Electronic – Op-Amp Unity Gain Frequency

Am I doing something horribly wrong

The op-amp chosen is wholly unsuited to your expectations. The gain bandwidth product is 2 MHz and that means, as a unity gain amplifier, it will have a bandwidth of 2 MHz. With a gain of ten is will have a bandwidth of 200 kHz. Withy a gain of 100 its BW will be 20 kHz. You expect a gain of 300!

Also, the amplifier step response settling time is 150 us typically.

If not, can I get faster output response from this setup

To operate the way you plan, you need a much, much faster op-amp or you need to find a way of clamping the heater voltage to virtually zero volts so that the op-amp isn't having to recover from saturation and deal with a massive step response.

Is there a more appropriate approach to doing this (in hardware perspective)

I would consider using a sample and hold technique so that the thermocouple is disconnected from the input just prior to the heater powered on and reconnected just afterward the heater is powered off. Use a 100 pF capacitor for "holding" the thermocouple voltage when not connected.

With 1mA input across 470 ohms, that Vout of 0.47 volts will hardly challenge the slewrate; 0.47v is more in small signal region.

A high-capacitance sensor will kill your speed. And a slow-test-photon-pulse will confuse the measurements. What are your params?

And is the 50_ohm load the problem?

Consider, to debug the circuit, dropping in a common-base NPN transistor. If that is slow, then the sensor and the parasitic Vin node capacitance is the impairment.

^{simulate this circuit – Schematic created using CircuitLab}