation}
For the $m_s=0$ manifold, second-order perturbation theory leads to the approximate formula~\cite{Alvarez15},
\begin{equation}\label{eq:3}
\begin{aligned}
	\wt{\omega}_L \approx {} & \gamma_{n}B \\
	& + 2\Big(\frac{\gamma_{e}B}{\Delta}\Big) \sin\theta \big(\sqrt{A_{xx}^2 + A_{zx}^2} \cos^2\phi  + A_{yy}\sin^2\phi \big)
\end{aligned}
\end{equation} 
From Eqs. \ref{eq:2} and \ref{eq:3} we conclude that each manifold (including the $m_s=0$ manifold) has its own, distinct quantization axis which might be different from the direction of the applied magnetic field. In particular, the second term in Eq. \ref{eq:3} can be dominant for hyperfine couplings as low as 1 MHz (corresponding to nuclei beyond the first two shells around the NV) if $\theta$ is sufficiently large, implying that, in general, ${}^{13}\R{C}$ spins coupled to NVs misaligned with the external magnetic field experience a large frequency mismatch with bulk carbons, even if optical excitation makes $m_s=0$ the preferred NV spin state.

Assuming fields in the range 10-30 mT, it follows that ${}^{13}\R{C}$ spins moderately coupled to the NV (300 kHz $\lesssim |A_{zz}|\lesssim$ 1 MHz) are dominant in the hyperpolarization process because they more easily spin diffuse into the bulk and contribute most strongly to the observed NMR signal at 7T. For sweep rates near the optimum ($\sim$ 40 MHz/ms), the time necessary to traverse the set of transitions connecting $m_s=0$ with either the $m_s=-1$ or $m_s=+1$ manifolds is relatively short \big($\lesssim$ 30 $\mu$s for weakly coupled carbons\big) meaning that optical repolarization of the NV preferentially takes place during the longer intervals separating two consecutive sweeps, as modeled in \zfr{mechanism}. 

Nuclear spin polarization can be understood as arising from the Landau-Zener crossings in \zfr{mechanism}. Efficient polarization transfer takes place when the narrower LZ crossings connect branches with different electron and nuclear spin quantum numbers, precisely the case in the $m_s=0\leftrightarrow m_s=-1$ ($m_s=0\leftrightarrow m_s=+1$) subset of transitions when the hyperfine coupling is positive (negative). When probing ensembles, both sets of transitions behave in the same way, i.e., ${}^{13}\R{C}$ spins polarize positive in one direction, negative in the other. A more detailed exposition of the hyperpolarization mechanism and simulations are presented in Ref. \cite{Ajoy17}.


\end{document}
